Talks (Invited and contributed)

X-rays of stellar Coronae with Chandra and XMM-Newton: flares and elemental composition in Stellar Atmospheres

Marc Audard (Columbia Astrophysics Laboratory)
Observations of magnetically active stars with Chandra and XMM-Newton have deepened our knowledge of the physics of the atmospheres in late-type stars. In this review talk, I will discuss two topics that have profited significantly from Chandra and XMM-Newton. Of particular interest, studies of the elemental composition of stellar coronae have taken advantage of the high spectral resolution available with the grating instruments onboard these satellites. I will summarize the status of our knowledge and discuss the elemental composition in a variety of stellar coronae. Secondly, I will focus on the topic of flares in stellar coronae, and will review the contributions made by XMM-Newton and Chandra to X-ray and multi-wavelength studies.

The decrease in differential rotation with decreasing stellar mass in a sample of young rapidly rotating main sequence stars

John Barnes (University of St. Andrews)
Andrews Collier Cameron (University of St. Andrews)

By making use of Doppler imaging techniques we present new differential rotation measurements for stars in the K3V--M2V spectral range.
We show that an homogeneous sample of young rapidly rotating G2V to M2V stars exhibit a trend towards decreasing latitude dependent rotation with decreasing mass. The implied increase in the degree of solid body rotation with increasing relative convection zone depth is particularly pertinent to fluid circulation and stellar dynamo models.
http://star-www.st-and.ac.uk

Stellar butterfly diagrams

Svetlana V. Berdyugina (Institute of Astronomy, ETH Zürich)
Cyclic latitude migration of sunspot zones results in the famous butterfly diagram which reflects the dynamo process in the Sun. In the presence of differential rotation the latitude variations induce longitude migration of non-axisymmetric fields. Therefore, migration of long-lived spot activity regions (active longitudes) combined with the information on the differential rotation can be used to deduce butterfly diagrams. Here I present a new technique which is able to recover stellar butterfly diagrams from the analysis of long-term photometric data and Doppler images. I discuss the results for different types of stars and compare them with the solar counterpart.
http://www.astro.phys.ethz.ch/staff/berdyugina/berdyugina_nf.html

Spectroscopy of cool stars in the Local Group

Piercarlo Bonifacio (Istituto Nazionale di Astrofisica - Osservatorio Astronomico di Trieste)
The advent of 8m class telescopes, equipped with high resolution spectrographs has opened up the possibility to study the cool giant stars in the Local Group galaxies with the same detail and accuracy which previously was possible only for Galactic stars. These spectra allow to measure accurate radial velocities and chemical abundances for a large number of elements. The radial velocities provide crucial information on the mass and internal dynamics of these galaxies. The chemical abundances allow to break the age-metallicity degeneracy, which hampers the interpretation of the colour-magnitude diagrams, and to constrain the chemical evolution of the galaxies. In this talk I shall review the results of recent spectroscopic investigations of dwarf galaxies, satellites of the Milky Way. A very interesting picture is emerging which shows that several of these galaxies have suffered a complex star formation history and follow chemical evolutionary paths which are clearly distinct from that followed by the Milky Way. At least in one case, Sagittarius, there is clear evidence that the interaction with the Milky Way has played an important role in the evolution of the galaxy.

X-ray emission mechanisms in protostellar jets

Rosaria Bonito (Università di Palermo, Pizza del Parlamento 1, 90134 Palermo, Italy)
Salvatore Orlando (INAF -- Osservatorio Astronomico di Palermo)
Giovanni Peres (Università di Palermo)

Prompted by the recent detection of X-ray emission from Herbig-Haro objects, we studied the interaction between a supersonic jet originating from a young stellar object and the ambient medium with the aim to investigate the mechanisms of X-ray emission. Our model takes into account the radiative losses from optically thin plasmas and the Spitzer's thermal conduction including saturation effects. We explored the parameter space defined by the density contrast between the ambient density and the jet and by the Mach number to infer the configurations which can give rise to X-ray emission. From the models, we derived X-ray emission as predicted to be observed with Chandra/ACIS-I and XMM-Newton/EPIC-pn, using the MEKAL spectral code and including the absorption of interstellar medium. Here we discuss a representative case which produces, without any ad-hoc assumption, X-ray emission with characteristics very similar to those observed in the protostellar jet HH 154. We find that the X-ray emission originates from a blob localized just behind the bow shock, moving with velocity 500 km/s. We predict, therefore, a detectable proper motion of the X-ray blob, interesting for future observations.

First determination of the orbit of a binary L-dwarf

Hervé Bouy (Max-Planck-Institut für extraterrestrische Physik)
Wolfgang Brandner, Eduardo L. Martín, Jerôme Bouvier, Gaspard Duchene, Rainer Koehler
With spectral properties intermediate between those of giant planets and late-type stars, ultra-cool and brown dwarfs have opened a new chapter in the study of atmospheric physics and chemistry. One of the ultimate goals of a theory of very low mass and sub-stellar objects is an accurate determination of the mass of an object based on spectroscopic characteristics and luminosity. The degeneracy in the mass-luminosity (age-temperature) relation for ultra-cool dwarfs makes it difficult to pin down their physical properties. Luminosities and effective temperatures of ultra-cool dwarfs are a function of both age and mass so that an older, slightly more massive ultra-cool dwarf can exhibit the same effective temperature as a younger, less massive one. Therefore, dynamical masses, which are model-independent, are highly required in order to calibrate the mass-luminosity relation.
We will present the results of astrometric, photometric and spectroscopic observations leading to the determination of the orbit and dynamical masses of the binary L dwarf 2MASSW J0746425+2000321. High angular resolution observations spread over almost 4 years and obtained with the Hubble Space Telescope, the ESO Very Large Telescope, and at the W. M. Keck Observatory allow us to cover ≈ 60 % of the orbit, and, for the first time, to derive a precise estimate of the total and individual masses of such a late-type object.
http://www.mpe.mpg.de/~hbouy/

The new cool subdwarfs: metal-poor stars and brown dwarfs extending into the L and T dwarf regimes

Adam Burgasser (UCLA, Dept. Physics & Astronomy)
J. Davy Kirkpatrick (Caltech/IPAC)
Sebastien Lepine (American Museum of Natural History)

M-type subdwarfs (sdMs) are the most common component of the metal-poor stellar halo, probing early stellar masses down to ≈ 0.1 M_ˆ. Most of the coolest sdMs have been previously identified in photographic plate proper motion surveys, notably Luyten's LHS and NLTT surveys amongst others. New red optical and near-infrared (NIR) proper motion and photometric surveys are now turning up the next generation of cool subdwarfs that straddle the stellar/substellar boundary, including metal-poor analogs of the L and T spectral classes. In this presentation, I will review some of these discoveries, including many of the coolest brown dwarfs currently known (Teff 900 K). I will show how metallicity strongly affects the emergent spectral energy distributions and atmospheric properties (e.g., cloud formation) of very cool subdwarfs, as well as their thermal evolution. Finally, I will examine the prospects for a NIR proper motion survey, including some early results, and show how measurement of the metal-poor LF below 2000 K could provide strong constraints on the star formation history of this population as a whole.
http://www.astro.ucla.edu/~adam

Seismology of the Sun and solar-like stars

Jørgen Christensen-Dalsgaard (Dept. of Physics and Astronomy University of Aarhus, Denmark)
Helioseismology has provided very detailed information about the properties of the solar interior. The inferences of the internal structure have given an important test of stellar- evolution theory, as well as of the physical properties of matter under stellar conditions. Equally significantly the observations have given us the first detailed view of the internal rotation of a star, of great importance to the understanding of the evolution of stellar rotation and likely involved in the generation of the cyclic solar magnetic activity.
In recent years observational advances have allowed the detection and study of solar-like oscillations in other stars. Although the data will never be as detailed as for the Sun, these results are crucial in extending the observational basis for stellar-evolution studies to a broad range of stars. Continuing ground-based observations and on-going and planned satellite missions will greatly enhance these studies over the coming years.
http://astro.phys.au.dk/~jcd

New insights into Solar Wind Physics from SOHO

Steven Cranmer (Harvard-Smithsonian Center for Astrophysics)
The Solar and Heliospheric Observatory (SOHO) was launched in December 1995 with instruments designed to answer long-standing questions about the Sun's internal structure, atmosphere, and solar wind. This presentation reviews the new understanding of the physical processes responsible for the solar wind that have come from the past 8 years of SOHO observations, analysis, and theoretical work. For example, the UVCS instrument on SOHO has revealed the acceleration region of the high-speed solar wind to be far from simple thermal equilibrium. Evidence for preferential acceleration of ions, 100 million K ion temperatures, and departures from Maxwellian distributions all point to specific collisionless heating processes. The slow solar wind, typically associated with bright streamers, has been found to share some of the nonthermal characteristics of the fast wind. Abundance measurements from spectroscopy and visible coronographic movies from LASCO have led to a better census of the plasma components in the slow wind. This talk will also review the origins of the solar wind in the lower atmosphere as elucidated by SUMER and CDS, as well as the impact of SOHO on space weather prediction.
http://cfa-www.harvard.edu/~scranmer/

A wind analysis of an evolved giant -- phase-resolved FUSE and HST/STIS observations of an eclipsing symbiotic binary

Cian Crowley (Trinity College, Dublin)
Brian Espey (Trinity College, Dublin)
Steve McCandliss (Johns Hopkins University, Baltimore, MD)

A major outstanding problem in stellar astrophysics lies in understanding the wind generation mechanism by which evolved giants lose mass. Phase-resolved observations of eclipsing symbiotic binary systems, containing a mass-losing giant and a hot white dwarf, are ideal for studying the wind generation mechanisms in evolved stars. For such systems it is possible to use the orbital motion of the dwarf through the giant's wind to provide a pencil-beam view through the circumstellar gas. FUV observations can probe different layers of the wind in absorption, permitting the derivation of the velocity profile and providing valuable, spatially-resolved diagnostics of the cool wind.
We present a series of new FUSE and HST/STIS observations of two such systems and discuss our findings. The velocity profiles, and by implication, wind generation mechanisms for these giants are found to differ from those predicted by commonly used parametrisations. The phasing of our observations allow us to examine the density, temperature and velocity structure in the wind acceleration region, as well as the composition of the outflowing material.

The luminosity function of ultracool dwarfs

Kelle Cruz (University of Pennsylvania and American Museum of Natural History)
We have created a statistically complete sample of M7--L8 dwarfs within 20 pc using the 2MASS Second Data Release. With this dataset, we present the first robust measurement of the luminosity function of objects that span the stellar/brown dwarf boundary. In addition, we have doubled the number of ultracool dwarfs known within 20 pc. I will describe these results, summarize its implications on the mass function, and discuss the prospects for the future.

Cool stars, the Sun and Climate Variability: Is there a connection ?

Ulrich Cubasch (Meteorologisches Institut, Freie Universität Berlin, Germany)
E. Zorita (KSS Forschungszentrum, Geesthacht, Germany)
F. Kaspar / F. Gonzales-Rouco (Max-Planck-Institut für Meteorologie, Hamburg, Germany / Universidad Complutense, Madrid, Spain)

The sun influences the climate in two ways: a) by varying its radiative output and b) by changes of the orbital parameters of the earth around the sun. The first effect is considered to be at least partially responsible for the recently observed global warming. This effect has been studied in a number of model experiments simulating the recent millennium. The model simulates the medieval warm period and the Late Maunder Minimum with temperature changes comparable to the ones observed at present. However, the warming observed recently cannot solely be attributed to changes in solar forcing.
The orbital parameters take effect in more geological timescales. Here the interest focuses on the recent ice ages and warm periods as well as the transitions between ice ages and warm periods. A simulation for 125 ky bp (kilo years before present), which was the last warm period (Eem) as well as for 115 ky bp, i. e. the transition between warm period and ice age will be presented. The simulation of the Eemian compares well with pollen derived proxy data, and the simulation of the 115 ky bp climate shows the built up of an ice sheet in the northern part of North America.

Spitzer spectroscopy of low-mass stars and brown dwarfs

Michael Cushing (SETI Institute/NASA Ames Research Center)
Tom Roellig (NASA Ames Research Center)

With the recent launch of the Spitzer Space Telescope, a heretofore untapped wavelength range (5--40 µm) in the study of low-mass stars and brown dwarfs has been opened. To take advantage of this unique opportunity, the science team of the Infrared Spectrograph has initiated a spectroscopic survey of a sample of M, L, and T dwarfs under the Guaranteed Time Observing program. We will present the initial results from this survey including the first detection of the 7.8 µm CH₄ band and 10.5 µm NH₃ band in the spectra of brown dwarfs.

Generation of large-scale magnetic fields and flows in fully convective stars

Wolfgang Dobler (Kiepenheuer-Institut für Sonnenphysik/University of Calgary)
Axel Brandenburg (NORDITA, Copenhagen)
Michael Stix (Kiepenheuer-Institut, Freiburg)

We present results of numerical simulations of convection and magnetic field evolution in fully convective stars like M-dwarfs. The model consists of a rotating gas sphere in a spherically symmetric gravity potential, with heating near the centre and cooling at the surface.
While magnetic fields can grow even in the absence of rotation, the growth is faster if rotation is present. For inverse Rossby numbers considerably larger than unity, the magnetic spectrum peaks at moderate wave number during the kinematic dynamo phase, but after saturation, the magnetic field is dominated by large scales.
We also discuss the pattern of differential rotation and meridional circulation that is generated by convection and influenced by the magnetic field.

Wavelength shifts in solar-type spectra

Dainis Dravins (Lund Observatory, Sweden)
Lennart Lindegren, Hans-Günter Ludwig, Søren Madsen (Lund Observatory, Sweden)

Spectral-line displacements away from the wavelengths naively expected from the Doppler shift caused by stellar radial motion may originate as convective shifts (correlated velocity and brightness patterns in the photosphere), or as gravitational redshifts. Absolute lineshifts, in the past studied only for the Sun, are now accessible for other stars thanks to astrometric determination of stellar radial motion, and spectrometers with accurate wavelength calibration.
Comparisons between spectroscopic apparent radial velocities and astrometrically determined radial motions reveal greater spectral blueshifts in F-type stars than in the Sun (as theoretically expected from more vigorous convection), further increasing in A-type stars (possibly due to atmospheric shockwaves).
Work is in progress to survey the spectra of the Sun and several solar-type stars for "unblended" photospheric lines of most atomic species with accurate laboratory wavelengths. One aim is to understand in what detail it will be feasible to verify hydrodynamic stellar models. These may predict bisectors and shifts for different classes of lines, but there will not result any comparison with observations if such lines do not exist in real spectra, or are too blended for meaningful measurement.
http://www.astro.lu.se/~dainis/

Mid-infrared interferometry of the Mira variable RR Sco with the VLTI MIDI instrument

Thomas Driebe (Max-Planck Institute for Radio Astronomy)
Keiichi Ohnaka (Max-Planck Institute for Radio Astronomy)
Gerd Weigelt (Max-Planck Institute for Radio Astronomy)

We present the results of the first interferometric observations of the Mira variable RR Sco with the MID-infrared Interferometer (MIDI) coupled to the European Southern Observatory's Very Large Telescope Interferometer (VLTI), together with K-band observations using VLTI VINCI. The observations were carried out in June 2003, using unit telescopes UT1 and UT3, as part of the Science Demonstration Time program. Projected baseline lengths ranged from 73 to 102m, and a spectral resolution of 30 was employed in the observations.The uniform-disk diameter was found to be 18 mas between 8 and 10 micron, while it gradually increases longward of 10 micron to reach 24 mas at 13 micron. The uniform-disk diameter between 8 and 13 micron is significantly larger than the K-band uniform-disk diameter of 10.2 ± 0.5 mas measured with VLTI VINCI three weeks after the MIDI observations with projected baseline lengths of ≈ 15--16 m. Our model calculations show that optically thick emission from a warm molecular envelope consisting of water and SiO can cause the apparent diameter to be much larger than the continuum diameter. We find that a warm molecular envelope model extending to ≈ 2.2 stellar radii can reproduce the observed uniform-disk diameters between 8 and 10 micron, and the observed increase of the uniform-disk diameter longward of 10 micron can be explained by an optically thin dust shell consisting of silicate and corundum grains.

Rotational evolution of VLM objects and brown dwarfs

Jochen Eislöffel (Thüringer Landessternwarte, Tautenburg)
Alexander Scholz (Thüringer Landessternwarte, Tautenburg)

The regulation of angular momentum is one of the key processes for our understanding of stellar evolution. The rotational evolution of a solar-mass star is mainly determined by the magnetic interaction with the circumstellar disk and angular momentum loss through stellar winds, and depends thus critically on the properties of the magnetic field of the star. For solar-mass stars, hundreds of rotation periods have been measured,which set strong constraints for models of rotational evolution. However, we are lacking a comparable database for very low mass (VLM) objects, i.e. brown dwarfs and stars with masses below 0.4 solar masses. In contrast to more massive stars, these VLM objects are believed to be fully convective. This may lead to major differences in terms of rotation and activity, since fully convective objects cannot host a solar-type dynamo.
Here we report on our observational efforts to understand the rotational evolution of VLM objects. By means of photometric monitoring, we determined 80 rotation periods for targets in five clusters, which form an age sequence from 3 to 750 Myr. We find that VLM objects rotate faster than their solar-mass siblings in all evolutionary stages. Their rotational evolution is determined by the hydrostatic contraction and exponential angular momentum loss, whereas the influence of the disk is not significant. The photometric amplitudes of the lightcurves are much lower than for more massive stars. This may be explained as a consequence of symmetric spot distributions and low contrast between spots and their environment. Most of these results can be explained with a change of the magnetic field properties with decreasing mass. VLM objects probably exhibit only small-scale, turbulent magnetic fields.

X-rays, pre-main sequence Stars and Planet Formation

Eric Feigelson (Penn. State)
X-ray studies have shown that late-type stars exhibit their highest levels of magnetic activity during their pre-main sequence phases. We present new observational results on this activity from the Chandra Orion Ultradeep Project which provides 2-week long lightcurves of 1600+ stars in the Orion Nebula. We show examples of the flaring behaviour, and discuss the evolution of magnetic activity from 10⁶ to 10¹⁰ years. The talk ends with an overview of possible effects of the X-rays on circumstellar material, particularly the protoplanetary disk. It is possible that X-ray ionization plays an important role in disk evolution and planet formation.

Detection of FIP effect in late-type giants

David Garcia-Alvarez (Harvard-Smithsonian CfA)
Jeremy J. Drake (Harvard-Smithsonian CfA)
LiWei Lin (Harvard-Smithsonian CfA)

We present an analysis of high resolution Chandra spectra of late-type giant stars. Our sample represents different giant evolutionary stages: the Hertzsprung gap (31 Com), the rapid braking zone (µ Vel) and the core helium burning ''clump'' phase (β Ceti). Using a new technique based on the ratios of prominent lines of highly ionized Fe and resonance lines of He-like and H-like ions, we have determined the temperature structure and chemical composition of the emitting plasma in their coronae. The temperature structures of both β Ceti and µ Vel are remarkably similar, showing a plateau around log T∼6.8. 31 Com is slightly hotter with a clear peak at log T=7.0. All three stars show evidence for a FIP effect in which low first ionization potential (FIP) elements (<10 eV) appear enhanced relative to high FIP elements (>10 eV). This trend is more obvious for β Ceti and µ Vel. We find that we can reproduce quite closely the X-ray spectrum of the clump + and Hertzsprung gap binary Capella by adding the spectra of β Ceti and 31 Com whose evolutionary phases and spectral types match quite closely those of the Capella binary components.

Accretion channeling in classical T Tauri stars.

Scott Gregory (University of St. Andrews, U.K.)
Moira Jardine (University of St. Andrews, U.K.)
Andrew Collier-Cameron (University of St. Andrews, U.K.)

It is now accepted that accretion in classical T Tauri stars is controlled by the stellar magnetosphere, as opposed to the traditional disc boundary layer model. The magnetosphere truncates the disc at several stellar radii allowing the disc material to couple to the field and fall toward the star; terminating in a shock at the photosphere. Observations suggest that the flow must hit the star at several hundred km/s. Using simple models of accretion to a dipole we shall demonstrate that the field structure does have an important role in controlling the accretion process. We also outline the first steps towards modelling accretion flows with magnetic field topologies with a realistic degree of complexity.

FUSE spectroscopy of Cool Stars

Graham M. Harper (CASA University of Colorado at Boulder)
Far Ultraviolet Spectroscopic Explorer (FUSE) results will be presented which provide insights into the atmospheric structure, activity and winds of young pre-mainsequence stars through to ancient evolved giants. FUSE, launched in June 1999, continues to provide a window into the 912-1187 Å region of cool star spectra, with a resolution of R=15,000 (20 kms^-1) and a peak effective area of 50 cm². FUSE spectra of coronal stars show solar-like transition region emission including the O VI resonance doublet and the pressure sensitive ratio of C III 977 Å. to the 1175 Å. multiplet. For active stars FUSE can also provide a link to coronal dynamics through the optically thin [Fe XVIII] 974 Å and [Fe XIX] 1118 Å. lines formed near 6 MK. Fluorescent Fe II and H₂ Lyman and Werner emission provides diagnostics of cooler plasmas and the H Lyman line radiation field, otherwise obscured but the ISM. Absorption from molecular hydrogen also provides a sensitive probe of H₂ and its distribution around young stellar systems. Finally, a brief status report on FUSE will be provided.

Rain and clouds in brown dwarf atmospheres: a coupled problem from small to large

Christiane Helling (Sterrewacht Leiden/Zentrum für Astronomie & Astrophysik, TU Berlin)
Peter Woitke (Sterrewacht Leiden)

The large scale structure of a brown dwarf atmosphere is determined by an interplay of convection, dust formation and its gravitational settling thereby providing also a possible cause of variability. The result is an element depletion of the dust forming regions and an element enrichment of the dust evaporating sites. The formation of dust cloud structures in substellar atmospheres will be demonstrated based on a consistent theoretical description of dust formation and destruction, gravitational settling, and element depletion including the effect of convective overshoot thereby overcoming the widely used concept of ad hoc dust presents in substellar atmospheres. Results of the calculation are e.g. the mean size of the dust particles and the element depletion which both vary with atmospheric height.
On the other hand side, every convectively instable gas may be turbulent if its viscosity is small thereby providing a source of small scale variability. Since the viscosity is small in brown dwarf atmospheres, the dust will have to form from a turbulent gas. Hence, the classical turbulent closure problem needs to be tackled in connection with dust formation also in substellar objects, because a complete three-dimensional and time-dependent solution of the model equations is simply not possible. Furthermore, structure formation may be seeded on the smallest scales, especially if chemical processes are involved. In order to understand the interaction of turbulence and dust formation, we have performed investigations of the smallest scale regimes in 1D and in 2D in order to identify the governing processes of the unresolved scale regime. From our multi-dimensional simulations, we deduce important demands on subgrid models from our results as important ingredients for a new generation of atmosphere simulations. We will further comment on a possible scaling into the observational regime.
http://www-astro.physik.tu-berlin.de/~chris/

Winds of cool Giant Stars

Susanne Hoefner (Dept. of Astronomy & Space Physics, Box 515, SE-75120 Uppsala, Sweden)
Cool giant stars are highly dynamical objects, and complex micro-physical processes play an important role in their extended atmospheres and winds. Both, theoretical studies of the mechanisms and effects of mass loss, as well as interpretations of observations, require realistic self-consistent models of the atmospheres and winds of AGB stars. Current dynamical models of these stars include quite detailed micro-physics, and the resulting synthetic spectra compare reasonably well with observations. Recent advances and trends in this field will be discussed.

Activity cycles and polar caps on solar-like stars

Moira Jardine (School of Physics and Astronomy, St Andrews)
Duncan MacKay (School of Mathematics and Statistics, St Andrews)
Gaitee Hussain (ESTEC)

While the Sun produces spots at low to intermediate latitudes, it has been known for some time now that more rapidly-rotating stars have spots at much higher latitudes, even extending up to the rotation pole. For the most rapid rotators, we can determine the surface magnetic polarities from Zeeman-Doppler imaging. While a solar model of flux emergence and transport would predict that the high-latitude flux should be unipolar, Zeeman-Doppler images show it to be of mixed polarity. In order to determine how such a flux distribution might arise, we have modelled the surface field evolution of a rapid rotator as new bipoles emerge and are transported by differential rotation, meridional flow and supergranular diffusion. To produce the observed high-latitude intermingling of flux, the latitude at which flux emerges through the surface must be increased to values of 50 to 70 degrees and the meridional flow must be increased by a factor of 10 over the solar value to around 100 m/s.
http://star-www.st-and.ac.uk/~mmj/

Exploring Brown Dwarf Origins

Ray Jayawardhana (University of Michigan )
Brown dwarfs, which straddle the mass range between stars and planets, appear to be common both in the field and in star-forming regions. Their ubiquity makes the question of their origin an important one, both for our understanding of brown dwarfs themselves as well as for theories on the formation of stars and planets. I will discuss recent results that provide valuable clues to the formation and early evolution of sub-stellar objects. In particular, observations of disk frequency and characteristics and measurements of accretion signatures confirm that young brown dwarfs undergo a T Tauri-like phase similar to that of low-mass stars.
http://www.astro.lsa.umich.edu/~rayjay

The solar chromosphere and corona during the Maunder minimum

Philip Judge (High Altitude Observatory, National Center for Atmospheric Research)
Steven H. Saar (Harvard-Smithsonian Center for Astrophysics)

The Maunder Minimum (1645--1715) is the only documented period in which a correlation between climate and solar magnetic activity has been found. Very few sunspots were observed, nearly all of them in one hemisphere, and yet ¹⁰Be ice core records indicate modulation of cosmic rays by heliospheric magnetic fields. For its own sake, and also to try to understand more concerning the solar magnetic field in this period, we ask, what was the state of the Sun's chromosphere and corona during this period? To address this question, we have carefully compared solar UV emission from the SoHO spacecraft with similar data of particular "flat activity" stars from the Hubble Space Telescope, and solar X-ray emission from the SNOE spacecraft with data from the ROSAT archive. Assuming that flat activity dwarf stars are in the stellar equivalent of a solar Maunder Minimum, we conclude that the radiative output of the Sun's chromosphere and corona were similar to those observed under conditions close to current solar minima. We speculate on the nature of the solar magnetic field during the Maunder minimum, based on these results, and discuss some directions for further research.

New insights into Solar Physics from RHESSI

Säm Krucker (Space Sciences Lab University of California Berkeley)
the RHESSI team

The Reuven Ramaty High Energy Solar Spectroscopic Imager (RHESSI) is the sixth in the NASA line of Small Explorer (SMEX) and is designed to investigate particle acceleration and energy release in solar flares, through imaging and spectroscopy of hard X-ray/γ-ray continua emitted by energetic electrons, and γ-ray lines produced by energetic ions. Since launch on 5 February, 2002, the RHESSI has recorded well over 10,000 X-ray flares and 6 γ-ray line flares. Major results will be reviewed including 3-15 keV microflare observations, evidence for the generation of current sheets during impulsive X-ray flares, HXR source motions during flares and their implication for magnetic reconnection models, first high-resolution γ-ray line spectroscopy, and first imaging of γ-ray lines.
http://hessi.ssl.berkeley.edu/

Spatially resolved STIS spectra of Betelgeuse's upper chromosphere and circumstellar dust envelope

Alex Lobel (Smithsonian Astrophysical Observatory)
We highlight recent observations of Betelgeuse's outer atmosphere, providing strong evidence for warm chromospheric plasma far inside the red supergiant's extended Circumstellar Dust Envelope (CDE). The new spatially resolved HST-STIS spectra directly demonstrate, for the first time, that gas outflow in its upper chromosphere accelerates with larger distance from the surface.
A prominent increase in asymmetry of detailed line profiles of Mg II h & k emission lines directly demonstrates that the warm chromospheric wind extends far beyond the dust condensation radius determined from stationary dust-driven wind acceleration models.
The recent STIS data can therefore support the dust-gas interaction driving mechanism, yielding the high mass-loss rates observed in cool supergiants and AGB stars. From a thermodynamic point of view however, the uniform dusty wind model fails to account for the large local kinetic gas temperature differences because the warm chromospheric gas (T_gas ≥ 2600 K) is observed far inside the CDE (T_dust ≤ 600 K), out to 3, ca. 120 R_⋆ (1 R_⋆ ≈ 700 R) away from Betelgeuse.
http://cfa-www.harvard.edu/~alobel http://alobel.freeshell.org

Status and future of hydrodynamical model atmospheres

Hans-Günter Ludwig (Lund Observatory, Sweden)
Arunas Kucinskas (Lund Observatory, Sweden/Institute of Theoretical Physics and Astronomy, Vilnius, Lithuania)

Since about 25 years work has been dedicated to the development of hydrodynamical model atmospheres for cool stars (of A to T spectral type). Despite their obviously sounder physical foundation in comparison with standard hydrostatic models, their general application has been rather limited. In order to understand why this is, and how to progress, we review the present status of hydrodynamical modelling of cool star atmospheres. The development efforts were and are motivated by the theoretical interest of understanding the dynamical processes operating in stellar atmospheres. To show the observational impact, we discuss examples in the fields of spectroscopy and stellar structure where hydrodynamical modelling provided results on a level qualitatively beyond standard models. We stress present modelling challenges, and highlight presently possible and future observations that would be particularly valuable in the interplay between model validation and interpretation of observables, to eventually widen the usage of hydrodynamical model atmospheres within the astronomical community.
http://www.astro.lu.se/~hgl

Spitzer observations of brown dwarf disks

Kevin Luhman (Smithsonian Astrophysical Observatory)
Giovanni Fazio (Smithsonian Astrophysical Observatory)
Lee Hartmann (Smithsonian Astrophysical Observatory)

Through the Spitzer IRAC GTO program, we have recently obtained extremely sensitive mid-infrared images of young brown dwarfs in the nearest star-forming regions. The spectral energy distributions measured from these data provide unprecedented measurements of the structure and lifetimes protoplanetary disks around young brown dwarfs down to 10 times the mass of Jupiter.

Sub-mm continuum emission from Class 0 sources: Theory, Observations, and Modelling

Rengel Lamus Miriam (Thueringer Landessternwarte Tautenburg, Sternwarte 5, D-07778 Tautenburg, Germany)
Hodapp K.W (University of Hawaii, Institute for Astronomy, 640 N. A'ohoku Place Hilo, HI 96720 USA)
Froebrich D., et al. (Dublin Institute for Advanced Studies, 5 Merrion Square, Dublin 2, Ireland )

The earliest evolutionary phase of star formation, in which a deeply embedded protostar is known to exist, is the so-called Class 0 stage (André et al. 1993). Because protostars in this phase, Class 0 sources, are difficult to observe, constraining physical properties of Class 0 sources is an effortful task. We present sub-mm continuum observations and modelling results of the temperature and the spectral energy distributions (SEDs), and of the radial intensity profiles of nine Class 0 sources. SCUBA observations of thermal dust emission of envelopes of Class 0 sources in Orion and Perseus, a model of the circumstellar envelope, the implementation of the blackbody fitting technique, the 1D MC3D radiative transfer code (Wolf 2002), and an protostellar evolutionary scheme (Smith 2002) provide a way to interpret the structure of Class 0 sources, and to estimate their physical properties in an evolutionary context. The gas and dust temperature distribution as function of the radius T ∝ r^-q with q=0.4 is reproduced for the sample. Nevertheless, the temperature distribution departs from this value in the inner envelope (< 10 AU), perhaps caused by thermal convection in this region. The power-law index p of the density distribution ρ (r) ∝ r^-p spans a range of 1.5-2, which is predicted by all of the collapse models and the numerical studies. A sublimation radius of 3-5 AU is found, which is roughly the same as the radius of the photosphere (because the gas that is accreted close to the central object is optically thick, the central source should radiate from this specific radius, where the layer changes between the optically thick and the thin regime) at 450 and τ=1 if p=2 (ca. 10 AU for p=1.5). A detailed comparison between observed and modeled SEDs and radial profiles of the sample shows that the assumption of spherical symmetry is reasonable. Finally, the observed sources are surrounded by envelopes with masses of about 1-6 solar masses and sizes between 3000-10000 AU. For the sample of Class 0 sources, the model-dependent ages are in a range from 10 to 30 thousand years. The envelope density structure of Class 0 sources apparently evolves from ρ ∝ r^-2 at younger ages, to a ρ ∝ r^-3/2 at later times.
http://www.tls-tautenburg.de/research/mrengel/index.html

Fundamental parameters of young brown dwarfs: surface gravity, masses and radii from high-resolution spectroscopy

Subhanjoy Mohanty (Harvard-Smithsonian Center for Astrophysics, USA)
Ray Jayawardhana (University of Michigan, USA)
Gibor Basri (University of California at Berkeley)

We present an analysis of high resolution optical spectra for a sample of very young, mid- to late M, low-mass stars and brown dwarfs. Effective temperatures and surface gravities are derived from a multi-feature spectral analysis, through comparison with the latest synthetic spectra. Masses, radii and luminosities are then inferred by combining the temperatures and gravities with observed photometry, synthetic surface fluxes and distance information. Crucially, our analysis is independent of theoretical evolutionary models and isochrones, and thus serves as a test of the latter.
We find that: (1) Our gravities and inferred mass-radius and mass-luminosity relationships agree remarkably well with the isochrone predictions for the likely cluster ages for most of the sample. However, (2) the coolest objects have gravities much lower, and radii and luminosities significantly higher, than predicted. (3) Moreover, two of our coolest late-M targets appear to have masses close to the deuterium-fusion boundary, much lower than the evolutionary models suggest.
These results indicate that (1) current evolutionary models might have significant uncertainties for very young, cool ultra-low mass objects, arising from an inadequate treatment of accretion, convection and/or deuterium-burning effects. Moreover, (2) the faintest late-M objects may be substantially lower in mass than previously thought: free-floating bodies close to or below the planetary-mass boundary may not be very rare.

X-rays of stellar Coronae with Chandra and XMM-Newton: densities and structures in stellar coronae

Jan-Uwe Ness (Hamburger Sternwarte)
The investigation of coronal properties for magnetically active stars is presently pushed forward by high-resolution X-ray spectroscopy. The measurement of electron densities can only be carried out by measurement of individual emission lines produced or suppressed by collisions. The X-ray gratings on board XMM-Newton and Chandra provide sufficient spectral resolution and sensitivity to measure such lines. Prior to these missions density sensitive lines in the UV range, measured with, e.g., EUVE, have been used to constrain electron densities. I will summarize the EUVE measurements of density sensitive lines and contrast the results with new Chandra and XMM-Newton results. Many coronal sources have been observed with at least one of the X-ray grating instruments. I gathered all these spectra and measured the density sensitive lines. With such a large survey general statements on coronal structures can be made. I will use basic scaling laws in order to demonstrate the power of density measurements in a large sample.
http://www.hs.uni-hamburg.de/DE/Ins/Per/Ness

The Age Activity Rotation relationship in solar type stars

Giancarlo Pace (European Southern Observatory)
Luca Pasquini (European Southern Observatory)

Measured from high resolution spectra, we present Ca II K line chromospheric fluxes in 35 G dwarf stars of 5 open clusters to determine age--activity--rotation relationship at intermediate and old ages. The clusters encompass a wide range of ages, from the young Hyades and Praesepe (0.6 Gyr) to the old M67 (≈ 4.5 Gyr) through the two intermediate age clusters IC 4651 and NGC 3680 (≈ 1.7 Gyr). The full variation of the activity index within a cluster is slightly above 60 % for every cluster but one, NGC3680, in which only two stars were observed. As a comparison, the same Solar Ca II index varies by ≈ 20 % during a solar cycle. This result indicates that a long term variability about 3 times in excess of the present solar cycle may be present even in stars as old as the sun. Four of our clusters (Hyades and Praesepe, IC4651 and NGC3680) are couple of twins as far as age is concerned; the Hyades have the same chromospheric activity level than Praesepe, at odds with early claims based on X--ray observations, and NGC3680 and IC4651 are indistinguishable, as far as chromospheric activity is concerned. This confirms beautifully the existence of and age-activity relationship. On the other hand, the two intermediate age clusters have the same activity level of the much older M67 and of the Sun. Our data therefore shows that a dramatic decrease in chromospheric activity takes place among solar stars between the Hyades and the IC4651 age, in about 1 Gyr. Afterwards, activity remains virtually constant for more than 3 Gyr. We have also measured (v sini) for all our stars and the average rotational velocity shows the very same trend as the chromospheric activity index. We briefly investigate the impact of this result on the age determinations of G stars; the two main conclusions are that a consistent group of 'young' stars (e.g. younger than 0.6 Gyr) is present in the solar neighborhood, and that it is virtually impossible to give accurate chromospheric ages for stars older than ≈ 2 Gyr. The observed abrupt decline in activity explains very well the Vaughan-Preston gap.

The Formation of low mass stars

Francesco Palla (Osservatorio Astrofisico di Arcetri Firenze, Italy)
The processes that lead to the formation and early evolution of low mass stars are in a broad sense well understood theoretically and carefully traced observationally. The largest uncertainties in this framework still reside in the initial conditions for gravitational collapse inside dense molecular cores. In this review, I will cover three topics: the evidence for an accelerated pattern of star formation in clusters and associations, the physical origin of this phenomenon, and the age spread of low-mass star forming regions. On the latter issue, I will show how the observation of lithium depletion in young clusters, such as the Orion cluster and the Upper Scorpius association, can provide an independent estimate of their ages.

Tackling the coronal heating problem using 3D MHD coronal simulations with spectral synthesis

Hardi Peter (Kiepenheuer-Institut für Sonnenphysik, Freiburg, Germany)
Boris Gudiksen (Institute for Theoretical Astrophysics, University Oslo, Norway)
Åke Nordlund (Astronomical Observatory, NBIfAFG, Copenhagen University, Denmark)

The lower corona and transition region of the Sun are highly structured and very dynamic. To account for both the structure and the dynamics one has to apply a time-dependent three-dimensional model description. Recently Gudiksen and Nordlund (2002) succeeded in constructing such a 3D MHD model for an active region with the heating being due to braiding of magnetic flux.
We have now calculated spectra of prominent EUV emission lines from these model calculations and compared them to observations. The main result from this study is that the flux-braiding heating is resulting in the right differential emission measure (DEM) curve, i.e. we can reproduce the increase of DEM for low temperatures, without any spurious assumptions. Furthermore the Doppler shifts of the synthesized lines match the observed Doppler shifts strikingly well.
To our knowledge this is the first model to reproduce the DEM and Doppler shift variations with temperature qualitatively and quantitatively. It also provides a unique tool to explore stellar coronae by changing the boundary conditions, in particular the photospheric magnetic field and velocity structure.

Spectroscopic characteristics of extra-solar Planets and their Host-Stars

Nuno Santos (Lisbon Observatory/CAAUL)
Current surveys have already revealed about 120 extra-solar planets orbiting solar-type stars. The discovered planets present a wide variety of orbital elements and masses, which have raised many problems and questions regarding the processes involved in their formation and evolution.
One particular fact that is helping us to understand the mechanisms of planetary formation has to do with the planet host stars themselves. In fact, these were found to have, in average, a metal content higher than in stars without detected planetary companions. The most recent studies seem to favor that this metallicity ``excess'' is originally from the cloud that gave origin to the star/planetary system, and thus favour a scenario where planet formation is more efficient in metal-rich environments.
In this talk we will mainly focus on the most recent results on the chemical abundances of planet-host stars, and what kind of information they are bringing.

Coronal heating and the appearance of solar and stellar coronae

Carolus J. Schrijver (Lockheed Martin Advanced Tech. Ctr., USA)
Anne W. Sandman, Markus J. Aschwanden, Marc L. DeRosa

We constrain the properties of the mechanism(s) responsible for the bulk of the heating of the corona of the Sun by simulating the appearance of the entire solar corona and by comparing these results directly to observations. The best fit has a heating flux density through the coronal base that scales as F_H ≈ 4 × 10¹⁴ B^{1.0 ± 0.3}/L^{1.0± 0.5} (in erg/cm²/s, for the base field strength B in Mx/cm² and loop half length L in cm), while allowing for loop expansion with height, and for a heating scale height that is at least a sizeable fraction of the loop length. This scaling for coronal heating points to DC reconnection at tangential discontinuities as the most likely coronal heating mechanism, provided that the reconnection progresses proportional to the Alfvén velocity. This scaling for coronal heating appears to be compatible with radiative losses from stellar coronae for Sun-like stars up to activity levels that exceed that of the Sun by at least an order of magnitude. We show simulated coronal images for stars of various levels of activity, including those that earlier modeling suggested to have high-latitude or polar starspots.

Solar activity over the last 1150 years: does it correlate with climate?

Sami K. Solanki (MPI für Sonnensystemforschung, Katlenburg-Lindau, Germany)
Ilya Usoskin (Sodankyla Geophysical Observatory, University of Oulu, Finland)
Manfred Schuessler (MPI für Sonnensystemforschung, Katlenburg-Lindau, Germany)

The sunspot number is the longest running direct index of solar activity, with reliable measurements starting in 1610. For many purposes it needs to be extended, however. This would benefit, in particular, from comparisons with climate indices. We present a reconstruction of the cycle averaged sunspot number over the last millennium based on ¹⁰Be concentrations in Greenland and Antarctic ice. We expect this reconstruction to be close to an upper limit to the correct sunspot numbers, particularly for the earlier times. Our reconstruction agrees very well with the direct measurements during the last 3 centuries (although the values are slightly higher during the Maunder minimum). The full reconstructed sunspot number series shows all the known Grand Minima (Maunder, Spoerer, Wolf, etc.) and the medieval maximum. However, the most striking feature of the reconstruction is that during the last 1150 years the Sun was never as active as during the last 60 years. We present a comparison with the Mann et al. "hockey stick" curve for global temperature and find a reasonable correspondence, if we neglect the last 2 decades. In particular the sunspot number exhibits a gentle decreasing trend over most of this period followed by a rapid increase in the last century. During the last 2 decades, however, the cycle-averaged sunspot number has remained basically constant, while the temperature has continued to increase.
www.linmpi.mpg.de/~solanki

The 2002 Outburst of V838 Mon: An L Supergiant and a Light Echo

Sumner Starrfield (Department of Physics and Astronomy, Arizona State University, USA)
Howard Bond (STScI)
R. Mark Wagner (LBT Observatory)

Several well-known classes of stars, including supernovae and novae, undergo explosive outbursts that eject stellar material into space. The previously unknown variable star V838 Mon erupted in early 2002, brightening suddenly by a factor of ten thousand. Unlike a supernova or nova, V838 Mon did not explosively eject its outer layers; instead, it simply expanded to become a cool supergiant. A set of light echoes was discovered around the star shortly afterward, as illumination from the outburst propagated into surrounding, pre-existing circumstellar dust. Here we report high-resolution imaging and polarimetry of the light echoes. Two novel methods applied to these images allow us to set direct geometric limits on the distance to the object and its luminosity. The large distance (> 6,000 parsec) implies that V838 Mon was extremely luminous: indeed, temporarily the brightest star in the Milky Way. V838 Mon represents a new class of stellar outbursts whose underlying mechanism is at present unknown.
http://hubblesite.org/newscenter/newsdesk/archive/releases/2003/10/

New Cool Star science with the Spitzer Space Telescope

John Stauffer (Spitzer Science Center )
NASA launched the Spitzer Space Telescope (formerly known as SIRTF) in August 2003. As of the time of CSW13, Spitzer will have been taking data in its ``normal operations'' phase for nearly eight months. Mission lifetime (set primarily by the cryogen use rate) is now expected to be at least five years. Spitzer has three science instruments: a near-IR camera - IRAC - with four channels (3.6, 4.5, 6.0 and 8.0 µm); a mid-IR camera - MIPS - with three channels (24, 70 and 160 µm); and a spectrograph - IRS (operating from about 5 to 37 µm). Observations obtained through July 2004 have been primarily from programs defined by the three instrument teams and the science-working-group members (``Guaranteed'' time observers) and by six ``Legacy Science'' teams chosen well-prior to launch. I will describe Spitzer observations that have been obtained by these groups for cool stars and stellar systems, and Furthermore, I will briefly describe more generally how the Spitzer instruments are performing and plans for future guest-observer cycles.

Multi-wavelength study of X-ray emitting A- and B-stars testing the companion hypothesis

Beate Stelzer (INAF -- Osservatorio Astronomico di Palermo)
No mechanism is known that produces X-rays in late B-type and early A-type stars: they are not massive enough to drive strong stellar winds, nor do they possess convective zones that could sustain a magnetic dynamo. Nevertheless their detection has been reported from virtually all X-ray satellites, and has remained a mystery to date. We use a multi-wavelength approach to test the most wide-spread hypothesis that the X-rays are generated by late-type magnetically active companions. Our high spatial resolution observations of A/B-type stars in the IR using adaptive optics uncover hypothetical companion stars at arcsecond separations from the primary. Chandra's unprecedented spatial resolution allows to pinpoint the location of the X-ray emission in the same targets. Finally, with IR spectroscopy of the A/B-type stars still detected with Chandra we search for temperature sensitive features indicating the existence of even closer cool companions. Even with this multi-fold strategy we are likely to miss the closest of the possible companions, but a study of the X-ray properties can provide further information on the nature of the emitters.

Detection of X-ray resonance scattering in active stellar coronae

Paola Testa (Universita' di Palermo)
Jeremy J. Drake (Smithsonian Astrophysical Observatory)
Giovanni Peres (Universita' di Palermo)

We have analyzed high-resolution X-ray spectra of a sample of 22 active stars observed with the High Energy Transmission Grating Spectrometer on Chandra in order to investigate the properties of optical thickness of the coronal plasma. The analysis of Lyman series lines arising from hydrogen-like oxygen and neon ions shows in the coronae of the active RS CVn-type binaries II Peg and IM Peg significant decrements in the Lyα/Lyβ ratios as compared with theoretical predictions and with the same ratios observed in similar active binaries. We interpret these depletions in terms of resonance scattering of line photons out of the line-of-sight; these observations present the first strong evidence for this effect in active stellar coronae. The net line photon loss implies a non-uniform and asymmetric surface distribution of emitting structures on these stars. Escape probability arguments imply typical line-of-sight sizes of the coronal structures that dominate the X-ray emission of 10¹⁰ cm at temperatures of 3MK and 10⁸ cm at ∼ 10MK. These sizes are an order of magnitude larger than predicted by simple quasi-static coronal loop models, but are still very small compared to the several 10¹¹ cm radii of the stars.

Magnetic Field measurements for Cool Stars

Jeff Valenti (STScI)
Christopher Johns-Krull (Rice University)

In principle, observations of surface magnetic fields on cool stars can provide an upper boundary condition on stellar dynamo models and a lower boundary condition on coronal heating models. In practice, the spectroscopic signatures of surface magnetic field can be quite subtle.
However, infrared spectrographs with high resolution and high sensitivity are now yielding clear signatures of Zeeman broadening in young stars, which have surprisingly strong magnetic fields. Circular spectropolarimetry is also starting to provide new constraints on surface magnetic fields.
We will show examples of Zeeman broadening in key spectral lines at 0.86, 0.99, 1.56, and 2.22 microns, indicating which diagnostic is best as a function of spectral type. We will also show time series spectropolarimetry for T Tauri stars that constrains magnetic geometry at the stellar surface, globally and in accretion footpoints. Finally, we will discuss opportunities for using and improving stellar magnetic field measurements.

Turning cool star X-ray spectra upside down

Klaus Werner (University of Tübingen, Germany)
J.J. Drake (Center for Astrophysics, Cambridge, USA)

H1504+65 is a young white dwarf with a temperature of 200,000 K and is the hottest post-AGB star ever analysed with detailed model atmospheres. Chandra LETG+HRC-S spectra have revealed the richest X-ray absorption line spectrum recorded from a stellar photosphere to date. The line forming regions in this extremely hot photosphere produce many transitions in absorption that are also observed in emission in cool star coronae. We have performed a detailed comparison of Chandra spectra of H1504+65 with those of Procyon and alpha Cen A and B. State of the art non-LTE model spectra for the hot white dwarf have enabled us to identify a wealth of absorption lines from highly ionised O, Ne and Mg. In turn, these features have allowed us to identify coronal lines whose origins were hitherto unknown.

Winds of solar-like main-sequence Stars

Brian Wood (University of Colorado)
It has recently become possible to study solar-like coronal winds around other stars by detecting their interactions with the interstellar medium. The wind/ISM interaction regions are called "astrospheres," analogous to the "heliosphere" surrounding the Sun. Both the heliosphere and astrospheres contain a population of hot hydrogen gas created by the wind/ISM collision. This H I gas produces a substantial amount of absorption in stellar Lyman-alpha lines observed by the Hubble Space Telescope (HST), and the Lyman-alpha absorption diagnostic has led to numerous measurements of mass loss rates for nearby solar-like stars. I will report on several new detections of astrospheric and heliospheric absorption found in the HST archives, and I will discuss the implications of these detections for our understanding of how winds vary with stellar age and activity.
http://origins.colorado.edu/~woodb

Posters

Why do some spotted stars become bluer as they become fainter?

Vidar Aarum-Ulvås (Astrophysikalisches Institut Potsdam An der Sternwarte 16 D-14482 Potsdam Germany)
Gregory W. Henry (Tennessee State University)

Chromospherically active, spotted stars generally become redder as well as fainter when large starspots rotate into view on the stellar disk. However, the RS CVn system UX Ari (a triple-lined system), becomes bluer as it gets fainter. One possible explanation is that hot, bright regions accompany the cool, dark spots on the surface of the active component. The bluer flux of the hotter, inactive component does not appear to be sufficient to explain the observed behaviour. We have begun a search for additional chromospherically active stars with a similar relation between colour and brightness. The first results are presented here, and we investigate possible explanations.

FUSE Observations of Atmospheric Eclipsing Binaries

Thomas Ake (Johns Hopkins University/Computer Sciences Corporation)
Richard Robinson (Johns Hopkins University/Computer Sciences Corporation)

We have obtained FUSE observations of the zeta-Aur systems 22 Vul and HR 6902 near and at primary eclipse. These systems are comprised of a G-type luminous primary star and a late B-type main sequence companion, which can be used as a probe of the outer atmosphere of the G star during partial eclipse phases. The G stars are on different sides of the dividing line between coronal and non-coronal stars.
These stars are quite different in the FUSE wavelength region. During primary eclipse, the spectrum of 22 Vul is dominated by low-lying emission lines, such as Fe II and C II, caused by resonance scattering of the B star photons in the cool star wind. More surprisingly, it also shows a pronounced self-reversed emission in O VI. This indicates the presence of 300 000K plasma on the G star and suggests that it may be a hybrid. Outside of eclipse, 22 Vul shows numerous absorption features from the G star wind, possibly including an O VI absorption, superimposed on the B star spectrum. In contrast, HR 6902 shows no high temperature lines and the wind-scattered lines at totality are weak. However, the diagnostic lines may be masked by the strong H₂ absorption in this system.

A Comprehensive Search for Wide Ultra-Cool Companions

Peter Allen (University of Pennsylvania)
To date all ultra-cool dwarf binaries discovered have small separations, <15AU.5 We present the preliminary results of a search for wide companions to low-mass stars and brown dwarfs. No wide brown dwarf binaries (20AU - 1000AU) have been found by our observations. Initial efforts to analyze our new observations and existing data with a robust Bayesian statistical approach are discussed. We find that the companion distribution is not well sampled; therefore, the possibility of wide brown dwarf-brown dwarf companions cannot be ruled out. We will explore methods to fully sample the wide companion distribution.

Abundances of Main-Sequence Stars in the Hyades and the Pleiades

Carlos Allende Prieto (University of Texas)
David Yong (University of Texas)
David L. Lambert (University of Texas)

Open clusters, in particular those nearby, have always been very valuable to inspire and test theories of structure, formation, evolution, and nucleosynthesis in stars. We revisit the chemical abundances along the main sequence of the Hyades and the Pleiades with improved data and analysis techniques.
http://hebe.as.utexas.edu/

High-resolution spectroscopy of the UMa group

Matthias Ammler (Astrophysical Institute and University Observatory Jena)
Klaus Fuhrmann (Max Planck Institute for Extraterrestrial Physics)
Eike Guenther (Thüringer Landessternwarte Tautenburg)

We are presenting a project to analyse homogeneously Ursa Major (UMa) group members and candidates based on high-resolution, high-signal-to-noise spectroscopy in the optical wavelength regime. The members of the UMa open cluster and a large number of additional stars form the UMa group with membership assignments still being under dispute. Though all stars show common overall properties, e.g. distinct kinematics, the assessment of firm membership criteria is difficult. Additionally, we just know that the age of the stars is young but age determinations range widely from 100 to 500 Myrs. Spectra of a large sample of UMa group members and candidates will enable us to address those questions homogeneously and in detail. The spectra not only provide equivalent widths of lines, which are used as age and activity indicators but also allow us to analyse the stellar atmospheres in more detail. This has not been done so far for a larger sample of UMa group members. Taking into account information found in the literature, we intend to assess membership criteria, nature and age of the UMa group more precisely than before.

Better Distances to Open Clusters through Calibrated Isochrones

Deokkeun An (Ohio State University, USA)
Donald M. Terndrup (Ohio State University)
Marc H. Pinsonneault (Ohio State University)

We present a progress report on our efforts to improve the empirical calibration of theoretical isochrones using metallicities and colors of nearby field stars and clusters. We confirm recent work suggesting that several widely-used color-temperature (C-T) relations have significant systematic errors, and propose a new C-T relation valid for combinations of B, V, Cousins I, and 2MASS JHK photometry. Finally, we present new multicolor photometry of spotted variable stars to explore the causes of the significant departures from the Hyades lower main sequence seen in the photometry of young star clusters.
http://www.astronomy.ohio-state.edu/~deokkeun/

High Resolution X-ray Spectroscopy of Pre-Main-Sequence Stars

Costanza Argiroffi (Universita' di Palermo Piazza del Parlamento 1, 90134 Palermo, Italy)
We report on the analysis of high resolution X-ray spectra of the pre-main-sequence star PZ Telescopii, a rapidly rotating post-T Tauri star in the Tucana association, observed with Chandra/HETGS. We have reconstructed the emission measure distribution and we have derived coronal abundances to check for possible patterns of the abundances related to the First Ionization Potential of the various elements. We have also derived estimates of the plasma density from the analysis of the He-like triplets. For comparison purposes we present also preliminary results of the analysis of XMM/RGS spectra of TWA 5 a classical T Tauri star in the TW Hydrae association. We compare the characteristics of our targets with those of the classical T Tauri star TW Hydrae: the characteristic temperatures, abundances and densities derived from the X-ray emission of the stars we have analyzed are much more similar to those of main sequence active stars than to those of TW Hydrae itself. These results suggest that X-ray emission from T Tauri and post-T Tauri stars are produced by magnetically-heated coronae, but TW Hydrae shows a different behavior.

The Li overabundance of J37: Diffusion or Accretion?

Johanna Fleur Ashwell (Astrophysics Group, School of Chemistry & Physics, Keele University, Staffordshire, ST5 5BG, UK)
R.D. Jeffries, Barry Smalley (Astrophysics Group, Keele University, UK)
et al. ()

In September 2002 the discovery of a super Li-rich F-dwarf (J37) in NGC 6633, an iron poor analogue of the better studied Hyades and Praecepe open clusters, was announced. This, at the time, unique star was thought to be the smoking gun for the action of diffusion models which predict a narrow "Li-peak" at roughly the right temperature. However, with the recent discovery of similar stars in a number of open clusters of different ages, J37 may represent the first of a new class of star providing firm evidence of the accretion of planetesimals or other material from the circumstellar environment of new born stars.
Thanks to the specific predictions made about the behavior of Be abundances, (the most striking of which being we should see no Be in super-Li-rich dwarfs) the opposing diffusion/accretion predictions can be tested.
Using the UVES/UT2 combination we are measuring detailed abundances for many chemical elements Fe, Mn, Ti etc but most critically Beryllium.

A Multi-Wavelength Study of RZ Cassiopeiae: The XMM-Newton Campaign

Marc Audard (Columbia Astrophysics Laboratory)
M. Guedel (Paul Scherrer Institut)

XMM-Newton and the VLA simultaneously observed the eclipsing Algol-type binary RZ Cassiopeiae in August 2003. The secondary eclipse (K3 IV companion behind the A3 V primary) was placed at the center of the 15-hour radio campaign, while the X-ray satellite monitored a full 1.2 day orbital period. We present here preliminary results of the X-ray campaign with XMM-Newton. The X-ray light curve shows significant modulation probably related to rotational modulation, and even small flares. However, the X-ray eclipse is not deep, implying that the coronal X-ray emitting material is spatially extended. The Reflection Grating Spectrometer spectrum shows a variety of bright emission lines from Fe, Ne, O, N. However, the C VI Lya line is not detected. The strong [C/N] depletion probably reflects the surface composition of the secondary which fills its Roche lobe and loses material onto the primary. The O VII He-like triplet reflects a low forbidden-to-intercombination ratio; while it generally suggests high electron densities, the ratio is here modified by photoexcitation by the strong UV flux of the primary A3 V star.

High-Energy Processes In Young Stars: Chandra X-Ray Spectroscopy of HDE 283572

Marc Audard (Columbia Astrophysics Laboratory)
Steve Skinner; Kester Smith (CASA/Colorado; MPIfR)
Manuel Guedel; Roberto Pallavicini (Paul Scherrer Institut; Palermo Observatory)

Weak-lined T Tauri stars (WTTS) represent the important stage of stellar evolution between the accretion phase and the zero-age main sequence. At this stage, the star decouples from its accretion disk, and consequently spins up to a higher rotation rate than in the preceding CTT phase. Consequently, dynamo processes can be expected to be even stronger at this stage. High energy processes can have effects on the remaining circumstellar material, possibly including protoplanets and planetesimals, and these effects may account for certain observable properties of asteroids in the current solar system. Chandra has observed the WTTS HDE 283572 (G5 IV) which probes the PMS stage of massive A-type stars. We will present first results of the analysis of its high-resolution X-ray spectrum obtained with the HETGS. A wide range of Fe lines of high ionization states are observed, indicating a continuous emission measure distribution. No significant signal is detected longward of the O VII Lyalpha line because of the high photoelectric absorption. The X-ray spectrum will be compared to X-ray spectra of CTTS, other WTTS, and young main-sequence stars.

Procyon A Convection Signatures: An Analysis of Interferometric, Spectroscopic, and Photometric Data with PHOENIX Model Atmospheres

Jason Aufdenberg (National Optical Astronomy Observatory)
Pierre Kervella (LESIA, Observatorie de Paris-Meduon)
David Mozurkewich (Seabrook Engineering)

We present models for Procyon A (F5 IV) in comparison to K-band data from the VLTI/VINCI and CHARA/FLUOR interferometers and 500nm and 800nm data from the Mark III interferometer. Together these data sets provide the broadest wavelength dependent limb-darkening measurements of the photosphere to date. A best fit PHOENIX model atmosphere to Procyon's spectral energy distribution provides a satisfactory match to all the visibility data. Deviations of the visibility data from our model atmosphere predictions, though of low statistical significance, are consistent in direction and magnitude with that predicted by the 3-D convection model of Allende Prieto et al.(2002). Contrary to recent studies (e.g., Heiter et al. 2002), we find that 1) synthetic line profiles for H-beta and H-alpha are largely insensitive to the mixing-length value assumed in the convection treatment and 2) the mixing-length value of alpha=1.25 provides a better fit to spectral energy distribution than alpha=0.5. The latter result suggests an inconsistency between theoretical Strömgren color indices and spectrophotometry of Procyon.

CoolCAT: An HST/STIS Echelle Survey of Ultraviolet Emissions from Late-Type Stars

Thomas Ayres (CASA University of Colorado Boulder, CO, USA)
CoolCAT is a UV spectral survey of late-type stars based on the rich HST/STIS archive, comprising about 50 more-or-less normal cool stars. Echelle-mode observations were used exclusively: 210 E140M's (1150-1700 Angstroms; 40,000 resolution), and 159 E230's (1700-3200 Angstroms), split as 61 medium-res (M: R=30,000) and 98 high-res (H: R=110,000). CoolCAT consists, primarily, of digital spectral atlases. A supporting catalog provides line identifications, wavelength centroids, Doppler widths, and fluxes. A wide range of investigations--from the photochemical evolution of primitive planetary atmospheres, the dynamics of cool star chromospheres, to galactic population synthesis--will be enabled by CoolCAT. Here, I focus on a key objective of the survey: transition-zone line-width and Doppler shift trends, a topic relevant to coronal heating. This is by far the largest stellar UV sample brought to bear on this problem to date.
This work was supported by grant HST-AR-09550.01-A.
http://casa.colorado.edu/~ayres/CoolCAT

Optimal design of the Gaia photometric system for stellar parameterization using evolutionary algorithms

Coryn A.L. Bailer-Jones (Max-Planck-Institut fuer Astronomie Heidelberg)
Large surveys must typically rely on multiband photometry for determining the astrophysical properties (APs) of stars. Yet designing an optimal photometric system for a wide range of objects is complex, because it must trade off conflicting scientific requirements. I present a new method for designing photometric systems and apply it to the Gaia Galactic survey satellite, which will observe one billion stars brighter than V≈20. The principle is to optimally sample stellar spectra in order to determine the principal APs (Teff, [Fe/H], interstellar extinction etc.). By considering a filter system as a set of free parameters (central wavelengths, FWHM etc.), it may be designed by optimizing a figure-of-merit (FoM) with respect to these parameters. The FoM is a measure of how well the filter system can vectorially `separate' stars in the data space to avoid AP degeneracies. The resulting systems show some interesting features, in particular broad, overlapping filters, which may be desirable from a multivariate classification perspective. These systems are competitive with others proposed for Gaia.
http://www.mpia.de/homes/calj/

Variability and rotation of ultra cool dwarfs: a review

Coryn A.L. Bailer-Jones (Max-Planck-Institut fuer Astronomie Heidelberg)
Over the past few years monitoring programmes have shown ultra cool dwarfs (UCDs) to be photometrically variable. Of the ≈100 sources monitored, around a third show variability. For young (<100 Myr) cluster members (mid to late M dwarfs), this variability is generally periodic with amplitudes up to a few tenths of a magnitude and periods of a few hours to several days. For older field dwarfs (late M, L and T types) this variability is often nonperiodic with smaller amplitudes (up to 0.1 mag in I) and timescales of order hours. The former may be attributed to the rotational modulation of magnetically-induced photospheric spots, as seen in the higher mass T Tauri stars. The nonperiodic variability, on the other hand, may be caused by a rapid evolution of surface features (which `mask' the otherwise observable rotational modulation). This could be related to the formation and dissipation of inhomogeneities in dust clouds in the photospheres of UCDs. I will review the literature on UCD (spectro)photometric variability with the goal of casting light on the underlying mechanism(s) and look at its relation to UCD atmospheres and rotation.
http://www.mpia.de/homes/calj/

Stellar coronal abundances at high activity levels: ER Vul and UX Ari

Bill Ball (Smithsonian Astrophysical Observatory)
Jeremy Drake (SAO)
Vinay Kashyap (SAO)

We present analyses of Chandra HETG (MEG) spectra of the coronae of the active binaries, ER Vul and UX Ari. We used the Markov-Chain Monte Carlo method to reconstruct DEMs and produce abundances. The elemental abundances for ER Vul agree remarkably well with previous ASCA abundances and those of UX Ari show a significant enhancement of high FIP element abundances over low ones i.e. there is evidence of an inverse FIP effect in UX Ari.
http://cxc.harvard.edu

New Water Opacity For Cool Stars

Bob Barber (University College London)
Jonathan Tennyson (University College London)

Bob Barber & Jonathan Tennyson, University College London
NEW WATER OPACITY FOR COOL STARS
Water is the third most common molecule in the universe and its spectrum is particularly rich. It is the principal source of opacity in M,L and T dwarfs where it may account for in excess of 60% of the absorption in the IR.
Only a very small portion of lines in the water spectrum are known experimentally and consequently all model atmospheres and much spectroscopic work depend on line lists that have been generated ab initio using quantum mechanical modelling
None of the earlier line lists has been accurate enough to allow accurate modelling of stellar atmospheres. In addition the new generation of IR telescopes will require a spectroscopically accurate line list.
We have produced a new line list which contains approx. 620 million transitions (more than twice the number in earlier lists). Moreover, the BT1 list sets new standards in accuracy as the calculations utilise superior physics.
The BT1 line list will shortly be published, but it is already finding application in spectroscopy and in the modelling of stellar opacities: [1] P. -F. Coheur et al, J. Chem. Phys. (submitted) [2] H. Jones et al (in prep.) [3] N. Dello Russo et al, Icarus 168, 2004

Metal-poor star abundances from the HERES project

Paul Barklem (Department of Astronomy and Space Physics, Uppsala University)
N. Christlieb (Hamburger Sternwarte, Universität Hamburg)
T.C. Beers (Department of Physics and Astronomy, Michigan State University)

As part of the Hamburg/ESO R-process Enhanced Star (HERES) survey, several hundred "snapshot'' spectra of very metal-poor stars ([Fe/H] < -2) have been obtained with VLT2-UVES, with the main goal of finding stars enhanced in the r-process elements through detection of strong Eu II lines. Though the spectra are of low quality for abundance analysis by modern standards (typically S/N≈30, R≈20000, wavelength coverage 3760-4980 Å), they contain a wealth of information and abundances may be derived for a significant number of elements with moderate accuracy (r.m.s. errors of order 0.25 dex). The large number of stars in the HERES survey allows us to investigate general trends and scatter in metal-poor star abundances in a previously unexplored statistical regime, which may provide insights into mixing and the diversity of supernovae at early epochs. We have developed an automated analysis code based on the Spectroscopy Made Easy (SME) code by Valenti & Piskunov (1996) and used the code to obtain abundances for 22 elements where detectable. The method and preliminary results are presented and discussed.
http://www.astro.uu.se/~barklem

Extrasolar Planets: Atmospheres, Spectra, and Evolution

Travis Barman (Wichita State University)
France Allard, Isabelle Baraffe, Gilles Chabrier (CRAL-ENS, Lyon)
Peter Hauschildt (Hamburger Sternwarte)

The prospects of obtaining direct images and spectroscopy of extrasolar giant planets (EGPs) are steadily improving as new observatories and instruments continue to be developed at a rapid pace. New transiting planets are also being discovered which provide robust tests for EGP evolution models. In this poster, models are presented for the atmospheres, spectra, and evolution of EGPs for a variety of orbital separations, parent-star spectral types, and planetary masses. A particular emphasis will be placed on the different opacity assumptions currently being explored for EGPs and the impact these assumptions may have on the atmospheric structure and emergent spectrum.

First Doppler Images of Zeta Andromedae

Janos Bartus (Astrophysikalisches Institut Potsdam)
Zs. Kovari (Konkoly Observatory, Budapest)
K. G. Strassmeier (Astrophysikalisches Institut Potsdam)

First Doppler images are presented for the giant component of the RS CVn-type binary zeta And from 1997/98. Polar spottedness with several high latitude features are restored with a temperature contrast of about 800K from all the three mapping lines available, while only weaker features are recovered at low latitudes. Photometric behaviour and the effect of ellipticity are briefly discussed.

Spectroscopically Discerning Unresolved X-ray Sources from Late Type B Stars

Ehud Behar (Technion Israel Institute of Technology)
Maurice Leutenegger (Columbia University)
Rami Doron (Weizmann Institute)

It will be shown how high-resolution, grating spectroscopy provides a powerful tool for solving the puzzle of X-rays from late type B stars. Late type B stars are not supposed to be X-ray sources; nevertheless they have been detected in X-rays. We will present spectroscopic methods with which to determine whether it is the B star emitting the X-rays, or an unresolved low-mass companion. X-ray spectroscopy is the only viable approach when multiwavelength imaging (see the work by Stelzer at this meeting) fails to resolve the source. We apply the method to previously unpublished XMM-Newton and Chandra guest observations of mu Lep, a chemically peculiar late type B star revealing interesting results.
http://physics.technion.ac.il/~astrogr/

Photospheric temperature measurements in young main sequence stars.

Katia Biazzo (Universita' di Catania Dipartimento di Fisica e Astronomia)
Antonio Frasca (INAF - Osservatorio Astrofisico di Catania)
Gregory W. Henry (Tennessee State University - Center of Excellence in Information Systems)

As part of our program to study stellar photospheric and chromospheric activity, we have examined several young solar type stars with activity levels intermediate between the Sun and the very active RS CVn stars. We have analysed contemporaneous spectroscopic observations obtained at Catania Observatory (Serra La Nave station, Mt. Etna) and photometric data in the Strömgren bands acquired with several automatic photometric telescopes (APTs) at Fairborn Observatory (Arizona, USA). Surface inhomogeneities have been detected from the rotational modulation of stellar brightness and also the modulation of several photospheric line-depth ratios (LDRs). The presence of chromospheric plage-like regions has been inferred from the rotational modulation of the H-alpha line equivalent width evaluated with the spectral synthesis method. The most relevant results are the strong correlation between the brightness and temperature curves derived from photometry and the LDRs, respectively, as well as the striking anti-correlation between brightness and H-alpha emission. This suggests a close spatial association of spots and plagues, as frequently observed for the largest sun-spot groups (Catalano et al. 1998) and for some very active RS CVn systems (Frasca et al. 1998). Moreover, a simple spot/plage model applied to the observed flux curves allows a rough reconstruction of photospheric features of young main sequence stars.
References:
- Catalano, S., Rodono', M., Cutispoto, G., et al. 2000, in NATO Sci. Ser. C: Math. and Phys. Sci. 544, Variable Stars as Essential Astrophysical Tools, ed. C. Ibanoglu (Kluwer Academic Publishers), 68
- Frasca, A., Marilli, E., & Catalano, S. 1998, A&A, 333,205
http://woac.ct.astro.it

Magnetohydrodynamic Mode Coupling in the Quiet-Sun Network

D. Shaun Bloomfield (Queen's University Belfast)
R. T. James McAteer (NASA Goddard Space Flight Center, Solar Physics Branch)
M. Mathioudakis (Queen's University Belfast)

High-cadence, multiwavelength optical observations were taken at the National Solar Observatory/Sacramento Peak. A total of fifteen network bright points (NBPs) have been studied at differing atmospheric heights, using images taken in narrow wavebands. Wavelet analysis was used to study wavepackets, and identify traveling magnetohydrodynamic waves. Wave speeds were estimated through temporal cross-correlation of signals, in selected frequency bands of wavelet power, in each wavelength. Seven mode-coupling cases were identified, one in each of seven of the NBPs. MHD mode coupling is a viable mechanism for transport of energy from the photosphere into the chromosphere, where subsequent deposition can contribute to atmospheric heating.

Metallicity of M-dwarfs

Xavier Bonfils (Observatoire de Grenoble Observatoire de Genève)
Xavier Delfosse (Observatoire de Grenoble)
Stephane Udry (Observatoire de Genève)

M-dwarfs are small, very-low-mass, cool and faint stars. They are nevertheless the most numerous stars in the Galaxy.The study of their fundamental characteristics, such as their metallicity, is of prime importance to better understand their structure, their evolution, to determine their age and to constrain very-low-mass star models.
From high resolution spectroscopy of ELODIE spectra of separated visual binary components composed of F-, G- or K-dwarf primaries plus M-star secondaries, we determined the metallicity ([Fe/H]) of a sample of dwarfs of spectral type M. This goal was achieved by measuring the metallicity of the primary components and assuming that the secondaries have the same metal content. We believe that our approach is more reliable and straightforward than previous attempts to measure M-dwarf metallicities which used atmospheric model fitting directly on the M-dwarf spectra.
We report in this poster 20 new M-dwarf metallicities, hence increasing the (yet poor) sample of known M-dwarf metallicities by a factor of two. This on-going study focuses on aspects such as the dependence of the mass-luminosity function on the metallicity or the abundance of M-dwarf planet host star(s).

Light curves of active star CF Oct from the Bamberg observatory Southern Sky Survey

Ana Petrova Borisova (Institute of Astronomy, Bulgarian Academy of Sciences)
John L. Innis ()
Denis W. Coates (Monash University, Australia)

We present long-term photometric study of the active K subgiant star CF Oct from 1964 to 1976. It is based on over 350 scanned photographic plates from Bamberg Observatory plate archive. We performed aperture photometry and transformation to standard B magnitude for target star and 9 field stars for each plate. The accuracy of each individual measurement of CF Oct magnitude is 0.05 mag. Observational data-set gives us good phase covered light curves for the period 1964-1969, partial light curves for 1970 and 1976, and few data points for 1971. Our data confirm the known 20 d rotational period for the star, show evolution of light curves from year to year and changes in the amplitude from ≈0.2 to ≈ 0.4 mag.

Binaries among ultra-cool dwarfs and brown dwarfs

Wolfgang Brandner (Max-Planck-Institut fuer Astronomie)
Hervé Bouy (MPE)
Eduardo Martin (IAC)

Observations of brown dwarfs are expected to provide important feedback on theories of atmospheres and inner structure of substellar objects. In addition, brown dwarf binary systems offer the unique opportunity to determine the mass of individual brown dwarfs, which is one of the fundamental astrophysical quantities. We summarize ongoing surveys for brown dwarf binaries, and present results of follow-up studies using HST and ground-based adaptive optics.
http://www.mpia.de/homes/brandner

Chandra X-Ray Spectra of Contact Binaries

Nancy S. Brickhouse (Smithsonian Astrophysical Observatory)
Andrea K. Dupree (Smithsonian Astrophysical Observatory)
Ronnie Hoogerwerf (Smithsonian Astrophysical Observatory)

We present Chandra LETG/HRC-S spectra of the bright eclipsing contact binary 44i Boo. Chandra began observing the target on 22 Sept 2003 for an exposure time of 188.524 ks. This observation continuously covers 5.12 epochs of the binary system. Analysis of phase-binned spectra is compared with previous results from HETG/ACIS-S, which showed Doppler line shifts as a function of orbital phase (Brickhouse et al., 2001, ApJ, 562, L75). We expect these new data to provide additional information on the size, location, and variability of the high latitude emission. We also compare results with LETG/HRC-S spectra of the complementary contact binary system VW Cep.

Attacking the X-ray emission properties of young stars with the Sword of Orion

Kevin Briggs (Paul Scherrer Institut 5232 Villigen-PSI Switzerland)
M. Guedel (1), M. Audard (2) ((1) PSI, Switzerland; (2) Columbia Astrophysics Lab., USA )
K. Smith (3); R. Mewe (4); A.J.F. den Boggende (4) ((3) Max-Planck-Institut fuer Radioastronomie, Germany; (4) SRON, Netherlands)

A young star grows within a complex environment, accreting from a circumstellar disk and driving jet outflows out through a surrounding envelope of dust and molecular gas. Fast rotation and a fully-convective structure further distance the emerging star from the familiar Sun. The impact of these circumstances upon a stellar magnetic dynamo, the structure of magnetic field on the star and in its immediate environment, and resultantly the amount, location and temperature of X-ray-emitting hot plasma within the system is an issue of intense current interest. We use XMM-Newton to examine the X-ray emission properties of young stars in the Sword of Orion, and their dependencies on fundamental stellar parameters and environmental features. We find evidence for, and investigate possible causes of, reduced X-ray emission from systems in which active accretion is taking place.
http://www.astro.phys.ethz.ch/staff/briggs/briggs_nf.html

XMM-Newton Observations of Pleiades-Age K Dwarfs

Alexander Brown (CASA, University of Colorado)
Fonda Day; Thomas Ayres (CASA, University of Colorado)
Carol Ambruster (Villanova University)

We present XMM-Newton observations of young, active K dwarfs that were designed to study how coronal structure changes as a function of stellar rotation rate. RGS and EPIC spectra are being obtained for a sample of essentially identical, nearby (within 50 pc), Pleiades-age K dwarfs. Our four targets (HD220140 2.76d, HD174429 0.95d, HD17925 6.6d, and HD82443 5.4d), plus stars previously observed, cover the rotation period range from 0.5 to 6.6 days,and thus sample both the saturated and linearly-dependent portions of the coronal rotation-activity relation. We present the spectra obtained so far and our initial results for the coronal temperature/emission measure distributions and elemental abundances, and investigate the coronal energy budget.

Study of convection of giant stars using interferometry

Jo Bruls (Kiepenheuer-Institut für Sonnenphysik, Freiburg)
Oskar v.d. Luehe, Johannes Sahlmann (Kiepenheuer-Institut für Sonnenphysik, Freiburg)
Hans Ludwig (Lund University)

As a precursor of actual interferometric observations with the AMBER instrument at the VLT we investigate the feasibility of detecting and interpreting signatures of small-scale structures, in particular granules, at the surface of nearby cool giant stars. Starting from a snapshot of a hydrodynamic simulation of a T=4300K, log g=2.0 star, approx. K6III, we construct an image of the stellar disk in the light of a clean near-infrared spectral line and subject that to the appropriate interferometric observing and data analysis procedures. We will show and discuss first synthetic observations of such star assuming an angular extent of 0.05 arcseconds, which means that individual granules have an angular extent comparable to the theoretical spatial resolution limit of the VLTI.
http://www.kis.uni-freiburg.de/~bruls

The search for Solar-Like Oscillations in Procyon with the WIRE Satellite

Hans Bruntt (Department of Physics & Astronomy, University of Aarhus, Denmark)
Derek L. Buzasi (US Airforce Academy, Colorado, USA)
Hans Kjeldsen (Department of Physics & Astronomy, University of Aarhus, Denmark)

Helioseismology has allowed astronomers to probe the physics in the interior of the sun for the past decades. Only in the recent five years have asteroseismology of other sun-like stars been possible due to the advent of very stable spectrographs. One of the most interesting targets for seismology is Procyon A which is hotter and more evolved than the sun. Oscillations were first reported from a spectroscopic campaign by Brown et al. (1991) and firmly established by Martic et al. (2004). We here present the analysis of two data sets of high precision photometric data from the WIRE satellite.

The Current Status of the SuperWASP Project

Damian Christian (Queen's University Belfast)
D. Pollacco (Queen's University Belfast)
and the SuperWASP Consortium ()

We present the current status of the SuperWASP project, a Wide Angle Search for Planets. SuperWASP consists of up to 8 individual cameras using ultra-wide field lenses backed by high-quality passively cooled CCDs. Each camera covers ≈7.8 x 7.8 sq degrees of sky, for nearly 500 sq degrees of sky coverage. SuperWASP I, located in LaPalma, is currently operational with 5 cameras and is conducting a photometric survey of a large numbers of stars in the magnitude range ≈8 to 13. The collaboration is developing a custom-built reduction pipeline and aims to achieve better than 1 percent photometric precision. The pipeline will also produce well sampled light curves for all the stars in each field which will be used to detect: planetary transits, optical transients, and track Near-Earth Objects. Status of current observations, and expected rates of extrasolar planetary detections will be presented. The consortium members, institutions, and further details can be found on the web site at: http://www.superwasp.org.
http://www.superwasp.org/

Chromospheric activity in Proxima Centauri

Carolina Cecilia Cincunegui (Instituto de Astronomia y Fisica del Espacio, Buenos Aires, Argentina)
Pablo J. D. Mauas (Instituto de Astronomia y Fisica del Espacio, Buenos Aires, Argentina)

We present Echelle spectra of the dM5.5e star Proxima Centauri, obtained with the 2.15 m telescope of the CASLEO Observatory located in the Argentinean Andes. Our spectra range from 3900 to 6700 Åat a spectral resolution of R≈ 26400 and are flux-calibrated.
We have observations from 1999, taken in 10 different observing runs. We find very strong variability, even between spectra taken on the same night. This fact allows us to estimate the frequency of occurrence of flares.
We study several activity indicators, including the Ca II and H_α lines, the Na I D doublet and the He I D₃ line.
http://www.iafe.uba.ar/cincunegui

Asteroseismology of Procyon: Preliminary Results from SARG at TNG

Riccardo U. Claudi (I.N.A.F. Padova Astronomical Observatory)
Alfio Bonanno (I.N.A.F. Catania Astrophysical Observatory)
Rita Ventura (I.N.A.F. Catania Astrophysical Observatory)

We present the high precision radial velocity measurement on the F5 IV Star alpha CMi obtained from the SARG spectrograph at TNG exploiting the iodine cell technique. The analyzed spectra, a subset of the 950 time series points spanning 6 nights of Procyon observation, show individual measurement error of 1.3 m/s (very close to the theoretical photon noise limit Brown et al, 1994,PASP,106,1285). An excess of power between 0.5 and 1.5 mHz, detected also by Martic et al. (2004 A&A 418, 295) is found, but additional structure in the periodogram show up around 2.0 mHz. The time series obtained of the equivalent width of temperature-sensitive lines is also analyzed.

Pursuing the determination of absolute masses for young stars. Spectroscopic orbits of low-mass PMS systems in southern star formation regions.

Elvira Covino (INAF-Osservatorio Astronomico di Capodimonte, Napoli, ITALY)
Eike Guenther (Thueringer Landessternwarte Tautenburg)
Massimiliano Esposito (Universita' di Salerno, ITALY)

We report preliminary results of a high-resolution spectroscopic survey, and long-term monitoring on low-mass Pre-Main Sequence (PMS) spectroscopic binaries (SBs) in nearby Star formation regions of the Southern Hemisphere, aiming to seek for young long-period spectroscopic systems and solve their orbits. The spectroscopic program is part of a long-term project, fruit of an extended international collaboration, pursuing the determination of dynamical masses for a wide sample of young low-mass stars by combining both spectroscopic and interferometric techniques, with the ultimate aim to provide new observational constraints to PMS theoretical models.

High temporal resolution spectroscopic observations of UV Cet type flare stars

Inés Crespo-Chacón (Universidad Complutense de Madrid)
David Montes (Universidad Complutense de Madrid)
María Jose Fernández-Figueroa (Universidad Complutense de Madrid)

We present the results of a high temporal resolution spectroscopic monitoring of different flare stars (UV Cet type). The observations were done using the IDS spectrograph at the 2.5 m Isaac Newton Telescope (INT) (La Palma). Intermediate resolution spectra, including the Balmer lines from Hβ to H₁₀ as well as the He i 4026 Å and the Ca ii H & K lines, were taken using the R1200B dispersion grating (reciprocal dispersion ≈ 0.48 Å/pixel). The great number of spectra taken each night with high temporal resolution (15-60 s) allows us to analyse the temporal evolution of the emission lines in order to identify flares. Other variations at different scales have been also studied. For the strongest flares, we study differences on the behaviour of the lines of interest, in both the emission and profile.
http://www.ucm.es/info/Astrof/users/icc/icc.html

Is there a Role for High-Resolution EUV Spectroscopy in Research on Cool Stars?

Raymond Cruddace (Naval Research Laboratory, Washington D.C.)
Michael Kowalski (Naval Research Laboratory)
Kent Wood (Naval Research Laboratory)

High-resolution EUV spectroscopy has matured to where an orbiting instrument is feasible. For example, using multilayer-coated, ion-etched gratings, we could now build an EUV spectrometer array (≈100-300A) having high effective area (10-50 cm2) and spectral resolving power (≈10000). We summarise results which led to the flight demonstration of a prototype instrument. However, in proposals to NASA for an orbiting mission the scientific case has not reached the stage of taking on a major astrophysical issue. Instead it has pursued important but largely unrelated problems raised by past EUV observations. How EUV astronomy might take on major issues deserves debate, and in regard to cool stars we suggest two possibilities: 1) What coronae are telling us about magnetic dynamos, and their role in stellar evolution. 2) How coronae determine the interplanetary environment, and so may influence the development of life. The technology of high-resolution EUV spectroscopy is progressing rapidly, and we argue that the cool star community might review its significance as a research tool.

Time-dependent Ionization in Solar and Stellar Magnetic Flux Tubes

Manfred Cuntz (Department of Physics, University of Texas at Arlington)
Wolfgang Rammacher (Institut fuer Theoretische Astrophysik, Univ. Heidelberg)
Peter Ulmschneider (Institut fuer Theoretische Astrophysik, Univ. Heidelberg)

We discuss the relevance of time-dependent ionization in solar / stellar magnetic flux tubes. We focus on detailed models of longitudinal tubes waves taking into account recent simulations of wave generation, propagation and dissipation available for the Sun and solar-type stars. In particular, we study tubes of different spreading as function of height representing tubes in environments of different magnetic filling factors. Time-dependent ionization is relevant in all models studied to date. The effects of time-dependent ionization are most pronounced in simulations of high-amplitude waves and in tubes of narrow spreading owing to the properties of the waves and the lack of dilution of the wave energy flux. This work is a further step toward future research that will also consider transverse and torsional waves, thus allowing a more thorough understanding of magnetic heating phenomena in solar and stellar chromospheres.
http://www.uta.edu/physics/cuntz.html

The SUMER Spectral Atlas of Solar Coronal Features

Werner Curdt (Max-Planck-Institut für Aeronomie)
Enrico Landi (Artep Inc., Naval Research Laboratory)
Uri Feldman (Hulburt Center for Space Research, Naval Research Laboratory)

A far-ultraviolet and extreme-ultraviolet (FUV, EUV) spectral atlas of the Solar Corona between 670 Å and 1609 Å in first order of diffraction has been derived from observations obtained with the SUMER (Solar Ultraviolet Measurements of Emitted Radiation) spectrograph on SOHO. The atlas contains off-disc spectra of the quiescent corona, the corona above a coronal hole, the active corona and the flaring corona. The physical parameters of the coronal plasma are very different from those in the lower solar atmosphere, so the coronal spectrum includes a number of emission lines, which are difficult to observe elsewhere. Most of the lines in the spectrum have been identified, some of them for the first time. A percentage of the weaker lines remains without identification. The present atlas represents the most comprehensive and accurate line list for the solar corona in the 670-1609 Å wavelength range. This atlas also provides an excellent reference for astrophysical applications.
http://www.linmpi.mpg.de

A Deep Chandra X-Ray Observation of the Very Young Cluster NGC 6530

Francesco Damiani (INAF/Osservatorio Astronomico di Palermo ITALY)
E.Flaccomio, L.Prisinzano, G.Micela, S.Sciortino (INAF/OINAF/Osservatorio Astronomico di Palermo)
F.R.Harnden Jr., S.S.Murray (Harvard-Smithsonian Center for Astrophysics)

We present results of an X-ray observation of the very young cluster NGC 6530, associated with the Lagoon Nebula. We estimate that 95% of the 884 X-ray sources detected are low-mass cluster members, most of which not found by previous (even H-alpha) surveys. While only 220 X-ray sources are identified with catalogued stars (down to V=17), many more (731) are identified with infrared sources from 2MASS. We present also new, deeper optical photometry, which allows us to find an optical counterpart to more than 750 X-ray sources. From pre-main-sequence evolutionary models, we estimate that cluster stars have ages in the range 0.5-1.5 Myrs, with an age gradient from northwest to south, suggesting sequential formation. A group of X-ray sources showing frequent flares may be associated with the youngest stars in the cluster, suggesting that X-ray flaring activity is especially intense in the youngest PMS phases of low-mass stars. From the combined use of all available X-ray/optical/IR data we attempt to select as complete a possible cluster population, and to study the statistics of different stellar subgroups.

Spectropolarimetry of the Classical T Tauri Star T Tau

Antoun Daou (Rice University)
Christopher M. Johns-Krull (Rice University)
Jeff A. Valenti (Space Telescope Science Institute)

High resolution (R≈60,000) circular spectropolarimetry of the classical T Tauri star T Tau is presented. The star was observed on November 21, 1997. Analyzing 15 photospheric absorption lines, the mean longitudinal magnetic field is found to be B_z = 6 ± 16 Gauss. The 3σ upper limit is therefore 48 G, in contrast to a previously reported field of 150 G. As a check on our observing techniques and methods, spectra of the sun obtained by observing the asteroid Vesta are analyzed in the same fashion. Here, we find B_z = 4 ± 3 G, lending confidence to our results. As a further check, results are also presented for the magnetic Ap star 53 Cam.

Estimating effective temperatures of Mira Variables by fitting phase resolved spectra.

Matthias Dehn (Hamburger Sternwarte)
Schweitzer, Andreas (Hamburger Sternwarte)

Using an automatic procedure we compared the observed spectra of the Mira Variables R Leo, R CVn, V CVn, S Car and RZ Car with synthetic spectra which were generated with the PHOENIX atmosphere package. The observations were done by Castelaz et al. and Lancon et al. over several years in order to cover several pulsation phases.
We calculated a model grid with T_eff = 2000 … 4500 and log(g) = -1.0 … 2.5. Furthermore we changed the abundances of carbon and oxygen to obtain a C/O-ratio of 0.4, 0.8, 1.2 and 0.48 (solar) in order to get better fits. The models assume LTE and consider the condensation of dust inside the atmosphere.
The fit parameters (correlation coefficient and chi-square sum) are most sensitive to variations of temperature and C/O, whereas variations of log(g) are too small to resolve. A clear correlation between phase and temperature cannot be seen. Therefore, the temperatures were accounted as mean values which agree to calculations from Alvarez et al. (1997) for R Leo and R CVn and Shinkawa (1973) for S Car.

Spectral diagnostics of stellar coronae

Giulio Del Zanna (DAMTP, University of Cambridge UK)
Past and current satellites have provided a wealth of XUV spectroscopic observations of stellar coronae and transition regions (TR). However, measurements of basic characteristics have been elusive. For example, TR densities of active stars have most probably been overestimated by about an order of magnitude due to an incorrect assumption of ionization equilibrium. Much of the results (emission measures, temperatures, chemical abundances) currently published also rely on the same assumption. I review previous and new atomic data that allow direct measurements of electron temperatures for 10 MK plasmas, and use Chandra data to show that for some active stars the electron temperatures are clearly at odds with temperatures derived from emission measure distributions. This indicates a possible breakdown of ionization equilibrium.
http://www.damtp.cam.ac.uk/user/astro/gd232/astro.html

VRI observations of Open Clusters obtained with the REM telescope

Elisa Distefano (INAF - Catania Astrophysical Observatory)
Cutispoto G. (INAF - Catania Astrophysical Observatory)
Covino S. et al. on behalf of the REM team (INAF - Brera Astronomical Observatory)

The Rapid Eye Mount (REM) Italian telescope, an instrument which has been conceived and designed to immediately point and observe the Gamma-Ray Bursts detected by satellites, started operations at ESO (La Silla, Chile) in June 2003. VRI observations of the galactic Open Clusters Trumpler 26, Trumpler 31 and Collinder 347 were carried out by the authors in August 2003 during the commissioning of the telescope. Membership to the clusters was photometrically investigated and a large number of low mass stars belonging to the clusters have been found. The present data constitute a starting point for a detailed study of stellar activity in such clusters.
http://woac.ct.astro.it

Modelling magnetic activity in late-type giants

Bertil F. Dorch (The Niels Bohr Institute)
Recent evidence from numerical magneto-hydrodynamical simulations suggest that late-type giant stars may habour magnetic fields. In a "star-in-a-box" simulation, a red supergiant with stellar parameters similar to that of Betelgeuse was found to display both linear kinematic and non-linear saturated dynamo action: the non-linear magnetic field saturates at a super-equipartition value corresponding to surface magnetic field of field strengths up to solar values. In the linear regime two different modes of dynamo action are found. It is speculated that magnetic activity of late-type giants lead to the heating of the outer atmospheres of these stars.
http://www.astro.ku.dk/~dorch

Non-linear dynamo action in late-type giant stars: Numerical MHD simulations

Bertil Dorch (The Niels Bohr Institute Juliena Maries Vej 30 DK-2100 København Ø)
Evidence is presented from numerical magneto-hydrodynamical simulations for the existence of magnetic activity in late-type giant stars. A red supergiant with stellar parameters similar to that of Betelgeuse (alpha Orionis) has been modeled as a "star-in-a-box" with the high-order "Pencil Code". Both linear kinematic and non-linear saturated dynamo action are found: The non-linear magnetic field saturates at a super-equipartition value (a factor two above equipartition yielding surface fields with strengths on the order of 500 Gauss), while in the linear regime two different modes of dynamo action are found. It is speculated that magnetic activity of late-type giants may influence dust and wind formation and possibly lead to the heating of the outer atmospheres of these stars.
http://www.astro.ku.dk/~dorch

Modeling of outflowing envelopes of massive evolved stars at arbitrary optical depths

Anton Dorodnitsyn (Space Research Institute)
Bisnovatyi-Kogan G.S. ()

The many observational characteristics of a star with an extended outflowing envelope depend on the physical conditions in the envelope, and can be determined only via self-consistent computations of the evolution of stars taking into account mass loss. Application of “photospheric” outer boundary conditions can lead to sufficient errors in the solution for the outflowing wind provided that the envelope is geometrically extended. For evolved supergiants with extended, rarified envelopes, it is important to correctly take into account layers with low optical depths. Addressing these goals we develop a method that describes a radiation-driven wind that is formed due to absorption of the radiation flux in continuum. It allows to obtain a continuous transition of the solution from regions with large optical depth to the regions of the wind where the optical depth is small. In order to treat self-consistently regions with small we adopt “zero” boundary conditions posed at infinity. The numerical solution of the two boundary value problem (supersonic part of a wind) is obtained using relaxation technique.

Trouble on the Shock Front: TW Hydrae, X-rays and Accretion

Jeremy Drake (Smithsonian Astrophysical Observatory)
The classical T Tauri star TW Hydrae has an X-ray spectrum quite unlike that of any other active star or T Tauri star so far observed at high spectral resolution. Density-sensitive O VII and Ne IX lines seen in both XMM-Newton and Chandra spectra indicate plasma densities of order 10¹³ cm^-3 when interpreted in terms of collisional excitation, while the dominant plasma temperature is a rather cool 3 × 10⁶K. It has been suggested in the recent literature that these characteristics are indicative of emission from an accretion shock rather than from a coronal plasma. The accretion shock model is not without problems. Simple models suggest that such a shock should occur in the photosphere from which copious X-rays should not escape. In this paper, I discuss the problem of the X-ray spectrum of TW Hya in the context of the accretion scenario and its implications for the mass accretion rate and other aspects of the system.

Evolution of Stellar Coronae

Andrea Dupree (Harvard-Smithsonian Center for Astrophysics)
Nancy Brickhouse (Harvard-Smithsonian Center for Astrophysics)

Two single cool stars, Beta Dra and Alpha TrA offer a contrast in the structure and evolution of their outer atmospheres. Alpha TrA is a hybrid object, from a class of cool luminous stars originally identified based on C IV emission accompanied by absorption features indicating a massive stellar wind and circumstellar material. The atmosphere of Beta Dra appears to be similar to the Sun with high temperature emission, and lacking a massive wind. Spectra of these stars obtained with RGS-XMM/Newton show high temperature emission T≈10⁷K in their steady (non-flaring) state. A 1-T fit to the spectra suggests that the corona of Beta Dra is slightly hotter than that of Alpha TrA. Abundances of O, Ne, and Fe are 'solar' in Beta Dra, but O and Ne are enhanced with respect to solar in Alpha TrA. The density sensitive ratio of O VII transitions suggests that Alpha TrA has a lower density than Beta Dra. These spectra demonstrate that slowly-rotating giants and supergiants can have coronae hotter than the Sun. These spectra also give the first evidence that coronal structure changes, becoming cooler and less dense as luminous stars evolve to the hybrid phase.

CNO, S, Zn and Cu abundances in planet-harbouring stars

Alexandra Ecuvillon (Instituto de Astrofisica de Canarias)
Garik - Israelian (Instituto de Astrofisica de Canarias)
Nuno C. - Santos (Centro de Astronomia e Astrofisica de Universidade de Lisboa)

Abundance ratios of CNO, S, Zn and Cu were analysed in a large number of stars with exoplanets and in a homogeneous comparison sample of stars without any known planet, using high resolution and high S/N spectra from various telescopes/spectrographs. Nitrogen abundances were derived by spectral synthesis of the near-UV NH band at 3360 A, observed at high resolution with the VLT/UVES, and by EW measurement of the near-IR NI line at 7468. Carbon and oxygen abundances were derived by the EW measurements of two CI optical lines, and of [O I] 6300 A line and the O I 7774 A triplet, respectively. Spectral syntheses of several optical lines were performed for S, Zn and Cu. We compare relative abundances of volatile elements CNO, S and Zn and of the refractory Cu in planet host and comparison sample stars. We discuss possible interpretations of our data in the framework of the formation and evolution of planetary systems and provide new information for clarifying the importance of differential accretion.

The invisible component of a binary in the Horologium association

Guenther Eike (Thueringer Landessternwarte Tautenburg, D 07778 Tautenburg Germany )
Eike Guenther (Thueringer Landessternwarte Tautenburg, D 07778 Tautenburg, Germany)
Elvira Covino (INAF-Osservatorio Astronomico di Capodimonte via Moiariello, 16 - I 80131 Napoli, Italy)

In the cause of a survey for young spectroscopic binaries we found a highly interesting long period binary with an eccentric orbit in the Horologium association. The object is an SB1-binary with no trace of a secondary component, despite the high signal to noise of our spectra. The curiosity of this objects is that the visible component has a mass of about 0.9 solar-masses, and the m sin i of the invisible component is about 1.0 solar-masses! Thus, the mass of the invisible component is higher than that of the visible star. What could this object be? From the absence of a substantial IR-excess a very young, embedded objects seems unlikely. The other possibility would be a white dwarf, or a neutron star. Given the age of the object of about 35 million years, the progenitor of such an object would have to be a star of more than 10 solar-masses, which implies that it would have exploded as a supernova.

Multiwavelength observations of giant mass loss and interaction in eclipsing symbiotic binaries

Brian Espey (Physics Department, Trinity College, University of Dublin, Ireland)
Cian Crowley (Physics Department, Trinity College, University of Dublin, Ireland)
Stephan McCandliss (Department of Physics & Astronomy, Johns Hopkins University, Baltimore, MD USA)

We report on multiwavelength observations of the eclipsing binaries EG And, BF Cyg, RW Hya and SY Mus which are members of a sample of eclipsing symbiotic binaries from a program to study giant mass loss in these systems. Observations of the stars were made away from outburst, and include data taken from both ground and space (IUE, HST, FUSE). Comparison of spectra taken during, and outside of, eclipse enables tomographic information to be obtained for both the absorbing material and also the emission line gas. The systems span different properties (spectral type, mass loss, abundance, and companion type) and results obtained will be placed in these contexts.
http://www.tcd.ie/Physics/People/Brian.Espey

NGC 2264: a Chandra View

Flaccomio Ettore (INAF - Osservatorio Astronomico di Palermo)
We present first results of the analysis of a Chandra ACIS-I observation of the star forming region NGC 2264. We detect 420 in the 17'x17' FOV. Because of the much higher X-ray luminosity of PMS stars respect to field objects, we expect the vast majority of detected sources to be associated with low mass and/or embedded young members of NGC 2264. This interpretation is supported by their optical/IR colors and magnitudes. From the the X-ray selected member sample, we estimate masses for 300 stars using published optical photometry and evolutionary tracks. The thus estimated IMF is believed to be representative of the optically visible part of NGC 2264 in the whole stellar mass range. However, uncertainties in the masses estimated through photometry might be substantial for a small fraction of embedded members. Moreover the X-ray data disclose an additional population of deeply embedded PMS stars, that is not yet accounted for in this IMF.

Theoretical basal flux limits for stars with low metallicity

Diaa Fawzy (Astronomy Dept., Faculty of Science Cairo University, Egypt)
Wolfgang Rammacher (Institut for Theoretical Astrophysics, Univ. Heidelberg - Germany)
Peter Ulmschneider (Institut for Theoretical Astrophysics, Univ. Heidelberg - Germany)

The minimum observed stellar MgII h+k & CaII H+K chromospheric fluxes form what is called the basal flux line. These fluxes are referred to be originated by a non-magnetic heating mechanisms, the dissipation of the acoustic waves is thus identified as a source of heating. Observationally, the basal flux line is the same for the stars which have high or low metallicity. The current work shows the first theoretical basal flux lines for stars of different metallicity based on self consistent time- dependent chromosheric models. These models are computed using the following three basic parameters; the effective temperature, gravity and the metallicity.

Star - accretion disk interface in classical T Tauri stars

Matilde Fernandez (Instituto de Astrofisica de Andalucia, CSIC, Spain )
Sandra Ayala (Instituto de Astronomia, UNAM, Mexico)
Katsuo Ogura (Kokugakuin University, Japan)

A recent visible and near-infrared monitoring campaign of pre-main sequence stars (Eiroa et al. 2002) has identified several classical T Tauri stars where the near-infrared photometric variability is not correlated with the visible light curve. Since the most common causes of visible variability in young stars (star spots, accretion onto the star, and extinction) will produce correlated variations, these observations suggest that an additional mechanism might be contributing to the near-infrared variability: maybe physical changes in the inner accretion disk or changes in the inner-disk accretion rate (see also Skrutskie et al. 1996; Carpenter et al. 2001). We speculate that these changes might be associated to matter leaving the inner parts of the disk and moving towards the star, and will generate a hot spot at the impact region on the stellar surface.
In order to investigate further in this direction we have coordinated an international campaign (Japan, Mexico and Spain) with the aim of monitoring continuously a sample of classical T Tauri stars. Here we will present the first results of our simultaneous infrared and visible observations.
http://www.iaa.csic.es/~matilde/

Coronal mass transfer in interbinary loops

João Miguel Ferreira (Universidade dos Azores & Centro de Astrofisica da Universidade do Porto)
Cesar Mendoza-Briceno (Centro de Astrofisica Teorica, Universidad de Los Andes)

We consider the transfer of coronal mass between the members of a RS CVn binary system along interconnecting rigid magnetic loops. We show that the asymmetry in the gravitational potential drives a flow from the star closer to fill its Roche lobe towards the other star. The loop base pressures, the flow velocity and the mass flux are a result of this asymmetry together with the heating rate along the loop, and are not externally imposed. We find that the base pressures and mass transfer rate increase and the Mach number decreases as the loop heating increases. If the heating is not uniformly distributed along the loop then the mass transfer rate either increases or it decreases, and even changes direction, depending on which star the heating is concentrated on. Our model predicts mass transfer rates in reasonable agreement with existing observational estimates, only if the loop footpoints occupy a significant fraction of the stellar surfaces. But the model fails to explain the presence of chromospheric material detected between the stars. The differential emission measure profile of the loop is calculated and it is found to be significantly higher near the secondary star.

First COUP results: rotational modulation of X-ray emission from young stars

Ettore Flaccomio (INAF - Osservatorio Astronomico di Palermo )
The COUP collaboration (Several)

We introduce one of the first novel results of the Chandra Orion Ultradeep Project (COUP): the detection of rotational modulation of X-ray emission from the Orion Nebula Cluster (ONC) young stars. This remarkable result is made possible by the exceptional length of the COUP exposure: 10 days of almost uninterrupted ACIS observation during a time span of 13 days. We apply the Lomb Periodogram method to the X-ray light curves; comparing the thus derived rotational periods with published optically determined periods, we find evidence that the two are related. We discuss the implications of our results for the understanding of the physical properties and spatial distribution of the X-ray emitting plasma on the surface of PMS stars, most of which show saturated activity levels.

Detection of alpha-enhanced cool stars in the solar neighborhood

Mariagrazia Franchini (INAF-Osservatorio Astronomico di Trieste Via G. B. Tiepolo, 11 I-34131 Trieste ITALY)
Morossi C., Di Marcantonio P. (INAF-Osservatorio Astronomico di Trieste)
Malagnini M. L.; Chavez, M., Rodriguez, L. (Dipartimento di Astronomia, Universita` di Trieste; INAOE)

Cool stars, in particular F, G, and K main sequence stars, have deserved particular attention, in the framework of galaxy evolution studies. In fact, because of their long lifetimes, they still present the original chemical composition of their birth places and give insight into the star formation episodes when they were born. Of particular relevance are the abundances and kinematical analyses of those stars characterized by the so-called alpha-enhancement phenomenon which gives insights into the role of SN I and SN II in the chemical enrichment of individual stellar populations.
We present the results of an analysis of almost 2000 cool stars in the solar neighborhood aimed at the detection of alpha-enhanced stars and at the investigation of their kinematical properties. The analysis is based on the comparison of their spectral indices in the Lick/IDS system with synthetic ones computed with solar scaled abundances and with alpha-element enhancement. We used selected combinations of indices to single out 137 alpha-enhanced candidate stars. The kinematical properties of these objects are presented and compared with those of a sample of 239 stars for with solar scaled abundances are very-likely.

The sigma Orionis open cluster observed with XMM-Newton: source detection and spectral properties

Elena Franciosini (INAF/Osservatorio Astronomico di Palermo Piazza del Parlamento 1, 90134 Palermo, Italy)
Roberto Pallavicini (INAF/Osservatorio Astronomico di Palermo, Palermo, Italy)
Jorge Sanz-Forcada (Astrophysics Division - Research and Science Support Dept. of ESA, Noordwijk, The Netherlands )

We present XMM-Newton observations of the young (≈2-5 Myr) cluster around the hot (O9.5V) star sigma Orionis AB. We have obtained both EPIC imaging data of the cluster and a high-resolution RGS spectrum of the hot star. We have detected 174 X-ray sources, of which 76 are identified as cluster members, including very low-mass stars down to the substellar limit, and discovered rotational modulation due to surface activity in a K-type star of the cluster. We have also detected a strong X-ray flare from the B2Vp star sigma Ori E, which we attribute to an unseen late-type companion. We present the results of the EPIC spatial and spectral analysis of the cluster sources, and compare them with those obtained for other young clusters. We also discuss the results of the high-resolution spectral analysis of the central hot star sigma Ori AB.

Newly discovered active binaries in the RasTyc sample of X-ray stellar sources

Antonio Frasca (INAF - Osservatorio Astrofisico di Catania, via S. Sofia 78, I--95123 Catania, ITALY)
Patrick Guillout (Observatoire Astronomique de Strasbourg, 11 rue de l'Université, 67000 Strasbourg, FRANCE)
Ettore Marilli (INAF - Osservatorio Astrofisico di Catania, via S. Sofia 78, I--95123 Catania, ITALY)

The cross-correlation between the ROSAT all-sky survey (150,000 sources) and the Tycho mission (1,000,000 stars) catalogues has selected about 14,000 stellar X-ray sources (RasTyc sample, Guillout et al. 1999).
About 300 stars have been spectroscopically observed at high resolution both in H-alpha and LiI-6708 regions with Elodie and Aurelie spectrographs of the OHP (Observatoire de l'Haute Provence, France) with the aim of classify the stars of the RasTyc sample in the northern hemisphere in terms of age, rotation rate and chromospheric activity level and to detect eventual binary systems.
In this work we present preliminary results of follow-up observations, both photometric and spectroscopic, of a RasTyc sub-sample performed with the 91-cm telescope of the Catania Astrophysical Observatory, Italy.
In particular, we have discovered and studied a few late-type binaries, obtaining good radial velocity curves and solving for the orbits. Filled-in or emission H-alpha profiles have been observed. We have also detected, in some cases, a photometric modulation ascribable to photospheric surface inhomogeneities and chromospheric H-alpha line variation.
References
- Guillout, P., Schmitt, J. H. M. M., Egret, D., Voges, W., Motch, C., & Sterzik, M. F. 1999, A&A 351, 1003
http://woac.ct.astro.it

Synthetic line profiles from numerical simulations of a red supergiant

Bernd Freytag (GRAAL, Université de Montpellier II)
Michelle Mizuno-Wiedner (Astronomical Observatory, Uppsala University)
Bengt Gustafsson (Astronomical Observatory, Uppsala University)

Radiation hydrodynamic simulations of the outer envelope and the atmosphere of a red supergiant (like Betelgeuse) have been performed with CO5BOLD. The equation of state accounts for ionization processes and the non-local radiative energy transport uses detailed (grey) opacities.
The resulting models reveal a variety of surface features that can be attributed to small surface and large envelope convection cells, to pressure fluctuations in the stellar interior and shock waves in the atmosphere.
We will demonstrate the imprint of these processes on synthetic line profiles computed from the numerical models.
http://www.astro.uu.se/~bf/

Modeling M-dwarf chromospheres with PHOENIX

Birgit Fuhrmeister (Hamburger Sternwarte Gojenbergsweg 112 21029 Hamburg)
J. H.M.M. Schmitt (Hamburger Sternwarte)
P. Hauschildt (Hamburger Sternwarte)

We construct semi-empirical model chromospheres with the atmospheric code PHOENIX. The model atmospheres consist of a photosphere in thermal equilibrium and an arbitrary temperature rise in the chromosphere and part of the transition region. The photosphere chosen is our best fit to the photosphere of AD-Leo, of which we have high-resolution UVES spectra in the wavelength range of 3000 to 6700 Å. We use these spectra for modeling the temperature rise as a function of the column mass. Specifically we investigate the influence of NLTE for the most important species, the influence of the temperature gradient and the influence of the temperature minimum. We present first model spectra and compare them to the averaged spectrum of AD Leo.
http://www.hs.uni-hamburg.de/DE/Ins/Per/Fuhrmeister/index.html

Close Binarity in CTTSs

Gösta F. Gahm (Stockholm Observatory AlbaNova SE - 106 91 Stockholm, Sweden)
Peter Petrov (Crimean Astrophysical Observatory, Ukraine)
Eric Stempels (Nordic Optical Telescope, La Palma, Spain)

Our spectroscopic monitoring, using VLT and NOT, of several classical T Tauri stars (CTTSs) reveals one new suspected close binary, namely the bright and well-known star RU Lupi. For this star we find low-amplitude velocity variations on a time-scale of a few days, consistent also with literature values obtained at other periods of time. Velocity changes were also found in RY Lupi, but in this case we can show that these are related to distortions in the shape of photospheric absorption lines caused by stellar spots passing over the stellar surface. For RY Tauri, on occasions reported to host a hidden companion, we find a constant radial velocity within ± 1 km s^-1 over periods of up to 13 days. For other program stars we also derive constant velocities.
We demonstrate how data like these can be used to find restrictions on mass and distance of possible hidden companions. We also combine our measurements with data from the literature and update the growing list of confirmed and suspected close binaries in the CTTSs group.

Oxygen abundances in young open clusters

Ramon J. Garcia Lopez (Instituto de Astrofisica de Canarias, La Laguna, Tenerife, Spain)
Sofia Randich (Osservatorio di Arcetri, Firenze, Italy)
Artemio Herrero (Instituto de Astrofisica de Canarias, La Laguna, Tenerife, Spain)

Oxygen abundances have been derived in two young open clusters (≈50 Myr) from the IR O I triplet at 7771-7774 A, using high resolution, high S/N UVES VLT spectra. Additional simultaneous measurements of UV OH bands and the [O I] line at 6300 A were performed in the same stars. These measurements will allow us to investigate lithium depletion patterns in the two clusters, and to cross-calibrate oxygen abundances derived from the three different indicators in stars with solar metallicity and a range of effective temperatures. Comparison with abundances derived consistently from available data in a wide sample of Galactic open clusters with ages up to ≈6 Gyr and different Galactocentric distances will provide key insights in the recent Galactic evolution of oxygen.

Systematic errors in determinations of stellar rotational velocities

Robert Glebocki (Intitute of Theoretical Physics and Astrophysics, University of Gdansk)
Piotr Gnacinski (Intitute of Theoretical Physics and Astrophysics, University of Gdansk)

Measurements of Vsini are based on the analysis of rotational broadening of spectral lines. The most frequently used methods of analysis are the following: cross-correlation technique, full width at half maximum, convolution and Fourier transform of line profile (FTLP). Except for the last one, results depend critically on the adopted templates and standards used for calibration of line broadening as a function of Vsini. Using our updated and corrected catalogue of Vsini determinations (more than 27000 data for about 17000 stars) we have found systematic differences in the published values of Vsini. E.g. the CORAVEL values are systematically higher than that from FTLP method; in some cases data presented in a given publication differ by up to 15% from the other measurements. In conclusion we suggest introduction of commonly accepted standards for Vsini calibration. Additionally, we discuss level of accidental errors typical for each method of Vsini evaluation.

High resolution spectroscopy of recently discovered chromospherically active binary stars

M. Cruz G'alvez (Universidad Complutense de Madrid)
David Montes (universidad complutense de madrid)
Maria Jose Fernandez-Figueroa (universidad complutense de madrid)

During last years (1999-2004) we have carried out a spectroscopic survey of young single late-type active stars possible members of young stellar kinematic groups, in order to study the kinematic and spectroscopic properties of these groups of stars. One of the results of this survey is the detection of a set of active stars showing noticeable radial velocity variations. Multiwavelength optical observations have allowed us to determine precise radial velocities by cross correlation with radial velocity standard and then to confirm or dismiss the binarity. In addition, we have obtained information about orbital solution and about the activity of the chromosphere of these active binary systems using the information provided for several optical spectroscopic features (from the Ca ii H & K to Ca ii IRT lines) that are formed at different heights in the chromosphere.
The chromospheric contribution in these lines has been determined using the spectral subtraction technique.
Rotational velocities (vsini) and lithium (Li i λ6707.8) equivalent widths were determined too.
http://www.ucm.es/info/Astrof/users/mcz/mcz.html

CLOUDS IR spectroscopic time-series of brown dwarfs

Bertrand Goldman (MPIA)
CLOUDS collaboration ()

Time resolved spectral observations of brown dwarfs offer the opportunity to constrain and characterize atmospheric variability. Since there have been several reports of brown dwarf photometric and spectroscopic variability and since one mechanism accounting for the L/T dwarf transition is compatible with variability, we obtained spectroscopic time series for five L6 to T6 brown dwarfs in the SZ band using Isaac on VLT-Antu and in JHK bands using SpeX on IRTF. High spectral-frequency variations are seen in some objects, but these detections are marginal and require confirmation. We find no evidence for large amplitude variations in spectral morphology and we place firm broad band variability upper-limits, of 1 to 4%, depending on targets and wavelengths, on the time scale of a few hours. Assuming that any variability arises from the rotation of large scale holes in an otherwise global cloud deck across the surface, we find that the typical physical scale of cloud cover disruption should be smaller than ≈10% of the disk size, assuming simplistic heterogeneous atmospheric models.
http://astronomy.nmsu.edu/bgoldman/

Near-Infrared Photometry and Spectroscopy of L and T Dwarfs: the Effects of Clouds, Gravity, and Effective Temperature

David A. Golimowski (Department of Physics and Astronomy Johns Hopkins University)
Sandy K. Leggett (Joint Astronomy Centre)
Mark S. Marley (NASA Ames Research Center)

We present new JHKL'M' photometry on the MKO system for a large sample of L and T dwarfs identified from SDSS and 2MASS and classified according to the scheme of Geballe et al. We have now compiled a sample of over 100 L and T dwarfs that are uniformly classified and measured on a single photometric system. The scattered JHK spectral indices and colors of L dwarfs are likely caused by variations in the altitudes, distributions, and thicknesses of condensate clouds. Scatter in the H-K colors of late T dwarfs probably reflects the sensitivity of the K-band flux to pressure induced H2 opacity, which itself is sensitive to surface gravity. The M' luminosities of late-T dwarfs are 1.5-2.5 times fainter than predicted under conditions of chemical equilibrium. We have computed L_bol and T_eff of 42 L and T dwarfs for which trigonometric parallaxes have been measured. We find that T_eff ≈ 1450 K for types L7-T4, which supports recent models that attribute the changing JHK-band luminosities and spectral features across the L-T transition to rapid changes in the condensate clouds over a narrow range of T_eff. We compute T_eff = 600-750 K for 2MASS 0415-0935 (T9), which supplants GJ 570D as the coolest known brown dwarf.
http://acs.pha.jhu.edu/~dag

The spectroscopic diagnosis of warm MHD winds

Ana I Gomez de Castro (Instituto de Astronomia y Geodesia (CSI-UCM), Fac. CC Matematicas, Univ. Complutense de Madrid)
C. Ferro-Fontan (CONICET)
E. Verdugo (ISO Data Center - VILSPA)

Self-similar models for warm MHD disk winds have been analyzed following Sakurai (1985) and Vlahakis et al (2000) formulations. The winds are assumed to depart from keplerian rings of warm gas (T = 10⁵ K) which could be formed in the corona of accretion disk or in the stellar magnetosphere-inner accretion disk interaction region where magnetic energy is dissipated and heats the gas. The models provide a detailed solution for the bipolar flow, e.g., thermal, density and velocity laws, which has been used to determine the emissivity of the most relevant forbidden lines. It is shown that the emissivity in the inner 10 AUs is dominated by the ultraviolet semiforbidden lines of CIII](190.8nm) and SiIII](189.2nm). Detailed predictions on the line profiles and the lines ratios are presented and compared with the observations obtained with HST/STIS. It is shown that the main signature of the winds is generating broad wings, with FWHM around few 100 km/s on the profiles of these lines which adds to the chromosphere/transition region contribution.
http://www.mat.ucm.es/~aig

X-ray spectroscopy of the FK Comae type star V1794 Cygni

Philippe Gondoin (European Space Agency - ESTEC)
V 1794 Cygni, a chromospherically active late-type giant with a high X-ray luminosity, was observed by the XMM-Newton space observatory.Series of lines of highly ionized Fe and several Lyman lines of hydrogen-like ions are visible in the reflection grating spectra, most notably from O and Ne. Analysis results suggest a scenario where the corona of V1794 Cygni is dominated by large magnetic structures similar in size to interconnecting loops between solar active regions but significantly hotter. The surface area coverage of these active regions may approach up to a 90 %. An hypothesis is that the interaction of these structures themselves induces a flaring activity in a small scale not visible in the EPIC light curves that is responsible for heating V1794 Cygni plasma to coronal temperatures of T > 10⁷ K. The intense X-ray activity of V 1794 Cygni is related to its evolutionary position at the bottom of the red giant branch. It is anticipated that its rotation will spin-down in the future with the effect of decreasing its helicity related, dynamo driven activity and suppressing large scale magnetic structures in its corona.
http://www.rssd.esa.int/

X-ray spectroscopy of the Hertzsprung gap giant HD 223460

Philippe Gondoin (European Space Agency - ESTEC)
HD 223460 (HR 9024), a chromospherically active late-type giant with a high X-ray luminosity, was observed by the XMM-Newton space observatory. Series of lines of highly ionized Fe and several Lyman lines of hydrogen-like ions and triplet lines of helium-like ions are visible in the reflection grating spectra, most notably from O and Ne. Analysis results suggest a scenario where the corona of HD 223460 is dominated by large magnetic structures similar in size to interconnecting loops between solar active regions but significantly hotter. The surface area coverage of these active regions may approach up to a 30 %. An hypothesis is that the interaction of these structures themselves induces a flaring activity in a small scale not visible in the EPIC light curves that is responsible for heating HD 223460 plasma to coronal temperatures of T > 10⁷ K. The intense X-ray activity of HD 223460 is related to its evolutionary position at the bottom of the red giant branch. It is anticipated that its rotation will spin-down in the future with the effect of decreasing its helicity related, dynamo driven activity and suppressing large scale magnetic structures in its corona.

Stochastic Methods for the Calculation of Mean Values of the Specific Intensities in Moving Late Type Atmospheres

Christian A. Graf (Institute of Theoretical Astrophysics)
Rainer Wehrse (Institute of Theoretical Astrophysics)

Cool stars show an extremely large number of atomic and molecular lines in their spectra. Unfortunately, in addition to the lines that are visible in spectra there are many more weak lines present that cannot be observed directly. They form a quasi-continuum. The question arises how these lines should be included in models. Since an individual treatment of all lines is very time-consuming, for static media several methods have been developed that result in specific intensities or fluxes that are averaged over a certain wavelength interval, e.g. methods involving opacity distribution functions or the opacity sampling method. Recently, Baschek et al. have proposed ways to generalize the opacity distribution functions to moving cases and to calculate them directly from a given line list or by means of a Poisson point process. After an introduction to these methods we present first results for the generalized opacity distribution function based on presently used line lists (assuming solar composition). We will discuss in particular its variation with the velocity gradient and demonstrate the changes in the effective absorption coefficient (that replaces the Rosseland mean absorption coefficient for static media) due to motions. Finally, we will address the problem of incomplete line lists and their consequences.

Some critical remarks on quasi-static stellar evolution models.

Thomas Granzer (Astrophysikalisches Institut Potsdam (AIP) An der Sternwarte 16 D-14482 Potsdam)
Strassmeier, K.G. (AIP)

Quasi-static stellar evolution has been tackled numerically as early as electronic data-processing entered the field of astronomical research some fifty years ago. Despite some improvements in the description of turbulence, opacities, or in the equation of state, the results presented by different authors still show a rather wide spread in results. This poster tries to provide some hints on the reasons of these discrepancies and tries to point at difficulties that may arise from using theoretical stellar evolutionary tracks for mass/age determination of observed stars.

Doppler imaging of UX Arietis on Nov.-Dec. 2001

Sheng-hong Gu (National Astronomical Observatories/Yunnan Observatory, Chinese Academy of Sciences)
Hui-song Tan (National Astronomical Observatories/Yunnan Observatory)
Hong-guang Shan (National Astronomical Observatories/Yunnan Observatory)

The high-resolution observation for RS CVn star UX Ari was carried out using echelle spectrograph of the 2.16m telescope at Xinglong station on Nov.-Dec. 2001. Two usual spectral lines FeI6430.844A and CaI6439.075A are analyzed by using Doppler imaging technique, and the starspot pattern of UX Ari is obtained. Compared with the previous results derived by Aarum et al. (1999) and us (2003), the starspot feature and evolution of UX Ari are discussed.

Coronal X-rays from jet-driving embedded young stars?

Manuel Guedel (Paul Scherrer Institut CH-5232 Villigen PSI Switzerland)
Alessandra Telleschi and Kevin R. Briggs; Stephen L. Skinner (PSI; University of Colorado)
Marc Audard; Kester W. Smith; Kaspar Arzner (Columbia Univ.; MPIfR Bonn; PSI)

We report on Chandra X-ray observations of jet/outflow-driving young stars in the Taurus and Orion star forming regions. We have selected sources with strong optical and radio jets (or outflows) that are highly inclined against the line of sight in order to optimize the probability of detecting X-rays that originate from the inner jets. The stars themselves are located behind thick molecular/dust disks that are seen nearly edge-on. We report X-ray detections of several of these systems. The strongly absorbed X-ray sources are detected in the harder bands, and their location very close to the position of the young stars suggests that we are observing some type of coronal emission from these objects.
http://www.astro.phys.ethz.ch/staff/guedel/guedel_nf.html

The Eclipsing Binary CM Dra: A Study with XMM-Newton

Manuel Guedel (Paul Scherrer Institut CH-5232 Villigen PSI Switzerland)
Alessandra Telleschi; Stephen L. Skinner (PSI; Univ. of Colorado, Boulder)
Marc Audard; Jan-Uwe Ness & Juergen Schmitt (Columbia University; Hamburger Sternwarte)

We present recent XMM-Newton X-ray observations of the eclipsing M dwarf binary CM Draconis (dM4.5, P = 1.27 d, i = 89.8 deg), obtained with XMM-Newton around each of the two optical eclipses. The X-ray light curves reveal clear and long (1-2 hours) eclipses of coronal material, additional to some intrinsic X-ray variability. We present a light curve analysis, the emission measure distribution obtained from spectroscopy, and an analysis of coronal abundances. The principal results will be compared with the earlier-type (dM1e), more active eclipsing binary, YY Gem.
http://www.astro.phys.ethz.ch/staff/guedel/guedel_nf.html

An invisible component of a binary in the Horologium association

Eike Guenther (Thueringer Landessternwarte Tautenburg, D 07778 Tautenburg, Germany)
Eike Guenther (Thueringer Landessternwarte Tautenburg)
Elvira Covino (INAFOsservatorio Astronomico di Capodimonte)

In the cause of a survey for young spectroscopic binaries we found a highly interesting long period binary with an eccentric orbit in the Horologium association. The object is an SB1-binary with no trace of a secondary component, despite the high signal to noise of our spectra. The curiosity of this objects is that the visible component has a mass of about 0.9 solar-masses, and the m sin i of the invisible component is about 1.0 solar-masses! Thus, the mass of the invisible component is higher than that of the visible star. What could this object be? From the absence of a substantial IR-excess a very young, embedded objects seems unlikely. The other possibility would be a white dwarf, or a neutron star. Given the age of the object of about 35 million years, the progenitor of such an object would have to be a star of more than 10 solar-masses, which implies that it would have exploded as a supernova.
http://www.tls-tautenburg.de/

Very Low Mass X-ray flaring star 1RXS J115928.5-524717

Valeri Hambaryan (Astrophysikalisches Institut Potsdam)
Axel Schwope (Astrophysikalisches Institut Potsdam)
Eike Guenther (Thueringer Landessternwarte Tautenburg )

A new very low mass star in the solar neighborhood, originally was identified as a most probable optical counterpart of a flaring X-ray source detected in the ROSAT All-Sky survey. Optical spectroscopy and infrared photometry consistently reveal a spectral type of M9 ± 0.5 and a distance of 11 ± 2pc. The optical counterpart of 1RXS J115928.5-524717 shows a large proper motion of 1.08±0.06 arcsec/year. A huge X-ray flare, reached an unprecedent value of L_X/L_bol ≈ 0.1 among VLM stars. VLT+UVES high resolution spectroscopy showed an absence of Li and confirmed VLM nature of a fast rotating (vsini ≈ 25 to 26 km/s) star.

A Metatheory About Spicules

Reiner Hammer (Kiepenheuer-Institut für Sonnenphysik Freiburg, Germany)
Anastasios Nesis (Kiepenheuer-Institut für Sonnenphysik, Freiburg, Germany)

Spicules dominate the solar coronal mass balance. Their driving mechanisms have not yet been identified, although numerous theories have been put forward that appear to be able to explain the most basic spicule properties, i.e. their velocities and heights. We point out, however, that some observational facts, in particular the spicular group behavior and bipolar flows, are inconsistent with a unique driving mechanism. Thus it may well be that different driving mechanisms are operating at different times and places on the Sun, depending on the dynamics and magnetic topology. The basic reason why all these mechanisms produce spicules with the same observed speed must be sought in the equipartition between kinetic energy density and specific enthalpy, and also with the magnetic energy density in the case of magnetic mechanisms. We show that equipartition between enthalpy and kinetic energy is a natural consequence of all mechanisms that are based on a strong pressure gradient in the upper chromosphere, which results from either a pressure increase in the lower, or a decrease in the upper atmosphere.

H3+ in cool, very metal poor stars.

Gregory John Harris (Department of Physics and Astronomy, University College London)
S. Miller and J. Tennyson (Department of Physics and Astronomy,University College London)
A. E. Lynas-Gray (Department of Physics, University of Oxford)

In a cool hydrogen-helium gas, the molecular ion H3+ is known to be an important electron donor and as such has an important effect upon the continuous opacity of the gas. This extra opacity can affect both the structure and evolution of hydrogen-helium stars of less than half a solar mass. In stars of solar metallicity, H3+ is largely destroyed by the electrons released from the metals. However as metallicity is reduced toward the hydrogen-helium limit, H3+ becomes increasingly abundant and hence important. Here we discuss the range of metallicities over which H3+ is the dominant positive ion. Furthermore we discuss the possibility of detecting rotation-vibration lines of H3+ in very metal poor stars, such as the most iron poor star known, HE0107-5240 ([Fe/H]=-5.3).
http://www.tampa.phys.ucl.ac.uk/~greg/

Improving the quality of HCN/HNC and H¹³CN/HN¹³C data.

Gregory John Harris (Department of Physics and Astronomy, University College London, Gower Street, London, UK)
J. Tennyson (Department of Physics and Astronomy,University College London)
H. R. A. Jones And Ya. V. Pavlenko ()

The HCN/HNC linelist of Harris et al. (2002) ApJ, 578, 657, is the most accurate and extensive ab initio linelist in existence. It has been used to identify HNC in a carbon star for the first time (Harris et al. 2003, MNRAS, 344, 1107). However, it suffers from the inherent accuracy problems of ab initio data. The band centres of some overtone bands deviate by up to 10 cm^-1 from experimental values. This give rise to problems when attempting to identify individual lines and bands within medium to high resolution spectra of cool carbon rich stars. To improve the quality of many of our line frequencies we have substituted the available experimentally determined HCN energy levels for their ab initio counterparts, thus improving the accuracy of many of the strongest HCN/HNC line frequencies. We are currently repeating this process for H¹³CN and HN¹³C in order to create a H¹³CN / HN¹³C linelist.
http://www.tampa.phys.ucl.ac.uk/~greg/

First Results from the Thueringer Landessternwarte Tautenburg Planet Search Program

Artie Hatzes (Thueringer Landessternwarte Tautenburg)
Eike Guenther (Thueringer Landessternwarte Tautenburg)
Ana Bedalov (Astrophysical Institute and University Observatory Jena)

The Thueringer Landessternwarte Tautenburg (TLS) Planet Search Program was started in January 2001. It uses precise stellar radial velocity (RV) measurements taken with an iodine absorption cell to search for extrasolar planets among a diverse class of stars. This program has detected two giant planets candidates. One is in a nearly circular orbit in the habitable zone around a G-type star: period = 375 d (a = 1.04 AU), e = 0.056, M sin i = 9.9 Jupiter masses. The second extrasolar planet has a minimum mass of 4.9 M Jupiter and a semi-major axis = 1.2 AU (Period = 418 d) in orbit around what we believe to be a K giant star. This star also shows considerable short-term RV scatter typical for stars of this class. Our program has also discovered a rare (co-discovered by the McDonald Planet Search Program) brown dwarf companion in an eccentric orbit around the star HD 137510. The orbital parameters are: M sin i = 26 Jupiter masses, P = 798 d, e = 0.4. Radial velocity surveys have established that brown dwarf companions to stars are much rarer than extrasolar giant planets.

Cool Stars in the Gaia photometric system

Ulrike Heiter (Department of Astronomy and Space Physics, Uppsala University)
Nikolai Piskunov, Bengt Gustafsson (Department of Astronomy and Space Physics, Uppsala University)
Carme Jordi, Josep M. Carrasco (Departament d'Astronomia i Meteorologia, University of Barcelona)

The Gaia space astrometry mission, currently under development at ESA, will in addition to the astrometric measurements obtain photometry for all detected sources. Two sets of filters, placed in the focal planes of the astrometric and spectroscopic telescopes, will enable the classification of the measured stars in terms of effective temperature, surface gravity and metallicity. Using photometric data simulated for different possible filter sets and spectral energy distributions calculated from stellar atmosphere models, we employ principle component analysis to investigate the suitability of these filter systems for determining the astrophysical parameters of late-type giants and dwarfs.
http://www.astro.uu.se/~ulrike

Beta Pictoris, far-UV emission lines, and a boundary layer

Marc Hempel (AIU Jena)
Jan-Uwe Ness (Hamburger Sternwarte)
Jürgen H.M.M. Schmitt (Hamburger Sternwarte)

Beta Pictoris is the most prominent prototype of stars with circumstellar disks and has generated particular interest in the framework of young planetary systems.Concerning its spectral type A5, stellar activity is unexpected. Nevertheless, resonance lines of C III and O VI have been unambiguously detected with FUSE, implying the possible existence of a chromosphere.We present XMM observations of Beta Pic and find no evidence for X-ray emission suggesting the absence of stellar activity. These findings present a challenge for the development of both stellar activity and disk models. We demonstrate that an accretion disc - boundary layer model is capable of explaining the observational properties of Beta Pictoris.
http://www.astro.uni-jena.de/Contact/members.html

The STELLA I telescope: a status report after finishing the test phase at Hamburg.

Alexander Hempelmann (Universität Hamburg Hamburger Sternwarte)
Jose Nicolas Gonzalez Perez (Hamburger Sternwarte)
STELLA team (Hamburger Sternwarte and Astrophysikalisches Institut Potsdam)

STELLA I is an automatically operating telescope with an 1.2m aperture equipped with a fiber-coupled Echelle-spectrograph with resolving power R = 50000. STELLA I is a joint project between the University of Hamburg and the Astrophysical Institute Potsdam, in collaboration with the IAC (Spain). The Hamburg contribution to this project is the telescope. It was delivered to Hamburg in 2002 and tested there until May 2004. This status report shall demonstrate the optical performance as well as pointing, tracking and guiding accuracies as finally observed during the test phase.
http://www.hs.uni-hamburg.de/DE/Ins/Per/Hempelmann/index.html

Analysis of high temporal resolution spectra of late-type rapid rotator stars

Maria Magdalena Hernan-Obispo (Universidad Complutense de Madrid)
Elisa de Castro,Inés Crespo-Chacón (Universidad Complutense de Madrid)
M.C. Galvez (Universidad Complutense de Madrid)

In this contribution we present the results of high temporal resolution spectroscopic observations of a sample of active stars. High resolution echelle spectra have been obtained in February 2004 using SOFIN spectrograph at 2.56m Nordic Optical Telescope (NOT, La Palma) and in April 2004 at FOCES spectrograph in 2.2m Telescope in Calar Alto Observatory. We selected the sample according to the following common properties: high level of chromospheric activity, late spectral types(K or later), young evolutionary stages, high rotation rates ((vsini)> 50 km/s). In each run continuous series of spectra were taken during visibility time of the star. The analysis of these spectra allow us to monitoring the temporal evolution of the Hα line profile. From the equivalent width and radial velocity variation with rotational phase of the star it's possible to detect the presence of prominence-like clouds (dense and cool material embedded in the hotter stellar corona). In addition, the simultaneous analysis of the different optical chromospheric activity indicators (Hβ (4861Å), He I D₃(5876Å)) allow us to discriminate what kind of structure we are detecting in Hα.

Interferometric observations of the Mira star o Ceti with the VLTI/VINCI instrument in the near-infrared

Karl-Heinz Hofmann (Max-Planck Institute for Radio Astronomy)
H.C. Woodruff (Max-Planck Institute for Radio Astronomy)
D. Schertl (Max-Planck Institute for Radio Astronomy)

We present K-band commissioning observations of the Mira star prototype o Cet obtained at the ESO Very Large Telescope Interferometer (VLTI) with the VINCI instrument and two siderostats. The observations were carried out between 2001 October and December, in 2002 January and December, and in 2003 January. Rosseland angular radii are derived from the measured visibilities by fitting theoretical visibility functions obtained from center-to-limb intensity variations (CLVs) of Mira star models. Using the derived Rosseland angular radii and the SEDs reconstructed from available photometric and spectrophotometric data, we find effective temperatures ranging from T_eff = 3192 +/- 200 K at phase φ = 0.13 to 2918 +/- 183 K at φ = 0.26. Comparison of these Rosseland radii, effective temperatures, and the shape of the observed visibility functions with model predictions suggests that o Cet is a fundamental mode pulsator. Furthermore, we investigated the variation of visibility function and diameter with phase. The Rosseland angular diameter of o Cet increased from 28.9 +/- 0.3 mas (corresponding to a Rosseland radius of 332 +/- 38 R_sun for a distance of D = 107 +/- 12 pc) at φ = 0.13 to 34.9 +/- 0.4 mas (402 +/- 46 R_sun) at φ = 0.4. The error of the Rosseland linear radius almost entirely results from the error of the parallax, since the error of the angular diameter is only approximately 1 %.

Rotational evolution of stars with latitude-dependent magnetised winds

Volkmar Holzwarth (School of Physics & Astronomy University of St Andrews)
Moira Jardine (School of Physics & Astronomy, University of St Andrews)

Spectro-polarimetric observations of rapidly rotating active stars have revealed the presence of complicated surface and coronal magnetic field structures. Frequently, however, only a single - allegedly characteristic - field strength is used to determine the stellar angular momentum loss owing to a magnetised wind. Here, I examine the dependence of the rotational evolution of a star on different latitude-dependent magnetic field distributions, analytically prescribed close to the stellar surface. For each latitude the angular momentum loss is determined according to the classical Weber-Davis approach, assuming an axial symmetric and polytropic stationary wind. The variations of the parametrised field distributions and thermal wind properties with rotation rate are assumed to follow simple power laws. The results show that the latitudinal dependence of magnetised winds can cause considerable deviations of the rotational evolution from previous simplified approaches.

De-Carbonated Cool Dwarfs in Cataclysmic Variables

Derek Homeier (Department of Physics and Astronomy The University of Georgia)
Thomas E. Harrison (New Mexico State University)
Steve B. Howell (WIYN Observatory and NOAO)

Secondary stars of cataclysmic variables exhibit a variety of abundance anomalies, possibly caused by deposition of CNO-processed material from the primary during the common-envelope phase. IR-spectroscopy of the ultra-short-period CVs U Geminorum, and EF Eridani, one of the strongest candidates for a substellar companion, show evidence for significant carbon underabundance. We have calculated PHOENIX models for late-type stellar and substellar atmospheres using chemical equilibrium compositions for a variety of elemental abundances including carbon/oxygen depletion and nitrogen enrichment. Comparisons of these models with medium-resolution K-band spectra of U Gem confirm a [C/Fe] ratio at least 1 dex below the solar value. We also show that the IR spectrum of EF Eri requires a T_eff in the brown dwarf range, and the virtual absence of CH₄ and/or CO absorption features in this object indicates a similar depletion of carbon. Time resolved H- and K-band spectroscopy however reveals a much more complex emission from this system, and we conclude that cyclotron emission contributes substantially to the IR spectrum even in the low state. Additional underabundance of oxygen, enrichment of nitrogen, and/or a possibly much lower temperature of the secondary, contributing only a fraction of flux to the observed spectrum, may have to be taken into account for a full understanding of this CV.
http://phoenix.physast.uga.edu/~derek/

Spectral Analysis of Ultracool Dwarfs

Derek Homeier (Department of Physics and Astronomy The University of Georgia)
Peter H. Hauschildt (Hamburger Sternwarte)
France Allard (CRAL-ENS, Lyon)

Improvements in stellar atmosphere models over the past years have allowed us to reproduce most of the fundamental spectral properties of very-low-mass stars and brown dwarfs. Yet ultracool stellar atmospheres still defy quantitative spectral analysis using classical techniques such as individual line profile fitting. The reasons for this are the absence of a true continuum in a SED deviating strongly from a blackbody, and large uncertainties in the input data to the opacity calculation: atomic and molecular line strengths and dust microphysics. Similar uncertainties exist for the chemical composition of atmospheres subject to convective mixing and overshoot. As a result, theoretical uncertainties almost always dominate observational errors, in particular with new, high S/N data, prohibiting a straightforward application of established techniques like χ²-minimisation. I will present estimates of the impact of these uncertainties on derived parameters by comparing results from different input data and physical models. I comment on the prospect of deriving reliable values for surface gravity or abundances by spectral analysis, which would allow studying these parameters independently of evolutionary models.
http://phoenix.physast.uga.edu/~derek/

Constraining coronal structure using X-ray spectra: a Chandra study of AB Dor

Gaitee A.J. Hussain (ESTEC/ESA)
Nancy S. Brickhouse (Harvard Smithsonian CfA)
Andrea K. Dupree (Harvard Smithsonian CfA)

The Chandra X-ray observatory monitored the single star, AB Dor, continuously for a period lasting 88ksec (1.98 Prot) in 2002 December with the LETG/HRC-S. The exposure is divided into eight quarter-phase bins and the centroids of the strongest emission line profiles measured. Doppler shifts in the strongest line profile, O VIII 18.97 A, are found to repeat in consecutive cycles. In velocity-space, this cyclic modulation has a semi-amplitude of 30km/s. This pattern of modulation indicates that a significant component of AB Dor's X-ray emitting corona is concentrated in a compact high latitude region. The X-ray lightcurve shows 12% rotational modulation, with three significant peaks that repeat in successive cycles.These peaks may indicate the presence of three compact emitting regions in the quiescent corona; one or more of these regions is likely to be causing the measured O VIII Doppler shifts. We conclude that this region is located near 60 degrees latitude, close to AB Dor's surface and discuss how this might relate to AB Dor's surface magnetic activity distribution.

Studying Evolution in Maunder Minimum Stars With a New Survey of Chromospheric Ca II Emission

Wright Jason (University of California, Berkeley)
Geoffrey Marcy (University of California, Berkeley)

We present chromospheric CaII activity measurements, rotation periods and ages for ≈1200 F, G, K, and M main-sequence stars from ≈18,000 archival spectra taken at Keck and Lick Observatories as a part of the California and Carnegie Planet Search Project. We have calibrated our chromospheric S-values against the Mt. Wilson chromospheric activity data.
From these measurements we have calculated activity levels and derived R'HK, stellar ages, and rotation periods. We also present precise time series of activity measurements for these stars.
We also show that many stars previously identified as Maunder minimum stars are actually slightly evolved off the main sequence. We have used our activity measurements and Hipparcos parallaxes to demonstrate that the relation often used to derive ages of main sequence stars breaks down as a star evolves off the main sequence. We find that stars only 1 magnitude above the main sequence exhibit significantly suppressed activity levels which have been mistaken for examples of Maunder minimum behavior.
http://astro.berkeley.edu/~jtwright

Alfv'en Wave Driven Winds in Cool Supergiant Stars

Vera Jatenco-Pereira (Instituto de Astronomia, Geofísica e Ciências Atmosféricas - IAG/USP)
Aline de Almeida Vidotto (IAG/USP)

There are in the literature several theories to explain the mass loss in stellar winds. In particular, for late-type stars, the most promising acceleration mechanism for driving these winds involves the mass loss by an outward-directed flux of damped Alfvén waves. For most of these models, these winds are taken as isothermal, with constant damping length and with radial magnetic field. In the present work, we present a model of Alfvén wave driven winds using the resonant surface damping mechanism and a diverging geometry for the magnetic field as we know from observational data from coronal holes in the Sun. The mass, momentum and energy equations are solved in a self-consistent approach. We obtain the velocity and the temperature profiles of the wind compatible with observations of a K5 supergiant star.

First Direct Evidence for a Polar Cap on SV Cam

Sandra Jeffers (School of Physics & Astronomy, University of St Andrews)
Andrew Collier Cameron, John Barnes (University of St Andrews)
Jason Aufdenburg / Gaitee Hussain (National Optical Astronomy Observatory / ESTEC)

We have used spectrophotometric data from the Hubble Space Telescope to eclipse-map the primary component of the RS CVn binary SV Cam over 9 HST orbits. We find from these observations and the HIPPARCOS parallax that the surface flux in the eclipsed low-latitude region of the primary is about 30% lower than computed from a PHOENIX model atmosphere at the effective temperature that best fits the spectral energy distribution of the eclipsed flux. This can only be accounted for if about a third of the primary's surface is covered with unresolved dark star-spots. Extending this to the full surface of the primary, we find that even taking into account this spot filling factor there is an additional flux deficit on the primary star. This can only be explained if there is a large polar spot on the primary star extending from the pole to latitude 48 +- 6 degrees.

Modeling of stellar chromospheres: phoenix vs. multi

Darko Jevremovic (Dept. Physics and Astronomy, University of Oklahoma, 440 W. Brooks NH 131, Norman 73019, US )
E. Baron (University of Oklahoma)
P. Hauschildt (Hamburger Sternwarte)

We present a detailed comparison of NLTE chromospheric modeling of late type stars using two radiative transfer codes phoenix and multi. For comparison purposes we built a grid of fifty schematic models with T_eff=3300K, logg=5 and different positions of the temperature minimum and transition region representing different levels of activity.
We compare our results using different setups of each code and especially the influence of the EOS, background opacities (atomic and molecular), atomic data, and the number of species treated in NLTE. The differences are in some cases significant and they highlight the importance of understanding results among different groups. This work gives us an important link with previous modeling and future introduction of more 'physical' assumptions in phoenix.

Towards characterization of exoplanetary spectra with the VLT Interferometer

Viki Joergens (Sterrewacht Leiden / Leiden Observatory)
Andreas Quirrenbach (Sterrewacht Leiden / Leiden Observatory)

Differential phase observations with a near-IR interferometer offer a way to obtain spectra of extrasolar planets. The method makes use of the wavelength dependence of the interferometer phase of the planet/star system, which depends both on the brightness ratio between the planet and the star and on the interferometer geometry. The differential phase is strongly affected by instrumental and atmospheric dispersion effects. Difficulties in calibrating these effects might prevent the application of the differential phase method to systems with a very high contrast as required for planet detection. A promising alternative is the use of differential closure phases, which are immune to many of the systematic and random errors affecting the single-baseline phases. We have modeled the response of the AMBER instrument at the VLTI to realistic models of known extrasolar planetary systems taking into account their (theoretically calculated) spectra as well as the geometry of the VLTI. We will discuss the instrumental requirements, calibration procedures and observing strategies that may lead to a successful characterization of exoplanetary atmospheres in the near-IR.

A New Parallax Measurement to the Pleiades Star Cluster

Christopher M. Johns-Krull (Rice University)
Jay Anderson (Rice University)

We report on a new program to determine the distance to the Pleiades Open cluster by means of measuring its trigonometric parallax. Digital Sky Survey images from 1951 November are used with widefield I band imaging obtained at McDonald Observatory in 2002 February to determine the proper motion of the cluster and to identify low mass cluster stars. Using this membership list, 3 fields were identified in which multiple cluster stars fit onto a single Hubble Space Telescope ACS/WFC image. HST-ACS observations of these fields were obtained in 2003 July and 2004 January through the F475W and F814W filters. Combined with our previous proper motion measurement for the cluster, the HST-ACS data is used to measure the parallax of 10 low mass cluster stars. We will present our data and parallax determination which we expect to be accurate to ∼ 5%.

PoSSO - Physics of SubStellar Objects

Hugh Jones (University of Hertfordshire)
PoSSO collaboration ()

A full understanding of the properties of substellar objects is one of the major challenges facing astrophysics. Since their discovery in 1995, hundreds of brown dwarfs and extrasolar planets have been discovered. While these discoveries have enabled important comparisons with theory, observational progress has been much more rapid than the theoretical understanding of cool atmospheres. The determination of mass, abundances, gravities and temperatures is not yet possible. The key problem is that substellar objects emit their observable radiation in the infrared region of the spectrum where our knowledge of atomic, molecular and line broadening data is poor. In order to understand these objects, and extra-solar planets increasing more like those our Solar System, we urge the wider physical chemistry community to engage in this exciting new field. Here we sketch an outline of the atoms, molecules and processes requiring study
http://www.astro.livjm.ac.uk/~hraj

Convection, atmospheres and winds of red supergiant stars

Eric Josselin (GRAAL - University Montpellier II)
Bertrand Plez (GRAAL - University Montpellier II)
Bernd Freytag (GRAAL - University Montpellier II)

Red supergiant stars (RSG) constitute a key-phase in the evolution of massive stars, characterized by strong mass loss with unknown origin. On-going radiative hydrodynamics (RHD) simulations of these stars with CO5BOLD show a peculiar convection pattern, with giant cells.
We present high-resolution, multi-epoch spectroscopy of a sample of RSG, which provides a diagnostic of their atmospheric dynamics. We compare them with synthetic spectra based on 3D RHD models. We investigate the role of the convective motions for the generation of the observed mass-loss rates.

Analysis of CaII emission lines in late type stars

Clarissa Kaiser (University of Hamburg, Hamburger Sternwarte)
Marc Hempel (University of Hamburg, Hamburger Sternwarte)
Jürgen H.M.M. Schmitt (University of Hamburg, Hamburger Sternwarte)

We have computed spectra with a grid of NLTE-Models from 5000 K to 8000 K and from logg=3.0 to 5.0 with the atmospheric code PHOENIX. The photospheric models have no chromosphere or corona. To identify chromospheric activity we compared the modelled spectra with the data from the stars of our sample. An indicator of chromospheric activity which can be used for slow rotating stars is the well-known (Mt.Wilson) S-Index which is defined as the ratio between the emission in the CaII line cores at 3933.66 and 3968.47 Angstrom and the continuum. We developed a new method to measure the chromospheric activity by comparing the residual equivalent width of the CaII lines between model and data. The advantage of this method is that it also works for fast rotating stars up to vsini=160 km/s. Here we present our new method and the first results of our comparative studies with the S-Index.

Solar and Stellar Chromospheres

Wolfgang Kalkofen (Harvard-Smithsonian Center for Astrophysics)
The sun is a prototype for late-type stars. Its chromosphere plays a role as a boundary region for the acceleration of the solar wind. It is therefore important to know whether the upper layers of the solar chromosphere, and hence of stellar chromospheres, experience the violent temperature fluctuations (δ T > 10⁴ K) and strong shocks obtained from hydrodynamical simulations based on an observed photospheric velocity field, or whether the chromosphere is as quiescent as SUMER observations of emission lines would suggest (δ T ∼ 10² K-10³ K). This paper examines the validity of the dynamical model and concludes that its main value is as a tool for probing the physics of the chromosphere, but that the actual chromosphere of the sun is a relatively quiescent medium.

How typical is the Sun among other stars with the cyclic activity?

Maria Katsova (Sternberg State Astronomical Institute Moscow State University)
Moissei A.Livshits (Institute of Terrestrial Magnetism, Ionosphere and Radio Wave Propagation)

New data on the X-ray and chromospheric emission of late- type stars allow us to re-compare physical processes on the Sun and other stars with well-pronounced cycles. We show that the "X-ray Sun" locates on the same arrow as other slow-rotating G and K stars with cycles, but its corona is noticeably weaker, while a level of the solar chromospheric activity is close to the mean ones for these stars. Causes of such a distinction between the Sun and other stars with cycles are discussed. As compared with these stars, the Sun is the hotter and posses smaller filling factor. On the Sun near to the minimum of the cycle, the heating of the corona in closed loops is proportional to the magnetic field strength therein, while the coronal heating in regions with open magnetic field lines at poles and in coronal holes is diminished when the magnetic field increases. On other stars with cycles the heating in closed magnetic fields can be more effective. The Sun becomes brighter in optics as its chromospheric emission increases. On other stars this correlation is expressed weaker and then transforms into anticorrelation for stars with the high, irregular activity.

The angular size of dwarf stars and subgiants - Surface brightness relations calibrated by interferometry

Pierre Kervella (Observatoire de Paris-Meudon)
Frederic Thevenin (Observatoire de la Côte d'Azur)
Damien Ségransan (Observatoire de Genève)

The availability of a number of new interferometric measurements of Main Sequence and subgiant stars allowed us to calibrate the surface brightness (SB) relations of these stars using exclusively direct angular diameter measurements. These empirical laws allow to predict stellar angular diameters based on broadband photometry. The smallest intrinsic dispersions (< 1% on the angular size) are obtained for the relations based on visible (B or V) to infrared (K or L) color indices. Our calibrations are valid between the spectral types A0 and M2 for dwarf stars, and between A0 and K0 for subgiants. Such relations are particularly useful to estimate the angular size of calibrators for long baseline interferometry. The corresponding visible-infrared SB relations derived from interferometric measurements of Cepheids lead to almost identical SB relations. From this strikingly good agreement between stars of vastly different physical natures, we propose that the visible-IR SB relations (based on the V-K index for instance) are valid for a very broad range of stars.

How Anti-Solar Rotation Laws can be produced

Leonid Kitchatinov (Inst. Solar-Terrestrial Physics, Irkutsk)
Guenther Ruediger (Astrophysical Institute Potsdam)

There are observational claims of detecting anti-solar differential rotation laws with the stellar equator rotating slower than the poles. We thus discuss the theoretical possibilities for the origin of equatorial deceleration. The standard hydrodynamical models for global circulation in convection zones do always produce solar-like differential rotation with equatorial acceleration. We argue that the antisolar rotation can be produced though if the meridional flow is amplified by any additional driver which is not included in the standard formulation. Both magnetic polar spots or tidal forcing from a close companion are possible amplifiers of the meridional circulation. Theoretical estimations and first results of numerical simulations for polar spots as the reason for the equatorial deceleration are reported. Observers should be motivated to find the peculiarities of the stars with anti-solar rotation laws.

The Effects of Partial Redistribution on the Calculated O I Lines of the Late-type Stars alpha Tau and beta Gem

Rachel Koncewicz (Department of Theoretical Physics, University of Oxford)
The spectra of late-type stars show a large number of fluorescent lines, which can be used to investigate chromospheric inhomogeneities. I will present calculations of the intensities of the fluorescent O I lines, which are pumped by the Hydrogen Lyman beta line, for the stars alpha Tau (K5 III) and beta Gem (K0 III). These calculations have been performed using the atmospheric models of McMurry (1999) and Sim (2002), with the radiative transfer code of Uitenbroek (2001). They include a full Partial Redistribution (PRD) treatment both of the H Lyman lines, which has been shown to have a significant effect on the line profile (Sim, 2001) and the O I lines.

OP And - an evolved giant with evidences for activity and mass-loss.

Renada Konstantinova-Antova (Institute of Astronomy, Bulgarian Academy of Sciences)
K.-P.Schröder, M.M. Ivanov, A.P.Antov, D.Z.Kolev ()

A detailed spectral and photometric study of the apparently single K giant OP And is presented. The behavior of H_α and of the photospheric temperature sensitive line CaI 6572.8A in the period 1993 - 2000 are studied together. H_α appears filled-in to a significant degree with a blue-shifted emission feature. A strong variability is found with both lines. The photometric behavior of the star confirmed the 76d period reported earlier. We also detected flares on this star. The spectral and photometric behavior of OP And is interpreted in terms of magnetic activity and existence of close and open magnetic loops in the atmosphere of this giant. The analysis of its evolutionary stage and chemical abundances revealed that it is a star of 1.6 M_sun evolved beyond the base of the RGB. Its position in the HRD with resect to the different dividing lines is also discussed.

FK Com - A Flip-Flop Dynamo?

Heidi Korhonen (Astrophysikalisches Institut Potsdam An der Sternwarte 16 D-14482 Potsdam)
Detlef Elstner (Astrophysikalisches Institut Potsdam)

In many active stars the spots concentrate on two permanent active longitudes which are 180 degrees apart. In some of these stars the dominant part of the spot activity changes the longitude every few years. This, so-called flip-flop phenomenon, was first discovered in a single, late type giant, FK Com. Since then the phenomenon has been reported in 6 other stars, both single and binaries alike and including also the Sun. To explain this phenomenon non-axisymmetric dynamo mode, giving rise to two permanent active longitudes at opposite stellar hemispheres, is needed together with an oscillating magnetic field. In this poster we present a dynamo solution, where both solutions exist together giving the appearance of the flip-flop phenomenon. The model uses a solar type rotation law with about 10% of the solar differential rotation and an anisotropic alpha. The flip-flop persists in a regime, where the drift of the non-axisymmetric mode is twice the oscillation period of the axisymmetric alphaOmega-dynamo, similar to a swing excitation. Under reasonable assumptions for the magnetic diffusivity, periods of several years can be found.

Surface differential rotation on FK Com

Heidi Korhonen (Astrophysikalisches Institut Potsdam, Germany)
Svetlana V. Berdyugina (ETH-Zentrum, Zurich, Switzerland)
Ilkka Tuominen (Institute of Astronomy, Oulu University, Finland)

In this work 24 surface temperature maps of the single, late-type, giant, FK Com for the years 1993--2003 are presented. They are analysed together with the long-term photometry spanning 40 years to investigate the spot properties and evolution on the surface of FK Com and determine the value of the surface differential rotation. All the three methods used in this study yield a surface differential rotation where the equator is rotating faster than the poles (solar type differential rotation) and which is in strength approximately 10% of the solar value.

Spectral studies of K dwarfs

Eira Kotoneva (Tuorla Observatory/ York University)
Gang Zhao (National Astronomical Observatories of China)
Jianrong Shi (National Astronomical Observatories of China)

K dwarfs are long lived, low mass stars, which offer us an unique opportunity to study the evolution of the Solar neighbourhood and the whole Galaxy in more detail than earlier when the studies were concentrated on F and G dwarfs.
We have obtained a relatively high resolution spectra with signal to noise ratio 80 < S/N < 280 for 52 nearby K dwarfs. The absolute magnitude limit for the stars is between 5.5 < MV < 7.3 and the initial metallicities are between -1.52 < [Fe/H] < 0.48. The data was taken in the Xinglong station with 2.16m telescope in China during 2003 and 2004.
We have defined the physical parameters, i.e. effective temperatures, surface gravities and microturbulent velocities for the sample and further determined the LTE abundances for 16 elements. We confirm the discrepancy in the abundances derived from the neutral and the ionized lines and believe that some serious modifications should be done to the present models of the stellar atmospheres of K dwarfs.

Differential rotation of LQ Hya and IL Hya from time-series Doppler images

Zsolt Kovari (Konkoly Observatory)
Michael Weber (AIP)
Klaus G. Strassmeier (AIP)

A technique of detecting differential rotation from time-series Doppler images is introduced and applied to LQ Hya and IL Hya. For the rapidly rotating K2 dwarf LQ Hya we find an almost rigid rotation, with weak (alpha=0.0056) equatorial acceleration. A bit stronger solar-type differential rotation was detected on the giant component of the RS CVn-type IL Hya with alpha=0.03.

The character of accretion and stellar wind parameters of T Tauri stars.

Alexandra Kravtsova (Sternberg Astronomical Institute, Moscow)
Lamzin S.A. (Sternberg Astronomical Institute, Moscow)

Quantitative parameters of disk wind were derived from the analysis of optical and UV spectra of CTTS. We found the matter outflows from a disk region with an outer radius of < 0.5 AU. The outflowing matter initially moves almost along the disk until being accelerated up to V> 100 km/s and only afterwards begins to collimate. Inner region of the wind is collimated into the jet at a distance <3 AU. from the disk mid plain. The V_z gas velocity component in the jet decreases with increasing distance from the jet axis. The gas temperature in the jet bottom is less then 20.000 K.
We found that the main portion of emission continuum of CTTS is formed outside the accretion shock, what means a great deal of accretion matter falls onto the star in nearly horizontal direction. This gas decelerate in turbulent layer near the star surface. We suggest two scenarios to explain such nature of accretion: two-stream accretion (through boundary layer and magnetosphere) and magnetospheric accretion by way of streams, the bulk of matter in which falls onto the star in nearly horizontal direction.

Differential rotation of late-type stars

Manfred Kueker (Astrophysikalisches Institut Potsdam)
Guenther Ruediger (Astrophysikalisches Institut Potsdam)

Differential rotation has been observed for a number of low-mass main sequence and pre-main sequence stars. We present a model for the rotation of these stars based on the mean field theory of angular momentum transport and the results of simulations of rotating convection.
We present the results of Box simulations confirming the anisotropy of the heat transport in rotating stratified convection zones and study its impact on the stellar rotation. The horizontal temperature gradient caused by the anisotropy is small, but sufficient to counteract the rotational shear as a driving force of meridional flow, thus reducing the efficiency of the latter in smoothing out any non-cylindrical rotation pattern. This allows a solar-type differential rotation to exist for Taylor numbers as large as 10⁷, which is impossible with isotropic heat transport.
We study the dependence of the surface differential rotation on spectral type and rotation rate. The dependence on the rotation rate turns out to be weak, with the maximum shear at rotation periods close to the convective turnover time.

Long-term starspot evolution, active longitudes and activity cycle of V 711 Tauri (HR 1099)

Antonino Francesco LANZA (INAF - Osservatorio Astrofisico di Catania)
M. Rodonò (Dept. of Physics and Astronomy University of Catania)
S. Messina, N. Piluso, G. Cutispoto (INAF - Osservatorio Astrofisico di Catania)

We present the first results of the analysis of a sequence of optical light curves of the magnetically active close binary V711 Tau (HR 1099). Our data base consists of 26 seasonal light curves spanning the 1976-2001 interval and it was obtained by complementing the already published photometry with unpublished APT photometry. Maximum Entropy and Tikhonov regularized spot models are derived by means of the approach proposed by Lanza et al. (1998, A&A 332,541) and allow us to study the distribution and the evolution of the active longitudes on the cooler K1 IV component as well as its activity cycle.

CHIANTI - an atomic database for X-EUV emission lines

Enrico Landi (Naval Research Laboratory)
CHIANTI is a database of atomic data and transition probabilities for the analysis of optically thin spectra at all wavelength ranges. In the present work I will describe the new version of CHIANTI, which includes a large number of new data to predict the X-ray spectrum of hot coronae in the Sun and stars. The new version of CHIANTI is ideal for the analysis of high resolution X-ray spectra from Chandra and XMM.

Observations and models of solar active region loops

Enrico Landi (Naval Research Laboratory)
Massimo Landini (Universita' di Firenze, Italy)

In the present work we compare CDS, SUMER, EIT and Yohkoh observations of several quiescent active region loops in the Sun to a steady-state, dynamic loop model developed adopting several different heating mechanisms, commonly used in the literature. We find that no one of the adopted heating mechanism reproduces the observations. We also find that loop temperature profiles and chromospheric/transition region lines are better reproduced if the loop cross-section is assumed to be non-uniform, with very small values at the loop footpoints.

Long-lived disk accretion in nearby pre-main sequence populations

Warrick Lawson (University of New South Wales/ADFA, Canberra ACT 2600, Australia)
Many of the nearest young stellar populations such as eta Cha, eps Cha and the TW Hya association share a kinematic origin with the nearest OB association (Oph-Sco-Cen) and have inferred ages of 5-12 million years. These stars are prime targets for all early stellar and planetary evolution issues, including the issue of circumstellar disk longevity. Optical/IR study finds a small fraction of these stars still possess inner disks and are undergoing disk accretion at 8-10 Myr, a timescale comparable to that demanded by core accretion to grow Jovian planets to near their final masses.

On the tidal synchronization in late-type binary systems

Izan C. Leao (Departamento de Fisica - UFRN)
Jose R. De Medeiros (Departamento de Fisica - UFRN)

The evolution of tidal synchronization in late-type binary systems is analyzed from a comparison between observational data and theoretical predictions. The behavior of V/V_k, where V and V_k are the rotational and keplerian velocities, respectively, versus the fractional radius and the orbital period shows some very interesting features, in particular clear cut-off periods for the synchronization and circularization with a strong dependence on mass and evolutionary stage.

New results on the period-luminosity diagram of LPVs

Thomas Lebzelter (Institute f. Astronomy University of Vienna Türkenschanzstrasse 17 A1180 Vienna, Austria)
Ken Hinkle (NOAO/Gemini, USA)
Peter Wood (RSAA Canberra, Australia)

The period-luminosity relation of long period variables (LPVs) has been studied extensively in the past few years with the advent of large samples of light curves of these stars obtained by MACHO surveys. This lead to the discovery of at least four parallel period-luminosity sequences. We compared these findings with period and luminosity data for stars in the Globular Cluster 47 Tuc and in the Galactic field, and investigated the pulsational behaviour represented by the velocity curve at different points in the P-L-diagram. In this talk we will show the differences in velocity variations throughout the P-L-diagram and discuss the relation of period/luminosity, velocity amplitude and mass loss.

UKIRT's WFCAM and the Detection of 10 Jupiter-mass Objects

Sandy Leggett (Joint Astronomy Centre Hawaii)
The UKIDSS and Cool Dwarfs Groups ()
The WFCAM Team ()

UKIRT will be commissioning its near-infrared wide field camera, WFCAM, in fall 2004. We describe the instrument and the planned surveys, one of which, the Large Area Survey, will image 4000 sq.degrees in YJHK filters to K=18.4. This survey will extend the field brown dwarf population to temperatures and masses significantly lower than those of the free-floating T dwarf population discovered by the Sloan and 2MASS surveys - objects at 10pc as cool as 450K and as low mass as 10 Jupiter-masses (for an assumed age range of 1-5 Gyr) should be detected by WFCAM. We present synthetic YJHK colors derived from observed and modelled spectra of a variety of objects to illustrate how ultracool dwarfs will be identified in the survey and describe plans for followup spectroscopic observations of candidate T and later type dwarfs.
http://www.jach.hawaii.edu/~skl/

The NEXXUS database - X-ray properties of nearby stars

Carolin Liefke (Hamburger Sternwarte )
Jürgen H. M. M. Schmitt (Hamburger Sternwarte)

We compiled the NEXXUS database of Nearby X-ray and XUV- emitting stars. This is an X-ray equivalent to the CNS4 catalog of nearby stars. It contains the X-ray data of all stars within a distance of 25 pc. It was constructed using ROSAT data from the final all-sky survey and pointing catalogs and we have recently begun to also include data from the XMM-Newton Source Catalog. This large number of sample stars (≈1300 detections)proves to be a powerful tool to investigate the X-ray properties of the solar neighbourhood. We constructed volume-limited samples of F/G- stars, K-stars, and M-stars with detection rates greater than 90%. The analysis of these samples shows that the mean X-ray luminosity decreases for later spectral types, while the X-ray surface flux distribution appears to be independent of spectral type with a lower limit corresponding to the flux level of solar coronal holes.
http://www.hs.uni-hamburg.de/DE/For/Gal/Xgroup/nexxus

The Nearest Star: DEM Analysis of AR 8232

Li Wei Lin (Harvard-Smithsonian Center for Astrophysics)
Vinay L. Kashyap (Harvard-Smithsonian Center for Astrophysics)
Jeremy J. Drake (Harvard-Smithsonian Center for Astrophysics)

We describe the application of a sophisticated differential emission measure (DEM) reconstruction technique to contemporaneous solar data obtained from SXT,TRACE,EIT,CDS and GOES. Based on a Markov-Chain Monte Carlo algorithm originally developed for use with high resolution stellar EUV and X-ray spectra, the method is easily adapted to any combination of observations with different instruments and filters. We employ the technique to characterize the DEM in a solar active region AR 8232 (June 1998) for which data are available from all five instruments. We compare a DEM which is spatially averaged over the entire region to DEMs derived for individually resolved AR features. We will discuss the implications these results have for DEM analysis of stellar corona.
http://hea-www.harvard.edu/PINTofALE/

First Scientific Results from SuperWASP-I Commissioning: Rotation periods of Pleiades stars.

Tim Lister (University of St. Andrews)
The SuperWASP Collaboration ()

We present the first scientific results from SuperWASP-I commissioning data obtained in 2003 November/December. SuperWASP-I currently consists of 5 Canon 200mm f1.8 lenses with high quality CCDs on a robotic mount located on La Palma. Each camera covers approximately 7.8x7.8 degrees and can monitor tens of thousands of stars in the magnitude range 8 to 15. The advanced custom-built pipeline developed by the collaboration produces automatic astrometry, photometry, colours and blending analysis allowing high precision light curves to be obtained.
Observations of the Pleiades open cluster were obtained on several nights during the commissioning period in 2003 November/December. We present the results of processing these data and discuss the rotationally modulated spotted stars and other variable stars that are found.
www.superwasp.org

"Whistler" modulation envelope of the HF solar burst

Igor Litvinenko (Institute of Radio Astronomy NASU)
Oleg Litvinenko (Institute of Radio Astronomy NASU)

Radio telescope URAN-4 is a part of Ukrainian VLBI system URAN, which operates in the decameter wavelength band. The telescope is located in Odessa region (Ukraine). Phased array antenna has two orthogonal linear polarizations. The effective area of antenna is 7300 sq.m. At realization of millisecond time resolution experiments on detecting solar sporadic radio emission the radio bursts with an unusual microstructure were registered. Modulation envelope of burst intensity was quasi linearly frequency modulated signal (down chirp). Range of deviation of frequency was 33 ... 1,5 Hz. Duration of burst was 0.8 ... 2,2 s. Working frequency of observation was 25 MHz. Flux density of bursts was reached 0,1 MJy. During 3 hours was registered about 40 bursts. Others our observations of solar burst microstructure indicate that clearly expressed "whistler" modulation envelope is rare event.

Modern concepts of large solar events and stellar flares

Moissei Livshits (Institute of Terrestrial Magnetism, Ionosphere and Radio Wave Propagation of Russian Academy of Sciences)
Maria M. Katsova (Sternberg State Astronomical Institute)

An analysis of recent observations including data from TRACE and RHESSI shows that a large event on the Sun consists of one or a few impulsive episodes, eruption and post-eruptive arcades. We discuss an application of the solar experience for interpretation of new data for more energetic stellar flares. Many predictions of the developed by us gas-dynamic model of impulsive stellar flares are now observed direct-ly. For instance, it concerns to velocities of the hot and cool plasma. We show that a pulse in stellar flares is so powerful that breaks conditions of existence of two-ribbon flare. It becomes clear why post-eruptive events are practically absent on red dwarfs. We argue that rare compact gamma-ray solar flares are a prototype of impulsive stellar flares. Another kind, prolonged X-ray flares, is associated with a process of opening of the large-scale configuration when reconnection occurs at progressively higher altitudes. On the Sun giant post-eruptive arches reach as a rule a definite height and do not expand farther, while on stars (especially, subgiants) one part of such arches drifts out of the corona and another one is shrinking and falls down.

Mass-loss and Recent Spectral Variability in the Yellow Hypergiant Rho Cassiopeiae

Alex Lobel (Smithsonian Astrophysical Observatory)
Jason Aufdenberg (National Optical Astronomy Observatory, USA)
Ilya Ilyin (Astrophysikalisches Institut Potsdam, Germany)

The yellow hypergiant Rho Cassiopeiae (F-G Ia0) has recently become very active with a tremendous outburst event in the fall of 2000. During the event the star dimmed by more than a visual magnitude, while its effective temperature decreased from 7000 K to below 4000 K over about 200 d, and we directly observed the largest mass-loss rate of about 5% Msun/yr in a single stellar outburst so far.
Over the past three years since the eruption we observe a very prominent inverse P Cygni profile in Balmer H alpha, signaling a strong collapse of the upper atmosphere, also observed before the 2000 event. Continuous spectroscopic monitoring reveals that the H alpha line profile has transformed into a P Cygni profile over the past 10 months, presently signaling supersonic expansion velocities up to ca. 120 km/s in the upper atmosphere, comparable to the 2000 outburst.
We present an overview of the recent variability phases with enhanced mass-loss from this enigmatic cool pulsating star (for more information see Mercury Mag. 2004, Vol. 33, 1, 13).
http://cfa-www.harvard.edu/~alobel http://alobel.freeshell.org

Predicting the length of magnetic cycles in late-type stars

Rosario Lorente (ISO Data Center ESA Satellite Tracking Station PO Box 50727 E-28080 Madrid Spain )
Benjamin Montesinos (LAEFF, ESA Satellite Tracking Station, Madrid, Spain)

The long-term monitoring of the variation of the Ca II H and K emission lines in late-type stars, carried out at Mount Wilson and Las Campanas since 1966, has allowed the detection of activity cycles, similar to the well-known 11-year solar cycle, in some 30 stars.
Some of the most recent models developed to reproduce the different properties of the solar cycle are the so-called interface dynamo models. The newest assumption is that the poloidal and the toroidal fields are generated in different layers, the former in the convection zone and the later in the overshoot region.
We present an interface dynamo model that attempts to reproduce the length of the observed activity cycles in solar-type stars. The model has been used for predicting trends of the magnetic field intensities in the stellar interiors and linking them to the observed magnetic fluxes fB in these stars.

Searching for extrasolar planets around red giants in intermediate-age open clusters

Christophe Lovis (Geneva Observatory 51, chemin des Maillettes CH-1290 Versoix, Switzerland)
Michel Mayor (Geneva Observatory)
Stephane Udry (Geneva Observatory)

We present preliminary results from our radial-velocity survey of 72 red giants in the clump of 8 open clusters in the southern sky. The data, obtained with the CORALIE spectrograph at La Silla, have a mean precision of ca. 13 m/s and extend over about one year. Cluster membership allows precise knowledge of red giant masses, which are very uncertain for field red giants. The age of the clusters (200 Myr to 4 Gyr) involves red giant masses between 1.3 and 3.7 M_ˆ. Interestingly, the radius reached by these giant stars at the RGB tip is not a strong limitation to the existence of short-period planets. The minimum orbital period for low-mass companions around 2 M_ˆ giants (ca. 20 days) is actually much smaller than around 1.0-1.3 M_ˆ giants (ca. 200 days). The main limitation to the detection of planets will be the stellar RV jitter, which is poorly understood for giant stars. Our first results show that two thirds of the stars have a radial-velocity dispersion below 50 m/s, with a peak at about 25 m/s. We discuss the dependence of the RV dispersion on the color index and the position in the H-R diagram. Some interesting candidates are also presented.

A study on the flux-flux and activity-rotation relationships for late-type stars members of young stellar kinematic groups

Javier López-Santiago (Universidad Complutense de Madrid)
David Montes (Universidad Complutense de Madrid)
M.José Fernández-Figueroa (Universidad Complutense de Madrid)

We present here our ongoing study on the spectroscopic properties of the young active stars members of young moving groups Local Association (Pleiades moving group, 20 - 150 Myr), IC 2391 supercluster (35 Myr), Ursa Major group (Sirius supercluster, 300 Myr), Hyades supercluster (600 Myr) and Castor moving group (200 Myr). High resolution echelle spectra of 140 late-type stars have been taken during several observing runs from 1999 - 2004. In this contribution we analyse the flux-flux and activity-rotation relationships for the chromospherically active stars of the sample. With this aim, each optical chromospheric activity indicator from Ca ii H & K to infrared triplet (IRT), including Balmer series, has been used. Both projected rotation (v sini) determined by us and photometric period (P_phot) from the literature have been used in the activity-rotation relationship. We discuss the different behavior of these relationships in groups of stars with different age and the dependence on stellar parameters of the saturated regime.
http://www.ucm.es/info/Astrof/users/jls

Evolution of Coronal Structures in Late-Type Stars

Antonio Maggio (INAF - Osservatorio Astronomico di Palermo)
One of the basic questions about the physics of stellar coronae is whether their thermal structures can be explained using standard coronal loop models as building blocks, as suggested by early observations of the solar corona. A related issue is how the activity level is linked to the characteristics of coronal structures, for stars of different age and with different rotation/convection regimes. In this contribution I will present a comparison between the coronal properties of the Sun and other selected late-type stars, including naked T-Tauri stars, main-sequence stars, and Hertzsprung gap giants, observed with the Chandra and XMM-Newton high-resolution spectrometers. The information derived from emission measure analysis of their X-ray spectra will be used to shed light on how the X-ray luminosity--coronal temperature relationship is established.
http://www.astropa.unipa.it/~maggio

The L to T Dwarf Transition

Mark Marley (NASA/Ames Research Center)
At least three explanations have been proposed to explain the rapidity of the L to T dwarf transition. These ideas have included a continuously sinking, thin cloud layer, horizontally patchy cloudiness, and a rapid increase in the cloud sedimentation efficiency at a given effective temperature. With the advent of measured parallaxes for a large number of late L through early T dwarfs we now know that the transition takes place at roughly constant effective temperature, which places severe constraints on all of the proposed mechanisms. In addition high quality spectral datasets from Spitzer Space Telescope/IRS and IRTF/SpeX, now provide a wealth of new information about objects at the L to T transition and substantially increase the wavelength range over which the effects of clouds can be modeled. After comparing our model spectra with these datasets I will discuss how well the various mechanisms can account for the observed spectra of L and T dwarfs and other observables. In addition I will consider how gravity signatures among the L/T transition objects can further constrain the transition mechanism. I will argue that the preponderance of evidence favors models in which the cloud behavior undergoes fundamental changes at the transition. Mass or gravity selection effects do not adequately account for all of the available data.

Effects of convective overshooting in the PMS evolution of intermediate mass stars

João Marques (Centro de Astrofísica da Universidade do Porto/Grupo de Astrofísica da Universidade de Coimbra)
João Fernandes (Grupo de Astrofísica da Universidade de Coimbra)
Mário João P. F. G. Monteiro (Centro de Astrofísica da Universidade do Porto)

We discuss the new results on the effects of convective overshooting in the PMS evolution of intermediate mass stars. These effects are extremely important in the end of the PMS, when the abundances in CNO elements approach the equilibrium in the centre. A moderate amount of overshooting produces, as the star approaches the ZAMS, an extra loop in the evolutionary tracks on the HR diagram; the amount of overshooting needed to produce the loop decreases with the stellar mass.
An interesting feature is that there is a very well defined amount of overshooting (for a given stellar mass and chemical composition) beyond which a loop is produced; for smaller amounts of overshooting such a loop does not take place and the evolutionary tracks are similar to the ones obtained by Iben (1965).
We discuss the reasons for this behaviour and argue that it can provide a crucial observational test for convective overshooting in the core of intermediate mass stars.

Doppler imaging and differential rotation of young open cluster stars

Stephen Marsden (Institute for Astronomy, ETH Zurich)
Brad Carter (University of Southern Queensland)
Jean-Francois Donati (Observatoire Midi-Pyrenees)

Young open clusters offer a large sample of solar-type stars with high rotational velocities suitable for Doppler imaging. This makes them ideal laboratories for studying surface differential rotation (measured though Doppler imaging techniques) on a range of solar-type stars with differing masses and/or rotation rates. We present Doppler images and differential rotation measurements of two solar-type stars in the southern open clusters IC 2391 and IC 2602 along with a list of other suitable targets from the clusters.

Oscillatory phenomena in flares from active cool stars

Mihalis Mathioudakis (Queens University Belfast)
Shaun Bloomfield (Queens University Belfast)
Vik Dhillon (University of Sheffield)

Current theories of atmospheric heating are grouped into two main categories. The first holds for current dissipation following reconnection events in the form of flare, microflare and nanoflare activity, while the second suggests that the heating is driven by high frequency MHD waves. We show that an oscillatory behavior is often detected during flare events, suggesting that these two groups of theories may actually be linked. Our results are based on high cadence (0.1 sec) Ultracam observations of active flare stars, obtained simultaneously in three different wavelength bands.
http://star.pst.qub.ac.uk

Evidence for coronal opacity on AB Dor

Marco Matranga (Queen's University Belfast)
Mihalis Mathioudakis (Queen's University Belfast)
Hilary R. M. Kay (Mullard Space Science Laboratory)

The coronal spectra of the Sun and cool stars contain contributions from plasmas at different temperatures. A widely used assumption associated with these techniques is that transition region and coronal emission is optically thin. Although this may be a good approximation for the vast majority of lines, a number of resonance transitions exist with sufficiently large oscillator strengths to lead to high optical depth. We have carried out a detailed study of AB Dor and find evidence for opacity in its active corona. The implications of these finding will be discussed.

Helium line formation in a Solar Active Region

Pablo Mauas (Instituto de Astronomia y Fisica del Espacio - CONICET)
Andretta, V. (Osservatorio Astronomico di Capodimonte)
Falchi, A. (Osservatorio Astrofisico di Arcetri)

We build semiempirical models of the chromosphere and transition region of a solar active region, based on simultaneous observations of the Ca II K, H-alpha and Na D lines, as well as the He I lines at 10830, 5874 and 584 A and the He II line at 304 A. These lines were observed during a coordinated campaign between ground based and SOHO instruments (SOHO JOP 139).
We also obtained an estimate of the UV radiation illuminating our modeled region, combining observations from SOHO instruments (CELIAS, SEM and EIT) and theoretical tools, and therefore we can constrain the formation of the He lines and the He abundance.
We found that it is possible to explain the observations with the canonical value of A[He]=0.1, but either a strong irradiation or a low microturbulence is needed. Alternatively, the observations would imply a higher value of the Helium abundance.
http://www.iafe.uba.ar/mauas

The changing corona of LQ Hya

Thomas McIvor (University of St. Andrews)
Moira Jardine (University of St. Andrews)
Andrew C. Cameron (University of St. Andrews)

We have used Zeeman-Doppler maps of the surface magnetic field of the rapidly rotating K2 star LQ Hya to extrapolate the coronal field, assuming it to be potential. Using the data sets from the observations in 2000 and 2001, chosen for their excellent phase coverage, we show how the global structure of the magnetic field can drastically change drastically in the space of one year. In 2000 Dec the large scale field resembled a tilted dipole, with most of the open field emerging in two mid latitude regions separated by 180 degrees of longitude. One year later, most of the open field emerged at the pole, and the large scale field most closely resembled an aligned dipole albeit with a significant contribution from many smaller scale east-west arcades of magnetic field lines. This appears to be quite different to what is seen on the sun, where the emergence of many east-west bipoles occurs towards cycle maximum, when the large scale heliosphere field resembles a tilted, not an aligned dipole. We have also modelled the X-ray emission (assuming an isothermal corona) and find that despite the changes in the field structure, the magnitude and the rotational modulation of the emission measure (Log(em)=51.15 cm-3) is largely unchanged. While the emission measure is close to observed values the density (Log(n) = 9.8 cm-3) is somewhat lower.

MHD waves in Stellar Atmospheres

Andrew McMurry (Centre of Mathematics for Applications University of Oslo)
Using an MHD code, we are modelling the behaviour of waves in the stellar atmosphere. We have new boundary conditions to our models that allow all magnetic waves to pass through. This is important when looking for physical reflections in the atmosphere, as reflections in the numerical boundary would confuse the issue. As waves are an important candidate for chromospheric and coronal heating, it is important to know as much as possible about their behaviour.

X-ray observations of the young open cluster Blanco 1

Giuseppina Micela (INAF - Oss. Astronomico di Palermo)
I. Pillitteri, F. Reale (DISF&A, Universita` di Palermo)
F. Damiani, S. Sciortino, F.R. Harnden, Jr. (INAF- OAPA (Italy) & CFA (USA))

We present results of X-ray spectroscopy and time variability analysis of the stars of young open cluster Blanco 1 observed with XMM/Newton.
All dF and dG and 80% of dK and dM members in the field-of-view have been detected. The spectral analysis of brightest solar type stars indicates that two thermal components at 0.3 and 1 keV well explain the emission of their coronae, while a late-A star shows a much more soft emission suggesting a different mechanism for its origin. X-ray variability is common in Blanco 1 stars, with very low mass dM-type stars being more flaring than solar mass stars. These latter show in some cases smooth variations. The detailed analysis of two flares in a cluster star allows us to derive the morphology of the flaring structure.

Constraints on the length of a flare loop from oscillations detected during a stellar X-ray flare on AT Mic

Urmila Mitra Kraev (MSSL - University College London)
L. K. Harra (MSSL - University College London)

Analysing an X-ray light curve of the late-type star AT Mic, observed by XMM-Newton, with Fourier and Wavelet Analysis, a flare shows sustained, oscillating emission during flare maximum. We interpret these oscillations as density perturbations in the flare loop. Recent results from a numerical model suggest that they are associated with standing acoustic waves within the loop. The model gives a relationship between the oscillation period, the loop length and the average plasma temperature. The plasma temperature of the AT Mic flare is known from the observed X-ray spectrum. Applying this relationship, the loop length of the flare can be estimated. First results give an oscillation period of 700s, which with an average temperature of 24 MK imply a loop length of 500 Mm, which is in the order of 1 stellar radius.

Flare stars among K dwarfs members of young stellar kinematic groups

David Montes (Universidad Complutense de Madrid, Dpto. Astrofisica)
D. Montes (Universidad Complutense de Madrid)
J. López-Santiago, I. Crespo-Chacón, M.J. Fernández-Figueroa (Universidad Complutense de Madrid)

During the last years (1999 - 2004), our group has been studying the spectroscopic properties of a large sample of stars members of the young stellar kinematic groups: Local Association (Pleiades moving group, 20 - 150 Myr), IC 2391 supercluster (35 Myr), Ursa Major group (Sirius supercluster, 300 Myr), Hyades supercluster (600 Myr) and Castor moving group (200 Myr). The high resolution spectroscopic observations used in this study allow us to better determine radial velocities, chromospheric activity and lithium abundance of these objects. The chromospheric activity level of these stars has been analysed using the information provided for several optical spectroscopic features (from the CaII H & K to CaII IRT lines). Here we report the detection of flare and flare-like events in some of the K dwarfs of the sample such as PW And, BD+17 232, BD+20 1790, DK Leo, and FP Cnc.
http://www.ucm.es/info/Astrof/users/dmg/dmg.html

Photospheric abundance peculiarities in chromospherically active stars

Thierry Morel (Osservatorio Astronomico di Palermo, Piazza del Parlamento, 1,90134 Palermo, Italy)
Giusi Micela (Osservatorio Astronomico di Palermo)
Fabio Favata (ESTEC)

We present the physical parameters and photospheric abundances of 14 single-lined chromospherically active binaries, and show that increasingly peculiar abundance ratios are observed with higher chromospheric/coronal activity level (best illustrated in the case of oxygen). We argue that NLTE effects whose magnitude largely exceeds what is anticipated for inactive stars may be responsible, although more general shortcomings in our modelling of the atmospheres of cool stars cannot be ruled out.
http://www.astropa.unipa.it/~morel/

The ELODIE planet search survey global detection limit

Dominique Naef (ESO Santiago & Geneva Observatory)
Michel Mayor (Geneva Observatory)
Stephane Udry (Geneva Observatory)

We present the global detection limit of the ELODIE planet search survey after 10 years of observations. 50% and 90% detection thresholds in the secondary mass versus orbital period diagram have been obtained trough detailed numerical simulations. We also show the impact of various stellar properties (colour, metallicity, rotation) on the detection sensitivity. The detection limits allow us to correct the observed rate of stars hosting planets for observational biases. We present the corrected rate for the ELODIE survey.
http://www.sc.eso.org/~dnaef/index.html

Hyper Digital Sky Survey: In search of faint high proper motion stars

Tadashi Nakajima (National Astronomical Observatory of Japan)
We are planning a wide field CCD survey at i and z using an existing 2m class telescope in search of high redshift quasars, low temperature brown dwarfs, and faint high proper motion objects. In this talk, we concentrate on the discussion of the faint high proper motion stars, which include K, M subdwarfs in the Galactic Halo. We expect to detect some 400 subdwarfs per square degree, among which 0.2 subdwarfs are within 200 pc of the Sun. If zero metal subdwarfs which are not bound by the Galaxy exist, the bottom of population III subdwarf sequence will be detectable out to 600 pc with proper motions greater than 1"/yr.

Direct imaging of sub-stellar companions around young nearby stars

Ralph Neuhaeuser (AIU Uni Jena Schillergaesschen 2-3 D-07745 Jena, Germany)
Eike Guenther (TLS Tautenburg)
Guenther Wuchterl (AIU Jena)

Our deep, high-resolution imaging survey for faint, close companions to young nearby pre-MS or ZAMS stars within 100 pc has resulted in three confirmed companions: TWA-5 B, HR 7329 B, and GSC 8047 B. Three brown dwarfs found among almost 100 stars observed corresponds to a frequency of a few brown dwarfs with separation outside of 50 AU. Also, we can set a hard upper limit on the number of massive planets at very wide separations.
www.exoplanet.de

Flare and Quiescent X-ray Emission from Sigma Gem

Raanan Nordon (Technion, Israel)
Ehud Behar (Technion, Israel)
Manuel Guedel (Paul Scherrer Institute, Switzerland)

We have analyzed two different high-resolution, grating, x-ray observations of the RS-CVn binary system sigma-Gem, in flaring and quiescent states. Physical measurements of chemical abundances, emission measure distributions and electron densities during the two states are compared. We present an ion-by-ion fit to the spectra with a good match to both observations. Implications for the chromospheric evaporation scenario of coronal flares are discussed.

Exploring the use of VO to diagnose spot properties on M dwarfs

Douglas O'Neal (Allegheny College)
Manfred Cuntz (University of Texas-Arlington)
James E. Neff; Steven H. Saar (Col. of Charleston; Harvard-Smithsonian CfA)

In several studies, we have measured absolute areas and temperatures of starspots on magnetically active stars using absorption bands of TiO. In active stars where T_eff>4200 K, these features arise only in the cool spotted regions (the molecule is dissociated in the warmer photosphere). This method faces difficulty if the active star's photosphere shows TiO absorption (e.g. active M dwarfs, for which photometry clearly indicates of dark spots). To extend our spectroscopic measurements to active M dwarf stars, we obtained R∼60,000 spectra of eight such stars covering three absorption bands of VO (near 7400, 7900, and 8600 Å.) These bands are sensitive to lower temperatures than TiO; in dwarfs they first appear at spectral type M5-6, as opposed to K7-M0 for TiO. Their presence in warmer M dwarfs thus potentially serves as an unambiguous signal of cool spots. We find that the weaker VO features are difficult to detect in warmer M dwarfs. We discuss limits this implies for the presence of starspots on these stars and for the applicability of VO spectroscopy for observing them.

Warm water vapor envelope in the supergiants alf Ori and alf Her and its effects on the mid-infrared apparent size

Keiichi Ohnaka (Max-Planck-Institut fuer Radioastronomie)
We present a possible interpretation for the increase of the angular diameter of the supergiants alf Ori and alf Her from the K band to the 11 micron region and the high-resolution 11 micron spectra without any salient spectral features. The angular diameters as well as the high-resolution spectra of alf Ori and alf Her obtained in the 11 micron region can be reproduced by a warm water vapor envelope. While prominent absorption due to H2O can be expected from this dense, warm H2O envelope, the absorption lines can be filled in by emission from the extended part of the envelope. This effect leads to a significant weakening of the H2O lines in the 11 micron region, and makes the observed spectra appear to be rather featureless. However, the emission due to H2O lines from the extended envelope leads to an increase of the apparent size in this spectral region. The observed angular diameter and the high resolution spectra of alf Ori and alf Her in the 11 micron region can be best interpreted by the H2O envelope extending to 1.4 -- 1.5 stellar radii, with a temperature of 2000K and a column density of H2O of the order of 10²⁰ cm^-2.

Radio Observations of Brown Dwarfs

Rachel Osten (NRAO)
Suzanne L. Hawley (University of Washington)
Tim Bastian, I. Neill Reid (NRAO, STSci)

The detection of magnetic activity signatures in very late-type dwarfs (late M -> L) is puzzling, as models suggest that the highly neutral atmospheres should be incapable of sustaining the kinds of magnetic stresses which pervade the outer atmospheres of solar-like stars (G, K, early M dwarfs). And yet, Halpha, X-ray, and radio emission is clearly detected, along with flare-like variability. Previous studies have claimed that radio luminosity relative to bolometric luminosity actually increases toward later L & T spectral types, yet this is based on only a few detections. Recently, we have undertaken a project to investigate the cause of radio emission from brown dwarfs, and determine how common this phenomenon is. We present preliminary results using sensitive radio observations with the Very Large Array, using a two-pronged approach: deep probes of objects previously detected during both flares and quiescence; and a volume-limited survey of L & T dwarfs accessible with the VLA out to 13 pc.

The X-ray emission from Young Stellar Objects in the rho Ophiuchi dark cloud as seen by XMM-Newton

Hideki Ozawa (Laboratoire d'Astrophysique de Grenoble)
Nicolas Grosso (Laboratoire d'Astrophysique de Grenoble)
Thierry Montmerle (Laboratoire d'Astrophysique de Grenoble)

We observed the dense core F of the rho Ophiuchi dark cloud, an active star-forming region located at ≈140 pc, with the XMM-Newton Observatory with an exposure of 33 ks. We detect 87 X-ray sources within the 30' diameter field-of-view of XMM-Newton. We compare the positions of XMM-Newton X-ray sources with previous X-ray and infrared (IR) catalogs: 25 new X-ray sources are found from our observation; 43 X-ray sources are detected with both the XMM-Newton and Chandra observatories; 68 XMM-Newton X-ray sources have near-IR counterparts from comparison with 2MASS catalog. We show that XMM-Newton and Chandra have comparable sensitivity for point source detection when the exposure tie is 30 ks. We detect X-ray emission from 7 Class I sources, 26 Class II sources, and 17 Class III sources. The X-ray detection rate of Class I sources is very high (64 %), which is consistent with previous Chandra results on this area. We show that 15 X-ray sources are new class III candidates. We also detect X-ray emission from two bona fide brown dwarfs, GY310 and GY141, out of 3. We extracted X-ray light curves and spectra from these YSOs, and find some of them showed weak X-ray flares.

Modeling the variability of the Sun as observed by Virgo/SoHO: effects of stellar activity on the detection of planetary transits

Isabella Pagano (INAF - Catania Astrophysical Observatory)
A.F. Lanza (INAF - Catania Astrophysical Observatory)
M. Rodono' (INAF - Catania Astrophysical Observatory)

The time series of total solar irradiance (TSI) and optical spectral irradiance at 402, 500 and 862 nm (SSIs) obtained by the VIRGO experiment on board the satellite SoHO are analysed in order to model their variability in the framework of a purely stellar-like approach. The different time scales of variability are estimated by means of the pooled variance method revealing the growth and decay of sunspots and faculae in active regions, as well as their rotationally modulated visibility. We show that the determination of the rotation period of the Sun from the time modulation of the TSI and SSIs is made difficult by the short lifetimes of photospheric brightness inhomogeneities in comparison to the rotation period. In fact, only during the phases with the lowest level of activity of solar cycle 23, when the variability is dominated by long-lived faculae, it is possible to determine the truly solar synodic period. The simultaneous modelling of the rotational modulation of the TSI and SSIs can be performed by means of a simple stellar-like approach. Our model yields residuals about 20-30 times smaller than the amplitudes of the TSI and SSI variations at all the phases of the 11-yr activity cycle. We discuss the advantages and the drawbacks of applying our model to other stars, in the framework of the characterization of the stellar activity signal in the light curves searched for extrasolar planet transit signatures.
http://web.ct.astro.it/coolstars/ipa/isabellapagano.htm

Lithium in intermediate age and old open clusters

Roberto Pallavicini (Osservatorio Astronomico di Palermo )
Sofia Randich (Osservatorio Astrofisico di Arcetri)
Paola Sestito (Dip. Astronomia, Universita` di Firenze)

Contrary to standard models of internal mixing in stars, lithium is observed to suffer slow depletion during evolution on the main sequence, with virtually no observed dependence on metallicity. Moreover observations of field stars and of the solar-age solar-metallicity old cluster M67 have revealed a factor of 10 scatter in the Li abundances of solar-type stars as old as or older than the Sun. We review recent results on Li abundances obtained by us for late-type stars in open clusters ranging in age from the Hyades (600 Myr) to nearly 10 Gyr. We also report preliminary results of Li abundances obtained with the multi-object spectrograph FLAMES at VLT UT2 for the intermediate age and old open clusters NGC 2506, Melotte 66 and Collinder 261. We focus in particular on FLAMES observations of Collinder 261, one of the oldest open clusters.
http://www. astropa.unipa.it

Substellar Mass Companion Detection Around Young Stars

Diane Paulson (University of Michigan)
The presence of stellar activity has been shown to interfere with planet detection. Young stars, in particular, are strongly affected, but they are a very important population of stars with regard to the understanding of the evolution of planetary/brown dwarf systems. Current radial velocity surveys disregard the youngest stars in planet searches because most planetary systems will be hidden within the noise of activity. I will discuss the types of substellar mass companions which can be detected around young stars and present the early findings of my current radial velocity search for substellar mass companions around young stars.

Composing stellar coronae with solar-like coronal structures: the F_x-vs.-HR and the pressure-vs.-temperature diagrams.

Giovanni Peres (Dip.S.F.A. -sez. Astronomia - Univ. di Palermo )
S. Orlando (INAF - Oss.Astr.Palermo "G.S. Vaiana")
F. Reale (Dip.S.F.A. -sez. Astronomia - Univ. di Palermo )

We show that stellar coronae can be composed of structures like those in the solar corona; we use large sets of ROSAT/PSPC observations, and of solar X-ray data taken with Yohkoh/SXT. We analyzed solar coronal data at various phases of the cycle and all kinds of coronal structures, from flares to the background corona. The X-ray surface flux (F_x) strongly correlates to the hardness ratio (HR) in stellar coronae, in the solar corona at all phases of the cycle, and in the individual solar coronal structures, all along the same law. We thus claim that coronae of late type stars are made of X-ray structures very similar to solar ones. In this view, the fraction of stellar surface covered with active regions and with their bright cores increases with activity. The most active stars can be explained only with the additional presence of several flare-like structures at any time. From the F_x vs. HR correlation (F_X ≈ T⁶) we derive new laws relating temperature, pressure, volumetric heating and loop length of the coronal plasma. We claim that these laws just imply a physical mechanisms acting on all the coronal structures from their emergence to their dissipation.
http://www.astropa.unipa.it/~peres

The F_x-HR diagram and the pressure-temperature correlation as tools to interpret solar and stellar coronae.

Giovanni Peres (Dipartimento di Scienze Fisiche ed Astronomiche - sez. di Astronomia Universita` di Palermo - ITALY)
Salvatore Orlando (INAF - Osservatorio di Palermo "G.S.Vaiana" - Palermo - ITALY)
Fabio Reale (Dipartimento di Scienze Fisiche ed Astronomiche - sez. di Astronomia Universita` di Palermo - ITALY)

We show that stellar coronae can be composed of X-ray emitting structures like those in the solar corona, using a large set of ROSAT/PSPC observations of late-type-stars, and a large set of solar X-ray data collected with Yohkoh/SXT pertaining to various phases of the cycle and various kinds of X-ray coronal structures, from flares to the background corona. The X-ray surface flux (F_x) is strongly correlated to the spectral hardness ratio (HR) in stars, on the Sun at all phases of the cycle, and in each solar coronal structure, hinting that coronae of late type stars are made of structures like the solar ones. The fraction of stellar surface covered with active regions and their bright cores increases with activity, the most active stars requiring the additional presence of several flares at any time. The F_x vs. HR correlation (F_x ≈ T⁶) leads to laws relating the temperature, pressure, volumetric heating and characteristic loop length of the coronal plasma, on all the late type stars We claim that these laws are the effect of physical mechanisms driving the coronal structures of all the late-type stars from the emergence of new magnetic structures to their dissipation.
http://www.astropa.unipa.it/~peres

Differential rotation of solar-type stars

Pascal Petit (Max-Planck Institut für Aeronomie)
Doppler and Zeeman-Doppler Imaging enable one to analyze the relative motion of active regions on the surface of solar-type stars, under the effect of differential rotation. From new measurements of the rotational shear on a small sample of objects, we confirm the increase of shear level with surface temperature reported by Collier Cameron (2002) and propose that tidal torques exerted on components of close binary systems significantly reduce the intensity of surface differential rotation.
http://webast.ast.obs-mip.fr/people/petit

Large-scale magnetic geometry of the G8 dwarf xi Bootis A

Pascal Petit (Max-Planck Institut für Aeronomie)
We investigate the magnetic geometry of the active G8 dwarf xi Bootis A, from spectropolarimetric observations obtained in the summer of 2003 with the MuSiCoS échelle spectropolarimeter at the Télescope Bernard Lyot (Observatoire du Pic du Midi, France). We repeatedly detect a photospheric magnetic field, with periodic variations consistent with rotational modulation of period 6.43 days. A direct modelling of the circularly polarized line profiles suggests that the large-scale field is constituted of two mains components, with an inclined dipole and a large-scale toroidal field. This result provides a confirmation, based on independent modelling techniques, to previous detections of large-scale azimuthal fields on cool active stars achieved with the help of Zeeman-Doppler Imaging.
http://webast.ast.obs-mip.fr/people/petit

Magnetic mapping of solar-type stars

Pascal Petit (Max-Planck Institut für Aeronomie)
Jean-François Donati (Observatoire Midi-Pyrénées)

Zeeman-Doppler Imaging is a tomographic technique that enables one to reconstruct vector magnetograms of fast-rotating solar-type stars from time-series of polarized spectra. The surface distribution of magnetic regions, their short-term evolution over a few weeks or their secular variations under the action of activity cycles provide key information about the underlying dynamo processes at work in cool active stars. After summarizing the main results obtained in this framework, I will detail the new fields of investigation that will become accessible in the near future thanks to the larger spectral coverage and better sensitivity of the ESPaDOnS spectropolarimeter now available at CFHT.
http://webast.ast.obs-mip.fr/people/petit

Measuring empirical properties of new brown dwarfs in eclipsing binary systems

David James Pinfield (Astrophysics Research Institute, Liverpool John Moores University, 12 Quays House, Egerton Wharf, Birkenhead, CH41 1LD, UK)
Hugh R. A. Jones (Liverpool John Moores University)
Iain A. Steele (Liverpool John Moores University)

I will describe a new project to provide empirical mass-age-magnitude data for brown dwarfs. This data will come from young fully eclipsing close binary systems containing a low-mass star primary and a brown dwarf secondary. Many such systems will be identified by the new breed of ultra-wide-field transit surveys (such as the UK SuperWASP survey) that are currently hunting for planet transits. For young binary systems, the brown dwarf companions will be relatively bright and it will be possible to measure their brightness from followup NIR light curves - by measuring the decrease in brightness when the brown dwarf goes behind the primary. Also, a large fraction of young field stars are members of kinematic moving groups - young groups of stars with a common space motion, believed to represent a slowly expanding coeval population that has not had time to become phase mixed with the disk. By measuring the space motions of the new binaries, moving group membership can be established, and binary (and hence brown dwarf) ages accurately constrained. Brown dwarf masses will come from radial velocity curves, after deconvolving orbital and activity induced signatures.

The Solar Convection Zone Depth Problem

Marc Pinsonneault (Ohio State University Dept. of Astronomy 140 W. 18th Ave. Columbus, OH 43210 USA)
John Bahcall, Aldo Serenelli (Institute for Advanced Studies)
Sarbani Basu (Yale University)

There have been recent proposed downwards revisions in the absolute solar metal abundance, especially for the lighter metals (C, N, O, and Ne). In this poster we examine the impact of such a lower metallicity on the properties of solar models. We find only a modest change in the inferred solar neutrino fluxes. However, both the sound speed profile and the surface CZ depth are significantly affected, and solar models constructed with low metal abundance are in conflict with solar data. The magnitude of the discrepancy between theory and observation depends on the opacity interpolation method, which suggests that a finer opacity mesh is required for precise solar models. We examine the major theoretical error sources for the seismic solar model properties. An increase in the opacity at the convection zone base could resolve the conflict between theory and observation.

VLT/UVES spectroscopic analysis of C-rich Fe-poor stars

Bertrand Plez (GRAAL)
T. Masseron (ESO and GRAAL)
F. Primas (ESO)

A new class of carbon-rich stars was revealed by large surveys of very metal-poor objects. The abundance peculiarities of the more metal-rich CH-stars, are commonly explained by mass-transfer from a more evolved companion. We present abundances determined from high-resolution and high signal-to-noise spectra obtained with the VLT2/UVES instrument. Our analysis of carbon enhanced objects includes both CH stars and more metal-poor objects, and we explore the link between the two classes. We also discuss preliminary results of our ongoing radial velocity monitoring.

Evolution of magnetic activity in young stars: new insights from the Chandra Orion Ultradeep Project

Thomas Preibisch (Max-Planck-Institut fuer Radioastronomie Auf dem Huegel 69 D-53121 Bonn Germany)
Eric D. Feigelson (Pennsylvania State University, USA)
The COUP Team ()

The Chandra Orion Ultradeep Project (COUP) is based on a unique 10 day (850 ksec), nearly continuous observation of the Orion Nebula Cluster with Chandra/ACIS. It provides the most comprehensive dataset ever acquired on the X-ray emission of normal stars. More than 1600 point sources are detected, and 562 of these can be reliably identified with optically well characterized cluster members. With a detection limit of Lx = 10^27.5 erg/sec for lightly absorbed sources, we detect X-ray emission from more than 90% of the late-type (G-M) cluster stars. We will present the main results of our detailed statistical analysis of the dependencies of the X-ray properties on other parameters like stellar mass, age, rotation, and accretion rates. The temporal evolution of the X-ray properties is studied in two ways, first within the age range covered by the cluster (from class I protostars to post T Tauri stars), and second by comparison with other well defined samples of (young) stars.
http://www.mpifr-bonn.mpg.de/staff/tpreibis/

Microvariability and Oscillations of Late-Type Giants

Heather Preston (USAFA)
Hans Bruntt (USAFA; Aarhus U.)
Derek Buzasi (USAFA)

Since the failure of the main mission of the Wide Field Infrared Explorer (WIRE) satellite, launched by NASA in March 1999, its star tracker has been extensively used for asteroseismology of bright objects (see, e.g, Buzasi 2002; Buzasi et al. 2004). WIRE observations of K giants (e.g., α Boo, Retter et al. 2004) have revealed the presence of low-level variability which is at least quasiperiodic, and which is suggestive of p-mode oscillations.
The WIRE mission was terminated in late 2000, but restarted in November 2003. In the most common operating mode, WIRE simultaneously observes a primary target and up to four secondary targets located within an 8-degree patch on the sky. Since the secondary targets are chosen to be the brightest targets within the field, the majority of them are giant stars. In this paper, we present preliminary results from this unbiased sample of late-type giants.

XMM-Newton observations of the flaring star YZ CMi: Temperature, Emission measure and abundance determination

Ton Raassen (SRON National Institute for Space Research)
Rolf Mewe+ (SRON National Institute for Space Research)

We present the analysis of the X-Ray spectrum of the flaring M-dwarf YZ CMi (M4.5 V) observed by XMM-Newton. The spectra were pipelined using SAS-version 5.4.1. The lightcurve shows a quiescent period and flaring activity during the observation. Apart from individual flares and the short time interval of "flare-rising", the two time intervals of quiescence and of coronal activity were investigated separately, to search for differences in temperature, density and abundances between the two states.Beside individual line diagnostics, the spectra were diagnosed by means of SPEX in combination with MEKAL, applying a multi-temperature fitting as well as a continuous smooth DEM-modeling method.
+ Rolf Mewe deceased 4 May 2004

Deep Optical and Near-IR Imaging Survey of the eta Cha Young Cluster

Sarah Ragan (University of Michigan)
Karl Haisch Jr. (University of Michigan)
Ray Jayawardhana (University of Michigan)

The young (≈ 6-9 Myr) eta Chamaeleontis cluster possesses a number of unique characteristics that make it an excellent subject of star-formation studies. It lies only 97 pc away, isolated from any significant molecular material, and is much more compact (0.5 deg) than other clusters of this type. To date, 18 cluster members are known, however, several lines of evidence-- such as radial counts of faint stars, initial mass function calculations, and the anomalous X-ray luminosity function-- suggest that 20-40 additional cluster members should be found within 15 arcmin of eta Cha. In addition, there may well be a coeval population of brown dwarfs. We present the results of our recent deep optical and near-infrared (R I J K) imaging survey of a 30' x 30' region using the Magellan 6.5-meter and Cerro Tololo 4-meter telescopes for companions to known members and new candidate brown dwarfs down to and below the deuterium burning limit in the nearby eta Chamaeleontis cluster.
http://www.astro.lsa.umich.edu/~seragan

Chemical abundances and Li depletion in the open cluster M67

Sofia Randich (INAF-Osservatorio di Arcetri)
Francesca Primas (European Southern Observatory)
Paola Sestito (University of Firenze)

According to model predictions, the amount of mixing in stellar interiors, and thus lithium depletion, should be affected by the star chemical composition. Using UVES-VLT high quality spectra, we have obtained abundances of alpha and Fe-peak elements in several unevolved members of the solar age cluster M 67. The results will be presented and discussed; in particular, we will discuss whether the large star-to-star scatter in Li abundances seen among solar-type cluster members can be explained by small differences in their chemical composition.

Planning your Observations with the Spitzer Space Telescope

Luisa Rebull (JPL/Spitzer Science Center/Caltech)
Spitzer Observer Support Team (JPL/Spitzer Science Center/Caltech)

The Spitzer Space Telescope (formerly SIRTF) was launched in August 2003. It has three science instruments: (1) the Infrared Array Camera (IRAC), which images at 3.6, 4.5, 5.8, and 8 microns; (2) the Infrared Spectrograph (IRS) with resolutions of ≈60 and ≈600, from ≈5 to ≈40 microns; and (3) the Multiband Imaging Photometer for Spitzer (MIPS), which images at 24, 70, and 160 microns. Early studies of stars, star formation, and the interstellar medium are already in press, and promise to provide a wealth of new and interesting results. The next call for proposals for Spitzer will be issued in Fall 2004; you need to use a tool called SPOT to prepare your observations and submit your proposal. This poster provides a quick overview of observation planning for your Spitzer observations! For more information, find us on the web at http://ssc.spitzer.caltech.edu/ .
http://ssc.spitzer.caltech.edu/

Stellar Rotation in Young Clusters: The First 4 Million Years

Luisa Rebull (JPL/Spitzer Science Center/Caltech)
S. C. Wolff (NOAO)
S. E. Strom (NOAO)

To investigate what happens to angular momentum during the earliest observable phases of stellar evolution, we combined our measurements of periods (P), projected rotational velocities (v sin i), and supporting data on K5-M2 stars (corresponding to masses 0.25 to 1 Msun) with those published in the literature for the Orion Nebula Cluster and environs, rho Oph, TW Hydra, Taurus-Auriga, NGC 2264, Chamaeleon, Lupus, and eta Cha. We combine these measures of rotation with the derived values of stellar R (as determined from L_bol and T_eff) to compare the data with two extreme scenarios for the evolution of PMS angular momenta: conservation of stellar angular velocity and conservation of stellar angular momentum. Both the P and v sin i datasets suggest that a significant fraction of all PMS stars must evolve at nearly constant angular velocity during the first 3-5 million years after they begin their evolution down convective tracks. Hence, the angular momenta of a significant fraction of PMS stars must be tightly regulated during the first few million years after they first become observable. This result seems surprising at first glance, because observations of young main sequence stars reveal a population (30-40%) of rapidly rotating stars that must begin to spin up at ages t « 5 Myr. To determine whether these apparently contradictory results are reconcilable, we make use of simple simulations and find that a modest population (30-40%) of PMS stars could in fact be released within the first 1 Myr and still produce period distributions statistically consistent with the observed data.
http://spider.ipac.caltech.edu/staff/rebull/

Monitoring Altair's Far-Ultraviolet Emission Lines for Variability Over a Stellar Rotation Period

Seth Redfield (McDonald Observatory, University of Texas)
Jeffrey L. Linsky (JILA, University of Colorado and NIST)

Ultraviolet and X-ray observations show that high temperature plasma is present in the outer atmospheres of late-type dwarf stars including late A-type stars. Aside from the detection of coronae in late-A stars and the emission rates from these hot plasmas, we know very little about their structure and heating mechanisms. The Far Ultraviolet Spectroscopic Explorer (FUSE) has the unique capability to provide new information on both of these topics. FUSE can Doppler image rapidly rotating late-A stars in lines of CIII and OVI. If the hot plasma is located primarily in bright active regions, the shapes of these emission lines will change with time as the active regions rotate across the stellar disk. The existence of active regions will tell us unambiguously that the hot plasma is magnetically confined and magnetically heated, rather than heated by acoustic waves. Existing FUSE spectra of Altair show that the OVI and CIII emission lines have a horned appearance, indicating that emission near the limbs can be resolved due to the rapid rotation of the star. We present a new long (36 ksec) FUSE observation of Altair, and explore emission line variability over a stellar rotation period.

A Search for Spectroscopic Binaries Among Very Low-Mass Stars and Brown Dwarfs

Ansgar Reiners (Astronomy Department 521 Campbell Hall Berkeley, CA)
Gibor Basri (Astronomy Department, 651 Campbell Hall, Berkeley, CA)

This project is a search for spectroscopic binaries (SB) among very low-mass stars and brown dwarfs. There is no question that the formation of binary and multiple systems is a common mode of star formation. While the binary frequency for solar-type stars is roughly known, the situation for extreme masses and mass-ratios is very poor. About 20% of the field L dwarfs are double in an HST image; none with separations more than about 10 AU (Bouy et al. AJ 126, 1526, 2003). We will learn whether the separation distribution for low-mass SB is merely compressed, truncated at larger separations, or seriously different than the stellar binary distribution. As a pioneering effort, we are reobserving the more than 60 stars studied by Mohanty & Basri (ApJ 583, 451, 2003) to look for radial velocity variability using the HIRES echelle on Keck. We use the same settings as the original epoch, so that the problem becomes one of just finding the relative shift of the stellar signal with respect to the "rest" indicators. For each of the three references (stellar, telluric, lamps) we cross-correlate using a mask that isolates each. Sensitivity to 300 m/s brings us out to the minimum separations that AO or HST can uncover (the objects are generally less than 20pc distant). Thus far, it appears that the number of SB is not very high, pointing in the direction of a cut-off at wide separations.
http://astron.berkeley.edu/~areiners/

Dynamos with feedback of jxB force on meridional flow and differential rotation

Matthias Rempel (High Altitude Observatory National Center for Atmospheric Research Boulder Colorado USA)
Mausumi Dikpati (National Center for Atmospheric Research)
Keith MacGregor (National Center for Atmospheric Research)

Flux-transport dynamos have been proven to be a very successful approach for modeling the evolution of the large scale solar magnetic field. However, these studies addressed the transport of magnetic field by the meridional circulation in a purely kinematic approach. The toroidal field strength at the base of the solar convection zone inferred from studies of rising magnetic flux tubes is around 100 KG and thus orders of magnitude larger than the equipartition field strength estimated from a meridional flow velocity of a few m/s. Therefore it is crucial for flux-transport dynamos to address the feedback of the jxB on the meridional flow. In this paper we present two approaches: 1) A kinematic approach in which we parameterize this feedback in terms of a non-linear quenching of the meridional flow in regions of strong field. 2) A MHD approach in which we solve the full set of hydrodynamic equations together with the dynamo equations. Since we focus in this approach only on the large scale flow field, the anisotropic turbulent transport of angular momentum responsible for the differential rotation is parameterized. From both studies we conclude that Babcock-Leighton flux-transport dynamos work even with strong feedback of the jxB force for mainly two reasons: 1) The transport of the weak poloidal magnetic field is not affected strongly. 2) The meridional flow results from a small difference between large forces, so that the transport capability is much larger than a simple estimate based on equipartition field strengths suggests.
This work is partially supported by NASA grants W-10107 and W-10175. The National Center for Atmospheric Research is sponsored by the National Science Foundation.

Nearby stars in the Liverpool-Edinburgh high proper motion survey

Céline Reylé (Besançon Observatory)
A.C. Robin (Besançon Observatory)

Recent discoveries of cool objects, such as M stars or brown dwarfs, closer than 5 parsecs show that the solar neighbourhood sample is still not complete. We present a systematic search for new nearby stars in the Liverpool-Edinburgh high proper motion survey which we cross-identified with the DENIS survey. Their high proper motions ensure that they are not giant stars. The distances are estimated using DENIS photometry and we found that 100 stars, mainly M stars, probably lie within 25 parsecs from the Sun, the distance limit of the Catalogue of Nearby Stars. In addition for the closest stars, spectroscopic distances were obtained from observations at the NTT (ESO).

X-ray spectroscopy of M dwarfs

Jan Robrade (Hamburger Sternwarte Gojenbergsweg 112 21029 Hamburg)
J.H.M.M. Schmitt (Hamburger Sternwarte)

We present an analysis of XMM-Newton observations of active M dwarfs with spectral types M3.5 - M4.5. We use X-ray data from four object, the binary systems EQ Pegasi and AT Microscopii as well as the single stars AD Leonis and EV Lacertae. While the main focus is on spectral analysis and the determination of plasma temperatures, abundances and emission measures we also present a light curve analysis and investigate the consistency of the results obtained by the different instruments onboard XMM-Newton. We use multi temperature models with variable abundances to fit the individual spectra and to study the physical changes of the coronal plasma properties during different states of activity. Significant increase in the prominence of the hot plasma component has been observed during flares.
http://www.hs.uni-hamburg.de/DE/Ins/Per/Robrade/index.html

The Tucanae and Horologium Associations: Chemical Abundances

Gustavo Rojas (Instituto de Astronomia, Geofísica e Ciências Atmosféricas Universidade de São Paulo, Brasil)
Jane Gregorio-Hetem (Universidade de São Paulo)

Recently, the Tucanae (TucA) and Horologium (HorA) associations were identified as nearby groups of young stars (Zuckerman & Webb 2000, Torres at al. 2000). The members of these associations have similar space motions and ages, which suggest that they may have been formed from the same parental cloud 40 Myr ago. In the present work, we perform a chemical analysis of 11 TucA and 3 HorA members, aiming to verify if they show a similar pattern of chemical compositions, which would consist in a strong argument for the common origin of both associations. The method for the chemical analysis includes a precise determination of the effective temperatures, using line-depth ratios of iron lines with different excitation potentials, and surface gravities (based on the HR diagram). The chemical abundances were calculated using spectral synthesis and up-to-date stellar atmosphere models.
http://www.astro.iag.usp.br/~rojas

Magnesium emission at 12 micron

Nils Ryde (Department of Astronomy and Space Physics, Uppsala University)
Matt Richter (Department of Physics, University of California at Davis)

We report on stellar magnesium I emission at 12 micron obtained with TEXES, a high-resolution, mid-infrared spectrograph. We will discuss the diagnostic value of these lines.

The Coronal Emission Measure of the Single Giant Beta Ceti

Sarah Saegesser (University of Oxford)
I will present a detailed emission measure analysis of the G9.5 giant Beta Ceti, obtained from line flux measurements from the XMM-Newton instruments RGS1 and RGS2. Relative element abundances and plasma parameters will be discussed. Beta Ceti is a G9.5 giant, located at the base of the red giant branch. Despite its low rotational velocity of 3 km/s, its coronal X-ray emission is very strong. It has been suggested that this star is seen pole-on, but photometric light curve analysis indicates that the star has a rotation period of around 170 days and is therefore indeed a slow rotator. The RGS fluxes of first and second order were measured with CORA, a fitting tool developed by Ness & Wichmann (2002) to pay attention to Poissonian statistics occurring due to low count rates. The results will be compared to the ones obtained from published fluxes of Capella.

The "not-so-MAD" coronal abundances of active stars

Jorge Sanz-Forcada (ESTEC-European Space Agency )
Fabio Favata (ESTEC-European Space Agency)
Giuseppina Micela (Osservatorio Astronomico di Palermo)

Coronal abundances have been a subject of debate in the last years due to the availability of high-quality X-ray spectra of many cool stars. Coronal abundance determinations have generally been compared to solar photospheric abundances; from this a number of general properties have been inferred, such as the presence of a coronal metal depletion with an inverse First Ionization Potential dependence, with a functional form dependent on the activity level. We report a detailed analysis of the coronal abundance of 4 stars with various levels of activity and with accurately known photospheric abundances. The coronal abundance is determined using a line flux analysis and a full determination of the differential emission measure. We show that, when coronal abundances are compared with real photospheric values for the individual stars, the resulting pattern can be very different; some active stars with apparent Metal Abundance Deficiency in the corona have coronal abundances that are actually consistent with their photospheric counterparts.

Doppler imaging with Fisher Information matrix: new perspectives

Igor Savanov (Astrophysical Institute Potsdam, An der Sternwarte, 16 D-14482 Potsdam, Germany)
New benefits of the statistical approach to inverse problems proposed by V.Terebizh (1995,2004) are introduced in our Doppler imaging code. To determine the principal axis of the error ellipsoid in image space we use Singular Value Decomposition of the Fisher information matrix. Rejecting those eigenvectors with small eigenvalues that only added noise the to the solution we perform reconstruction of a stellar surface image. The optimal solution keeps only the minimum number of principal components required for the agreement with the observational data. The criterion for the choice of the extended set of principal components is based on the construction of a nonlinear filter close to the optimal Kolmogorov - Weiner filter.Our Doppler imaging code also made it possible to perform the reconstruction of surface temperature maps using molecular features from TiO, CO, OH, CN etc bands which are numerous in spectra of late type dwarfs. Atomic and molecular features can be used in restoration procedure simultaneously.

Comparison of coronal properties of G-type stars in different evolutionary phases

Luigi Scelsi (Universita' di Palermo Piazza del Parlamento 1, 90134 Palermo, Italy)
Antonio Maggio (INAF - Osservatorio Astronomico di Palermo)
Giovanni Peres (Universita' di Palermo)

We report on the analysis of XMM-Newton observations of three G-type stars in very different evolutionary phases: the ''weak-line'' T Tauri HD 283572, the Zero Age Main Sequence star EK Dra and the Hertzsprung-gap giant star 31 Com. The X-ray luminosity of HD 283572 and 31 Com are about equal (∼ 10³¹ erg/s) and larger than that of EK Dra by an order of magnitude. We compare the Emission Measure Distributions of these bright sources, derived from high-resolution XMM-Newton X-ray spectra, as well as the pattern of elemental abundances vs. FIP. The results of our analysis suggest that the coronae of stars with high L_X may be very similar in terms of dominant coronal magnetic structures, in spite of differences in the evolutionary phases, surface gravities and metallicities.

Magnetic Activity in Early-type Stars ?

Jürgen Schmitt (Hamburger Sternwarte)
D. Groote (Hamburger Sternwarte)
S. Czesla (Hamburger Sternwarte)

Magnetic Activity is traditionally restricted to late-type stars with outer convective envelopes. In these stars dynamo action is thought to lead to magnetic field generation and ensuing activity phenomena. We will present a number of enigmatic X-ray observations of early-type stars with strong magnetic fields and X-ray detections. While traditionally low-mass companions are held responsible for the observed X-ray emission, we argue that a more plausible explanation for the observed emission properties is an association with the early-type non-convective star.

The T Tauri phase of Brown Dwarfs

Alexander Scholz (Thueringer Landessternwarte Tautenburg)
Jochen Eisloeffel (Thueringer Landessternwarte Tautenburg)

The origin of Brown Dwarfs (BDs) is still subject of debate. By a detailed study of circumsubstellar disks, it is in principle possible to decide between the competing formation scenarios. From recent studies, it is obvious that young BDs possess accretion disks. The investigation of their accretion properties, however, is still in its infancies. Here, we report about our ongoing efforts to identify and study accreting BDs and very low mass (VLM) stars. The accretion process shows up as high variability in photometric lightcurves and strong emission features in optical spectra, while the disk manifests itself through a NIR colour excess. Particularly their variability is very similar to those of classical T Tauri stars, with strong irregular variations often combined with a periodic component. Thus, it is apparent that we observe the T Tauri stage in the evolution of BDs. These studies have also the potential to clarify one important aspect of the rotational evolution of BDs, since the disk plays a major role in the rotational braking process. The observed fast rotation of VLM objects could be explained by a change in the physics of the accretion disk.
http://www.tls-tautenburg.de/research/scholz/index.html

The Stellar Imager: a deep-space telescope to image stellar surfaces.

Carolus J. Schrijver (Lockheed Martin Advanced Tech. Ctr. Palo Alto, California)
Kenneth G. Carpenter (NASA Goddard Space Flight Center, Goddard, Maryland)
Margarita Karovska (Smithsonian Astrophysical Observatory, Cambridge, Massachusetts)

The Stellar Imager (SI) is a "Vision" mission in NASA's Sun-Earth Connection (SEC) Roadmap, conceived for the purpose of understanding the effects of stellar magnetic fields, the dynamos that generate them, and the internal structure and dynamics of the stars in which they exist. The ultimate goal is to achieve the best possible forecasting of solar/stellar magnetic activity and its impact on life in the Universe by the study of the internal structure and flows of stars and of the dynamo patterns that they sustain. The science goals of SI require an ultra-high angular resolution, at ultraviolet wavelengths, on the order of 100 micro-arcsec and thus baselines on the order of 0.5 km. These requirements call for a large, multi-spacecraft interferometer. SI's resolution will make it an invaluable resource for many other areas of astrophysics, including young stars and star-forming systems, AGNs, supernovae, cataclysmic variables, QSOs, and stellar black holes. We present an overview of the mission's science, concept design, and technology development. Additional information on SI mission concepts and technology can be found at URL: http://hires.gsfc.nasa.gov/ si .
http://hires.gsfc.nasa.gov/~si

A new semi-empirical mass-loss relation for all cool winds not driven by dust

Klaus-Peter Schroeder (Astronomy Centre, University of Sussex, Falmer, Brighton BN19QH, UK)
We present a new semi-empirical model for the mass-loss from cool winds not driven by dust, so far have been described by the Reimers relation. The wind is treated as a spill-over of the extended and very turbulent giant chromospheres. Consequently, the mechanical power input should be proportional to the (basal) chromospheric emission line luminosity L_Chr, and the potential energy input required to lift the wind material is counted from a characteristic chromospheric height R_Chr. For the latter, we use the sonic point of the average velocity field (known for the well studied K supergiant ζ Aur), assuming its height to vary with g_*^-1. Since observations also suggest basal chromospheric flux F_Chr,bsl ∝ T_eff^7.5, we find M = η ⋅ L_* R_*/M_* ⋅ (T_eff/4000K)^3.5 ⋅ (1+g_ˆ/4300 ⋅ g_*). The new relation makes a significant difference for the luminous AGB (and post-AGB) stars. Here, R_Chr boosts the mass-loss, in good agreement with observation.

X-ray emission from A-type stars

Christian Schroeder (Hamburger Sternwarte Gojenbergsweg 112 21029 Hamburg)
J.H.M.M. Schmitt (Hamburger Sternwarte)

Being fully radiative, stars of spectral type A are not expected to harbor magnetic dynamos and hence such stars are not expected to produce X-ray emission. Indeed, while the X-ray detection rate of such stars in X-ray surveys is low, it is not zero and some of the brighter A-type stars have been detected on different occasions and with different instruments. In order to systematically study the puzzle of the X-ray emitting A-type stars, we performed an X-ray study of all A-type stars listed in the Bright Star Catalogue using the ROSAT public data archive. We found a total of 300 bright A-type stars positionally associated with ROSAT X-ray sources; we analysed the X-ray light curves as well as searched for evidence of RV variations to identify possible late-type companions producing the X-ray emission. We present a list of "bona fide" A-type stars, which are secure X-ray sources without any evidence (so far) of hidden companions.

AGB stars in the galactic Bulge: new insights on pulsation and mass-loss

Mathias Schultheis (Observatoire de Besancon)
A. Omont (Institute d'Astrophysique de Paris)
I.S. Glass (SAAO, Capetown, Southafrica)

During the last years, taking advantage of the microlensing surveys such as MACHO together with the near-IR surveys of 2MASS, new insights on the pulsation of AGB stars came out. I discuss the period-luminosity relations of the different type of AGB stars such as Mira variables and semiregular variables and compare them with different galactic environments (with different metallicity) such as the LMC and SMC. Coupling this pulsation with data of ISOCAM at 7 and 15 micron, enables us for the first time to trace mass-loss in the central parts of our Galaxy. We see clearly that the mass-loss starts around a period of ≈ 100 days,an important parameter for the models of dust formation of AGB stars.I discuss further on the dependence of pulsation and mass-loss as a function of metallicity.
Using the powerful tool of infrared spectroscopy together with IR photometry between 2.2 and 15 micron, I discuss the nature of AGB stars in the highest obscured regions in our Galaxy, close to the galactic center, where we deal with extinction in the order of 30 magnitudes.AGB stars are an excellent tracer of galactic structure. I summarize the most important results such as mass-loss and metallicity studies of the AGB star population.
http://www.obs-besancon.fr/publi/MathiasSchultheis/Mathias.html

High Resolution X-ray Spectroscopy of Very Young Stars

Norbert S. Schulz (Massachusetts Institute of Technology)
Dave P. Huenemoerder (Massachusetts Institute of Technology)
Claude R. Canizares (Massachusetts Institute of Technology)

Many highly resolved X-ray spectra of very young stars have become available through recent years and their analysis so far revealed a rather broad palette of plasma emissions. Specifically surprising was the finding that the X-ray spectra of very young hot stars exhibit decisive fingerprints that make them look more like "cool" stars. The study of high energy signatures from very young massive stars has always been difficult due to the short time scales involved in their evolution. The time between collapse, full hydrogen burning and disk dispersal in massive stars is of the order of 10⁵ yr, in contrast to a few 10⁶ yr for T Tauri stars. The high spatial and spectral resolution of Chandra made it possible to resolve the cores of very young open clusters in X-ray wavelengths. One of the intriguing results from these Chandra observations is that most young early type stars possess hot, corona-like spectral signatures, some do not. Likely more evolved stars, for example in cores of clusters older than 3 Myr as in Tr 37 in IC 1396 or NGC 2362, behave more like the prototype O-starζ Pup. We provide new insights from high resolution X-ray spectroscopy of massive stars at possibly various evolutionary stages and compare them to spectral signatures of T Tauri stars as well as stars with active coronae.

X-ray spectral and timing properties of the IC 2391 stars

Salvatore Sciortino (INAF - Oss. Astronomico di Palermo Giuseppe S. Vaiana, )
A. Marino, G. Micela (INAF - Oss. Astronomico di Palermo Giuseppe S. Vaiana)
G. Peres (DISF&A, Universita` di Palermo)

We present X-ray spectral and timing analysis of late-type members of the young open cluster IC 2391 observed with XMM-Newton/EPIC instrument.
The X-ray spectral analysis of the X-ray brightest cluster stars shows that a spectral model with two thermal components (at kT₁ ≈ 0.3-0.5 keV and kT₂ ≈ 1.0-1.2 keV respectively) describes well the coronal spectra of K and M stars, while for F stars a softer 1-T model is appropriate.
The Kolmogorov-Smirnov test applied to the X-ray photon time series shows that approximately 50% of the IC 2391 members are variable at a confidence level > 99%. The comparison of our data with those obtained with ROSAT/PSPC, nine years earlier, and ROSAT/HRI, seven years earlier, shows that there is no evidence of significant variability on these time scales.

Doppler imaging of Sigma Gem and HR1099

Alina Semenova (Max-Plank Institut für Aeronomie)
Svetlana Berdyugina (Institute of Astronomy, ETH Zentrum, Zurich)
Sami Solanki (Max-Plank Institut für Aeronomie)

In contrast to the Sun, other stars remain point sources even in observations with the best telescopes. Doppler imaging is a valuable tool for making stellar surfaces 'visible'. Using this technique, we reconstruct surface maps of two stars. Spectra of Sigma Gem were obtained with a CCD camera on the Nordic Optical Telescope in La Palma during 19 nights in the period between 07.11.2000 and 15.12.2000. This allowed us to compose a set of observations covering one full rotational period. For the analysis we chose a spectral region with four atomic lines (Fe I 6173.33 A, Ni I 6175.36 A, Ni I 6172.23 A and Fe I 6180.2 A). New observations of the star HR1099 are now being carried out at the Thueringen Observatory. For reconstruction of stellar surface of this star, molecular lines (TiO-band) are used in addition to the usual atomic Doppler Imaging lines. For HR1099 preliminary results are presented. The images were made by using the code of Berdyugina (1998) based on the Occamian approach.

Lithium evolution and mixing mechanisms in open clusters

Paola Sestito (Dipartimento di Astronomia, Universita' di Firenze)
Sofia Randich (INAF/Osservatorio Astrofisico di Arcetri)

Lithium is a very good tracer of mixing processes occurring in stellar interiors, due to its relatively low burning temperature. Open clusters (OCs) represent a natural testing ground for investigating Li depletion as a function of age/mass/chemical composition. Studies of Li in OCs reveal several discrepancies between empirical evidence and theoretical predictions. Furthermore, the current observational scenario is likely to be affected by uncertainties due to different methods of analysis, and a complete picture of Li evolution in the age-mass-metallicity plane is not yet available. We report here a new homogeneous analysis of all the Li data for G and early-K stars in OCs of different ages and metallicities available in the literature: in this way, we have provided a completely unbiased database, putting all the clusters on the same scale of Li abundances and effective temperatures. Based on this revised set of abundances, we discuss the time scales of Li depletion in different age intervals and the dependence on metallicity.

Chromospheric activity of red giants

Johny Setiawan (Max-Planck-Institut für Astronomie, Heidelberg, Germany)
O. von der Lühe (Kiepenheuer-Institut für Sonnenphysik, Freiburg)
L. Pasquini (European Southern Observatory, Garching)

We present results of our spectroscopic survey of red giant stars carried out between 1999 and 2003. We found clear evidence for chromospheric activity variation in the spectra of least eight G and K giants: HD 7672, HD 50778, HD 62644, HD 78647, HD 81797, HD 110014, HD 107446 and HD 151249. The origin of variations in the chromospheric activity of these stars may be due to giant starspots and stellar wind in binary systems. We applied the cross-correlation method to measure the stellar radial velocity with a precision of some 25 m/s and the asymmetry of the spectral line profile using the bisector velocity span. We used the Ca II K emission line in 393.4 nm as chromospheric activity indicator and investigated the TiO-band in 705.5 nm for the presence of giant cool spots.

Fencing the Brown Dwarf desert : a L0 dwarf within 31AU of a M3 dwarf nearby star

Damien Ségransan (Observatoire de Genève 51 ch. des Maillettes, CH-1290 Sauverny, Switzerland)
Thierry Forveille (LAOG and CFHT)
Xavier Delfosse (LAOG )

We present the discovery of a L0 companion to a nearby M3 dwarf in orbit at a distance of 31AU. This L0 dwarf was first identified as a faint potential companion (DeltaJ=4.20) to its parent star using the CFHT adaptive optics in 2001. It was confirmed one year later as a gravitationally bound companion thanks to their common proper motion. With an absolute magnitude of M_J=11.30-11.45 and a color of J-K=1.20-1.30, this cool companion was identified as a L1 ± 2. Its accurate spectral type was recently determined using the WHT near infrared spectrograph LIRIS with a resolution of R ≈ 700 between 1-2.4 µ m.
http://obswww.unige.ch/~segransa/

The mass-radius relation : from low mass stars to planets

Damien Ségransan (Observatoire de Genève 51 ch. des Maillettes CH-1290 Sauverny, Switzerland)
Pierre Kervella (Observatoire de Paris Meudon)
Thierry Forveille (Laboratoire d'Astrophysique de Grenoble - CFHT)

We present the measurement of 5 low mass stars radii observed at the VLTI using the 2.2 mu m VINCI test instrument. We measure angular diameters of 1.2-6. mas with accuracies of a few percent for spectral type ranging from K1V to K4.5V. We extend the already published empirical mass-radius relation for M dwarfs to the K dwarfs domain as well as to the planet domain thanks to the recent measurement of the radii of transiting hot jupiters. Stellar and planet interior and evolutionary models are now strongly constrained by such measurements.
http://obswww.unige.ch/~segransa/

NLTE models of extremely metal poor stars

Ian Short (Department of Astronomy and Physics and Institute for Computational Astrophysics Saint Mary's University)
Peter Hauschildt ()

We present atmospheric models and synthetic spectra for red giant stars of -5<[A/H]<0 with spherical geometry and tens of thousands of atomic and ionic transitions, including those of the Fe group elements, in self-consistent NLTE using the PHOENIX code. We pay special attention to how well-known NLTE effects vary with metallicity down to XMP values. Preliminary results indicate that the shape of the overall flux distribution is only marginally affected by NLTE at extremely low metallicities, but that the strengths of many individual lines are significantly affected. Generally, we quantify the suspicion that LTE abundance analyses of XMP stars may be subject to significant revision for some elements.

Rotational velocity for metal-poor evolved stars

Jose Ronaldo P. Silva (Departamento de Física / UERN)
Jose D. do Nascimento (Departamento de Física / UFRN)
Jose R. De Medeiros (Departamento de Física / UFRN)

On the basis of a high resolution spectroscopic survey, carried out with the FEROS spectrometer, we present projected rotational velocity for a large sample of about 90 metal--poor evolved stars. The rotational velocities, analyzed as a function of effective temperature and mass, present some very interesting features, in particular an apparent excess of low rotators at the AGB and a discontinuity at the BHB.

Magnetic field of T Tau

Daniil Smirnov (Sternberg Astronomical Institute)
Sergey Lamzin (Sternberg Astronomical Institute)
Marina Romanova (Department of Astronomy, Cornell University)

We present results of our measurements of longitudinal magnetic field of T Tau, obtained during three sets of spectropolarimetric observations. Using photospheric lines we found B_||≃ 150± 50 G in 1996, 2002 and B_||≃ 15± 30 G in 2003, what means that B_|| value is variable in the photosphere of T Tau. In addition we measured B_|| in the He I 5876 emission line formation region, i.e. in the magnetosphere of the star and found B_|| ≃ +650, +350 and +1100 January 16, 18 and February, 15 2003 respectively. Our observations January 18 and February 15 correspond to virtually the same phase of the star rotation period, but the profiles of the He I 5876 line differ markedly on these two nights. Therefore, we belive that the threefold difference between the B_|| values on these nights does not result from observational errors.
Our estimations of photospheric B_|| are more than one order of magnitude less surface field (B>2 kG), found by Guenther et al. (1999) and Johns-Krull et al. (2000). Possible reasons of this difference and restrictions on T Tau`s field geometry are discussed.

Simultaneous radio and X-ray observations of flares in late-type stars.

Kester Smith (MPIfR Bonn Germany)
Manuel Guedel (PSI, Switzerland)
Marc Audard (Columbia, New York)

We present simultaneous light curves taken in radio with the VLA and in X-rays with XMM-Newton for several flare stars. Correlations between the activity in each band - such as the Neupert effect - indicate causal connections between the emission mechanisms. In some cases where there is no correlation, this correlation between the different bands also yields information about the probable emission mechanisms. In cases where the X-ray and radio activity is correlated, we use an energy budget argument to show that the accelerated particles giving rise to the radio emission can also be responsible for the heating which leads to the X-ray emission.

Spot the differences - the X-ray spectrum of SU Aur compared to TW Hya

Kester Smith (MPIfR Bonn Germany)
Marc Audard, Manuel Guedel (Columbia NY, PSI Switzerland )
Steve Skinner, Roberto Pallavicini (CASA Colorado, Palermo Observatory)

We present high-resolution Chandra HETGS X-ray spectra of the classical T Tauri star SU Aur. The quiescent X-ray emission is dominated by a 20--40MK plasma, which contrasts strongly with the cool 3MK plasma dominating the X-ray emission of the CTTS TW Hya. In addition, a large flare occurred during the first half of our 100ks observation, and we have modelled the emitting plasma both during this flare and during the apparently quiescent periods. During the flare, an extremely high temperature plasma component (at least 60MK) accounts for the bulk of the emission. There is an indication of the presence of Fe XXVI emission at 1.79 Angstrom, which is maximally formed at 130 MK. We discuss plasma emission measure distributions, abundances and absorption in the context of expected conditions pertaining to classical T Tauri stars.

THIS High resolution mid-IR remote sensing by heterodyning with Quantum-Cascade Lasers

Manuela Sornig (1.Physikalisches Institut der Universität zu Köln Zülpicher Straße 77 50937 Köln)
Volker Vetterle (1.Physikalisches Institut der Universität zu Köln)
Daniel Wirtz (1.Physikalisches Institut der Universität zu Köln)

We report on the latest results gained with the Cologne Tuneable Heterodyne Infrared Spectrometer THIS. The instrument incorporates Quantum-Cascade Lasers as local oscillators and is designed for high resolution (R=107) remote observations in the mid-IR region (λ = 8-28 µ m).
Scientific goals are for example studies of composition and dynamics of planetary atmospheres. THIS was successfully operated on the McMath-Pierce Solar Telescope at Kitt Peak / Arizona to observe Ozone absorptions in the martian atmosphere as well as natural non-LTE CO2 emission on Mars and Venus.
It was also shown that it is possible to detect stratospheric ozone against pointsources (like the red giant star Betelgeuse) as a background. This opens the door to the detection of molecular features in the 10 micron ``Fingerprint''-region in stellar atmospheres and the interstellar medium. Especially cold gas, exhibiting narrow lines are a promising target for THIS. Possible sources are for example IRC+10216 or CRL618.
Future observations with THIS could address the distribution of molecular Hydrogen in the cold interstellar medium. Provided suitable lasers and detectors, especially the two lowest lying pure rotational transitions at 17 and 28 are of special interest.
Due to its compact design and independent guide-optics THIS can be operated at almost all kinds of earthbound telescopes and is proposed for the second flight period aboard the Stratospheric Observatory for Infrared Astronomy SOFIA in the future.
THIS provides a maximum resolution of 1,4 MHz (corresponding to 14 m/s at 10 ) and a bandwidth of currently 1.4 GHz which instantaneously analysed using an in house built Acousto-Optical Spectrometer. The instrument operates close to the Quantum Limit and is thus equivalent to established CO2-Laser driven receivers. These features combined with the highly integrated, transportable and flexible setup results in a unique tool for astronomical observations in the mid-IR.
http://www.ph1.uni-koeln.de/workgroups/astro_instrumentation/this/

A spectroscopic study of Algol systems

Faruk Soydugan (Ege University, Observatory Bornova 35100, Izmir, TURKEY)
Antonio Frasca (INAF - Osservatorio Astrofisico di Catania, via S. Sofia, 78, I-95123 Catania, ITALY)
Santo Catalano (INAF - Osservatorio Astrofisico di Catania, via S. Sofia, 78, I-95123 Catania, ITALY)

We present and discuss here new high-resolution (R= 22000) optical spectra of three Algol binaries, namely KO Aql, S Equ and AT Peg, obtained with the echelle spectrograph of Catania Astrophysical Observatory.
We obtained new radial velocity curves for the hotter primary components with a much better precision than previous data in the literature, mainly coming from old plate spectra. Thanks to the cross-correlation procedure, we were also able to obtain, for the first time to our knowledge, radial velocities also for the cool secondary components of these three systems. This allows us to perform more accurate orbital solutions and mass determination.
We have also measured, with a rather good accuracy (2-4 km/s), the rotational velocity of the hotter components of these three systems and found that, with the exception of AT Peg, the primary stars are rotating faster than the synchronized velocity, consistently with a mass transfer scenario.
We also present preliminary results of the application of a spectral synthesis method to study the effects of mass transfer displayed by the H-alpha extra-emission/absorption components.
http://astronomy.sci.ege.edu.tr/~euobs/EN/indexen.html

High resolution spectroscopic study of red clump stars in the Galaxy: main atmospheric parameters

Egidijus Stasiukaitis (Vilnius University Institute of Theoretical Physics and Astronomy Gostauto 12, Vilnius, Lithuania)
G. Tautvaisiene, E. Stasiukaitis, E. Puzeras, D.F. Gray, I.Ilyin ()

Observations by Hipparcos satellite demonstrated that a population of helium-core-burning stars is a prominent feature of the color-magnitude diagram of stars in the solar neighborhood. However this class of evolved stars is barely investigated by means of high-resolution spectroscopy. This is because their atmospheric parameters are similar to those of ordinary giants and for many years it was difficult to identify them in the Galactic field. We obtained high-resolution and high signal-to-noise ratio spectra of 51 red clump stars selected from the Hipparcos Catalogue. In our contribution we present the results of atmospheric parameter and metallicity determinations. A homogeneity of the sample of stars investigated is discussed.

3D Simulation of Surface Convection and Spectral Line Formation in A-type Stars

Matthias Steffen (Astrophysikalisches Institut Potsdam)
Bernd Freytag (GRAAL, Université de Montpellier II)

We present new numerical simulations of 3D radiative convection in the surface layers of main sequence A-Type stars with effective temperatures around 8000K, recently performed with the CO5BOLD radiation hydrodynamics code. The physics includes a realistic equation of state with ionization, and 3D non-local radiation transport using Phoenix-OPAL opacities. The resulting models are used to investigate the structure of the H+HeI and the HeII convection zones and their interaction, and to determine the amount of `overshoot' from the convection zones into the adjacent stable layers. Such models are suitable to serve as a reference for testing local and non-local convection theories. The simulations also predict how the topology of the photospheric granulation pattern changes from solar to A-star convection. The influence of the corresponding photospheric temperature and velocity fields on the shape of spectral lines is demonstrated by computing synthetic line profiles and bisectors for some representative examples, allowing us to confront the model results with observation.

Spectro-Astrometry with UVES: Towards sub-milli arcsec resolution

Michael Sterzik (ESO/Chile)
A. Tokovinin (CTIO)
C. Melo, C. Hummel (ESO/Chile)

We will present an analysis of the potential of differential spectroastrometry using the long-slit mode of ESO's high-resolution optical spectrograph UVES. The spectroastrometric technique has been proposed by Beckers (1982) and enables to study spatial scales much smaller than set by the natural seeing by measuring the positional displacement across a line profile in high signal-to-noise spectra. We use archival data of high-resolution spectra of nearby stars observed during the "UVES Paranal Observatory Project" to demonstrate the performance and limitations of this technique. The application of this technique to measure stellar rotation axis and relative orbit orientations in multiple systems has far-reaching implications on contending star formation theories.
http://www.sc.eso.org/~msterzik

First results from the FLAMINGOS survey of GMCs: The Monoceros Cloud

Andrea Stolte (Department of Astronomy University of Florida)
Elizabeth A. Lada (Department of Astronomy, UFL)
Joanna Levine (Department of Astronomy, UFL)

The University of Florida FLAMINGOS survey covers five giant molecular clouds and several intense star-forming regions with deep, wide-field JHK imaging. Multi-object spectroscopy of subsamples of the stellar populations forms the basis for age dating and spectral classification, with the goal to obtain the low-mass IMF. The spatial distribution of low-mass stars and brown dwarfs is studied with respect to the star formation environment, and the existence of circumstellar disks is deduced from NIR excesses. Here, we will show the first results from the FLAMINGOS survey for the distribution of low-mass stars in the Monoceros giant molecular cloud and its central cluster NGC 2264.

The STELLA Robotic Observatory. I. Two new 1.2m Telescopes for Tenerife

Klaus G. Strassmeier (Astrophysical Institute Potsdam (AIP))
Thomas Granzer (AIP)
Michael Weber (AIP)

STELLA is a robotic observatory with two fully automatic 1.2m telescopes (STELLA-I and STELLA-II) located at the Teide Observatory in Tenerife, Spain. Not only the telescopes are automatic but also the entire observatory, no human presence is needed for observing - not even in remote control. STELLA-I supports a high-resolution, fiber-fed and bench-mounted echelle spectrograph while STELLA-II feeds a wide-field CCD imaging photometer.
www.aip.de

The STELLA Robotic Observatory. II. Overview of its Scientific Instrumentation

Klaus G. Strassmeier (Astrophysical Institute Potsdam (AIP))
Manfred Woche (AIP)
Michael Andersen (AIP)

The STELLA-I telescope fiber feeds a bench mounted, high-resolution echelle spectrograph (SES) through its single Nasmyth focus. The wavelength range for a single exposure is 390-860nm at a resolution of R=50,000. The STELLA-II telescope is principally an advanced copy of STELLA-I and is designed for automatic use of both Nasmyth foci. The first focus has an image derotator which will be equipped with a wide-field imaging photometer (WIFSIP) based on a large-format high-QE CCD. The second focus will be used for testing a low-cost adaptive optics system for later implementation of a near-IR instrument.
www.aip.de

Hydrodynamical simulations of convection related stellar micro-variability

Fredrik Svensson (Lund Observatory Box 43 S-22100 Lund Sweden)
Hans-Günter Ludwig (Lund Observatory, Box 43, S-22100 Lund, Sweden)

The presence of granular flows on the surfaces of late-type stars poses ultimate limits to the photometric stability, the stability of the photo-centric position, and the stability of the spectroscopically derived radial velocities. Characterizing these limits has bearings on high precision satellite experiments in the fields of planet and p-mode searches, as well as astrometry (e.g. MOST, KEPLER, GAIA). We use a series of CO5BOLD hydrodynamical convection models covering stellar objects from white dwarfs to red giants to derive estimates of the photometric and photo-centric stellar variability across the Hertzsprung-Russell diagram. We validated our models against solar measurements from the SOHO/VIRGO instrument. As a first result of the ongoing investigation we found that stellar astrometry at the precision level of GAIA will only be little affected by granulation related fluctuations - with the exception of close by supergiants.

Spectra and Colors of L, M, and T Dwarfs in the L-M Band Region - Their Role in Testing Cloudy Model Photospheres

Takashi TSUJI (Institute of Astronomy The University of TokyoMitaka, Tokyo, 181-0015 Japan )
So far, the near infrared region (J, H, and K band regions) of the spectra of ultracool dwarfs are relatively well explored, and the results are reasonably well accounted for with the cloudy model photospheres (e.g. our unified cloudy model - UCM). Recently, observations are being extended to an observationally more difficult region such as the L-M band region (2.5 - 5.0 micron: e.g. Golimowski et al. astro- ph/0402475), and the results should be used for further assessment of the models of ultracool dwarfs. For example, we show that the characteristic features of the L' and M' colors can be predicted with our UCMs as well, and thus the SEDs covering the J,H,K,L,and M regions can be consistent with our models. Spectroscopic data are still meager, but we show that the strength of the Q branch of the CH4 3.3 micron bands, for example, is an excellent probe of the dust column density in the cloud. Also, the role of gaseous molecules can be better studied under the decreased dust extinction in the L-M region, and one interesting problem is the non- equilibrium CO bands detected at 4.6 micron in GL229B. We examine this problem in some detail with our UCMs.
http//www.mtk.ioa.s.u-tokyo.ac.jp/~ttsuji

Coronal Evolution of Solar Analogs: A Study with XMM-Newton

Alessandra Telleschi (Paul Scherrer Institute PSI CH-5232 Villigen)
Manuel Guedel, Kevin Briggs; Marc Audard (PSI; Columbia Univ.)
Steve Skinner; Jan-Uwe Ness (Univ. of Colorado; Hamburger Sternwarte)

We present results from an X-ray spectroscopic study of solar analogs at different ages. All targets are proxies of the Sun that essentially differ only in their rotation periods (and therefore, age) and hence in the efficiency of the magnetic dynamo. High-resolution spectra obtained with XMM-Newton were studied to derive the coronal elemental composition and the thermal stratification. Clear evolutionary changes are seen in the emission measure distributions (EMD), with near-Zero Age Main-Sequence coronae being dominated by steeply rising EMDs revealing plasma up to 20-30 MK. This hot component disappears entirely at ages beyond several hundred Myr when a relatively shallow and cool EMD prevails. We find a concurrent change in the elemental composition, from an "inverse FIP" effect or a relatively flat distribution in the very young examples to a marked low-FIP element enhancement in the older stars. The light curves reveal signs of continued variability, suggesting important contributions of flares to the coronal structure.

The Density of Coronal Plasma in Active Stellar Coronae

Paola Testa (Universita' di Palermo)
Jeremy J. Drake (Harvard-Smithsonian CfA)
Giovanni Peres (Universita' di Palermo)

We have analyzed high-resolution X-ray spectra of 22 active stars observed with the HETGS on Chandra, in order to investigate their coronal plasma density, using the lines of the He-like ions OVII, MgXI, and SiXIII. While SiXIII lines in all stars of the sample are compatible with the low-density limit, MgXI lines betray the presence of high plasma densities (> 10¹² cm^-3) for most of the sources with higher X-ray luminosity (> 10³⁰ erg/s). Ratios of OVII lines yield much lower densities of a few 10¹⁰ cm^-3, indicating that the ``hot'' and ``cool'' plasma resides in physically different structures. Our findings imply remarkably compact coronal structures, especially for the hotter plasma emitting the MgXI lines characterized by coronal surface filling factor, f_MgXI, ranging from 10^-4 to 10^-1, while we find f_OVII values from a few 10^-3 up to ∼ 1 for the cooler plasma emitting the OVII lines. We find that f_OVII approaches unity at the same stellar surface X-ray flux level as solar active regions, suggesting that these stars become completely covered by active regions. At the same surface flux level, f_MgXI is seen to increase more sharply with increasing surface flux. These results appear to support earlier suggestions that hot 10⁷ K plasma in active coronae arises from flaring activity, and that this flaring activity increases markedly once the stellar surface becomes covered with active regions.

Chandra Orion Ultra-deep Project: A Search for 6.4 keV Iron Fluorescent Line from Young Stellar Objects

Masahiro Tsujimoto (Pennsylvania State University)
Eric D. Feigelson (Pennsylvania State University)

In the Chandra Orion Ultra-deep Project (PI: Eric D. Feigelson at Pennsylvania State University), we conducted a 13-day consecutive X-ray observation of a 17x17 arcmin region in the Orion Nebula Cluster for ≈850 ksec with ACIS onboard Chandra. Using the ACIS Extract package developed for a coherent reduction of ACIS data, we produced the largest X-ray database consisting of ≈1600 X-ray sources with photometry and spectroscopy information, and counterparts in other wavelengths (ref. oral presentation by Feigelson).
Using the data, we searched for 6.4 keV iron fluorescent lines from YSOs. Fluorescent lines provide us with a unique diagnosis of cold material around X-ray-emitting plasma, and are widely used in X-ray binaries and AGNs. A 6.4 keV line was first reported in a YSO in the rho Oph. cloud using Chandra (Imanishi et al. 2001, ApJ, 557, 747). We enriched the number of samples with ≈10 new detections and constructed a statistically meaningful dataset of this emission. We discuss the averaged emission features as well as what causes the reflection.
http://www.astro.psu.edu/users/tsujimot

Formation constraints from short-period extra-solar planets?

Stephane Udry (Geneva Observatory)
In about 1 year the sample of known "Hot Jupiters" has increased by 35%, with candidates from the Coralie and HARPS planet-search programmes and from radial-velocity confirmations of the OGLE planetary photometric-transit detections. We will discuss the impact of these new discoveries on the statistical distributions of planetary and parent star parameters and the related implications for planet formation and migration.
http://obswww.unige.ch/Exoplanets

Steps towards a theoretical chromosphere model of the Sun.

Peter Ulmschneider (Institut for Theoretical Astrophysics, Univ. Heidelberg)
The solar chromosphere is a phenomenon which is completely determined by the conditions of the solar interior. Therefore like the solar interior and photosphere, the chromosphere should depend only on a few parameters such as effective temperature, surface gravity, metallicity and rotation rate. I summarize the difficult task to construct theoretical chromosphere models. The theoretical obstacles originate from the time-dependent radiation-hydrodynamics of the solar surface layers, the departures from LTE, the spacial distribution and intermittency of the mechanical heating sources as well as the complicated effects due to the magnetic fields. New calculations towards a realistic solar chromosphere model are presented.

Carbon stars in local group dwarf galaxies: C & O abundances

Rurik Wahlin (Department of Astronomy and Space Physics Uppsala University)
Eriksson, K. (Department of Astronomy and Space Physics Uppsala University)
Gustafsson, B. (Department of Astronomy and Space Physics Uppsala University)

We will present preliminary abundances of carbon and oxygen as well as abundance ratios 12C/13C for a sample of carbon stars in the LMC, SMC, Carina, Sculptor and Fornax dwarf galaxies.
The overall metallicities in these dwarf galaxies are lower than in the galactic disc. The determined abundances can then be used to put constraints on stellar evolution models at different metallicities.
The observed stars cover a large part of the AGB in the HR diagram and we discuss the abundance patterns as functions of initial metallicity and location along the AGB.
The abundances are determined from infrared spectra obtained with the ISAAC spectrometer on VLT (R=1500) and the Phoenix Spectrometer on Gemini South (R=50000)The synthetic spectra used in the analysis are computed with the MARCS model atmosphere code.

The Highly Variable Mass Accretion in S CrA

Frederick Walter (Stony Brook University)
Jesse Miner (Stony Brook University)

Observations in the 1970s and 1980s showed that the classical T Tauri star S CrA often exhibited inverse-P Cygni line profiles, indicative of mass accretion, in the upper Balmer lines. We have revisited this system, taking advantage of the monitoring capabilities of the SMARTS facilities, to compile a long-term spectrophotometric record of the brightness and line profile variations in this star. S CrA is a 1.3 arcsec visual pair, with up to 2 magnitude variations in optical brightness. Although generally dismissed as insignificant, our imaging shows that the SE component is often brighter and bluer than the NW component. We have obtained low dispersion spectra with a cadence of up to 2 spectra per night over the past year. These spectra reveal the timescales of the discrete accretion events. Spectra of the H-alpha line show a time-variable wind at a constant velocity. Our spectroscopy does not resolve the system. We will present the time-series spectra and images, and will report on our attempts to correlate the mass infall, the mass outflow, and the line and continuum brightness variations. The rapidity of the variations in this system present an opportunity to examine the interplay of accretion and atmospheric heating in an accreting T Tauri star.
http://www.astro.sunysb.edu/fwalter

Evolution of stellar active regions

Michael Weber (Astrophysikalisches Institut Potsdam)
Klaus G. Strassmeier (Astrophysikalisches Institut Potsdam)

Results from time series Doppler imaging of K-type giant stars are presented. The evolution of the reconstructed star spots over a period of 70 days, which is on the order of several rotation periods for these stars, is compared with a solar-type differential rotation law. The resulting magnitude of the differential rotation parameter α (if applicable) and its sign is put into relation with physical parameters of the stars like rotational period. Possibilities of comparing these results with theoretical models are explored.
http://www.aip.de/groups/activity/

Science with the STELLA robotic observatory

Michael Weber (Astrophysikalisches Institut Potsdam)
K. G. Strassmeier (Astrophysikalisches Institut Potsdam)
A. Schwope (Astrophysikalisches Institut Potsdam)

The STELLA robotic observatory is made up of two 1.2m telescopes, one equipped with a wide-field imager, the other one equipped with a high resolution echelle spectrograph. The observatory is fully robotic, and its strengths are in long-term monitoring and survey programs on one side, and in observing targets of opportunity on the other side. We present examples of programs planned for routine observation starting next year. From Doppler tomography to medium deep variability surveys, from Gamma ray bursts to accompanying of space observations.
http://www.aip.de/stella

The shock-patterned solar chromosphere in the light of ALMA

Sven Wedemeyer-Böhm (Kiepenheuer-Institut für Sonnenphysik, Freiburg )
Hans-Günter Ludwig / Matthias Steffen (Lund Observatory, Lund, Sweden / Astrophysikal. Institut Potsdam, Potsdam)
Bernd Freytag / Hartmut Holweger (GRAAL, Université de Montpellier II, Montpellier, France / Inst.f.Theo.Phys.u.Astrophys., Universität Kiel)

Recent three-dimensional radiation hydrodynamic simulations by Wedemeyer et al. (2004) suggest that the solar chromosphere is highly structured in space and time on scales of only 1000 km and 20-30 sec, resp.. The resulting pattern consists of a network of hot gas and enclosed cool regions which are due to the propagation and interaction of shock fronts. In contrast to many other diagnostics, the radio continuum at millimetre wavelengths is formed in LTE, and provides a rather direct measure of the thermal structure. It thus facilitates the comparison between numerical model and observation. While the involved time and length scales are not accessible with todays equipment for that wavelength range, the next generation of instruments, such as the Atacama Large Millimetre Array (ALMA), will provide the required resolution. Here we present results of radiative transfer calculations at mm and sub-mm wavelengths with emphasis on the scaling of observables with spatial and temporal resolution which are crucial for the ongoing discussion about the chromospheric temperature structure.
http://www.kis.uni-freiburg.de/~sven

2D dynamical models for dust-driven winds of AGB stars

Peter Woitke (Sterrewacht Leiden, P.O. Box 9513 2300 RA Leiden, The Netherlands)
Christiane Helling ()

According to the currently available spherically symmetric models (Winters et al. 2000, A&A 361:641, Sandin & Hoefner 2003, A&A 404:789), a combination of stellar pulsation and radiation pressure on dust can be identified as the basic driving mechanism for the winds of AGB stars. This driving mechanism almost inescapably leads to the production of radial, onion-like dust shells in the models. However, observations seem to tell another story (e.g. Monnier et al. 2004, ApJ 605:436) with clear evidence for strong deviations from spherical symmetry.
In this presentation we will present new multi-dimensional models for C-star winds which include hydrodynamics with radiation pressure on dust grains, chemistry, time-dependent dust formation and simplified grey radiative transfer. A hydrostatic spherical black body is assumed as inner boundary condition (no pulsation).
These models reveal a much more complicate picture of the dust and wind formation as compared to the 1D models. Excited by hydrodynamical, radiative and thermal instabilities, dust forms from time to time in limited areas close to the star. These clouds are then accelerated outward by radiation pressure which creates gaps in the dust formation zone. These gaps are refilled not only by matter from the inside, but also by dust-free matter from the outside which falls back. A highly dynamical and turbulent dust formation zone is created in this way, which - in return - again bears a strongly inhomogeneous dust distribution. Further away from the star, flow instabilities (e.g. Rayleigh-Taylor) have time to modify and to shape the dust arcs/lanes/clouds produced in the dust formation zone.
http://www.strw.leidenuniv.nl/~woitke

Measuring the Magnetic Field on the Classical T Tauri Star TW Hydrae

Hao Yang (Rice University)
Christopher M. Johns-Krull (Rice University)
Jeff A. Valenti (Space Telescope Science Institute)

We present an analysis of infrared (IR) and optical echelle spectra of TW Hya. Using the optical data, we perform detailed spectrum synthesis to fit atomic and molecular absorption lines and determine key stellar parameters (T_eff, log(g), [M/H], vsini), finding a temperature a few hundred degrees warmer than implied by the K7 spectral type of this star. The IR spectrum is used to look for Zeeman broadening of photospheric absorption lines. We fit four Zeeman sensitive Ti I lines near 2.2 µm and find the average value of surface magnetic field. In addition several nearby magnetically insensitive CO lines show no excess broadening above that produced by stellar rotation. We will demonstrate our analysis, results, and implications.

A study of the star formation history for the galactic center stars

Zhi-yao Yu (Shanghai Astronomical Observatory)
Blum et al.(2003) present near-infrared H and K spectra for a magnitude-limited sample of 79 asymptotic giant branch and cool supergiant stars in the center of the Galaxy. They use neighborhood stars with known T_eff and M_bol that is in the same range as the Galactic Center(GC) sample to derive T_eff and M_bol for the GC sample. Using Blum et al(2003)'s observational results we study the relationships among the Galactic center star properties. Many interesting and important correlations are obtained. Using the correlations we have studied the star formation history for the GC.

Late-type field stars in the RASS at high galactic latitude

Franz-Josef Zickgraf (Hamburger Sternwarte)
Joachim Krautter (Landessternwarte Heidelberg)
Sabine Frink (Sterrewacht Leiden)

We present results of an investigation of a high-galactic latitude sample of late-type field stars detected in X-rays during the ROSAT All-Sky Survey (RASS). The sample comprises ≈200 G, K, and M stars. Lithium abundances were determined for ≈180 G-M stars. Radial velocities were measured for the ≈140 G and K type stars of the sample. Combined with proper motions these data were used to study the age distribution and the kinematical properties of the sample. Based on the lithium abundances half of the G-K stars were found to be younger than the Hyades (660Myr). A small subsample of 10 stars is younger than the Pleiades (100Myr). They are therefore most likely pre-main sequence stars. Kinematically the PMS stars appear to form a group with space velocities close to the Castor moving group but clearly distinct from the Local Association.

The coolest M-type subdwarf (sdM9.5), the nearest cool white dwarf (d=4pc), and other high proper motion discoveries

Hans Zinnecker (Astrophysikalisches Institut Potsdam)
Ralf-Dieter Scholz (Astrophysikalisches Institut Potsdam)
Ingo Lehmann & Israel Matute (MPE, Garching)

We report the discovery of seven high proper motion stars with proper motions between about 0.7 and 2.2 arcsec/yr. They were detected in an archival search using multi-epoch positions in the optical SuperCOSMOS Sky Surveys and in the near-infrared sky surveys 2MASS and DENIS. The star with largest proper motion, is spectroscopically classified as a very nearby (d=8pc) M5.5 dwarf with Galactic thin disk kinematics. A second star with about 2 arcsec/yr proper motion, is still lacking spectroscopic confirmation but can be classified from photometry as thick disk M3.5 dwarf. Three objects turn out to be cool subdwarf members of the Galactic thick disk or halo, including the first sdM9.5 object, which represents the currently coolest known M subdwarf, another ultra-cool subdwarf, of spectral type sdM7.0 as well as an earlier type (sdM1.5) star. The latter has an extremely large space velocity with clear halo kinematics. Two objects show featureless spectra typical of cool white dwarfs. One of them is probably a very nearby (d=4pc) thin disk object and may be the nearest isolated white dwarf, the other one has thick disk kinematics.

Acceleration of weakly collisional solar-type winds

Ioannis Zouganelis (LESIA - Paris Observatory France)
N. Meyer-Vernet (LESIA - Paris Observatory)
F. Pantellini (LESIA - Paris Observatory)

A major assumption inherent to the usual fluid solar wind models is that the plasma is dominated by collisions. Therefore the fluid approach implies that the particle velocity distribution functions are close to Maxwellians. However the observed solar wind electron distributions depart significantly from Maxwellians, indicating the limited validity of this hypothesis. Collisionless models are not fully justified either, but should bring some insights into the physics since heat transport is mainly driven by suprathermal particles which are virtually collisionless because of the rapid increase with energy of the Coulomb free path. A proper theory should take into account the transition from a fully collisional regime to a weakly collisional one. The existence of a plasma wind accelerated from subsonic to supersonic speeds depends mainly on the electrostatic field and the heat flux which are determined by the velocity distributions of particles. In this work we present recent developments of kinetic collisionless models of the solar wind and compare them with results obtained by numerical simulations that include collisions.

activity cycle of old solar type star HR 98

Jassur Davoud M.Z. (dept of theoretical physics and astrophysics,faculty of physics ,Tabriz University)
In an investigation of chromospheric and TR activity , the important diagnostic lines lie within the two wavelength bands of the IUE . The important indicators of activity in chromospheres are the emission lines OI ( 1305 A ) , CI / FeII ( 1560 A ) , CI / FeII ( 1658 A ) , SiII ( 1812 A ) , in short-wavelength region and Mg II ( 2800 A ) doublet in the long-wavelength region. Use of Mg II h and k lines as probes of chromospheric activity has the advantage of greater contrast over visible-band CaII observations , i.e. , a relatively greater ratio of line flux to continuum due to the fact that in cool stars the continuum falls off rapidly toward shorter wavelengths. The MgII h & k lines variability in old solar type star HR 98 was monitored from IUE Satellite during about 5 years from 1990 to 1995 and combined with other additional spectra taken by others since 1980. The time variability of Mg II h & k emission fluxes were measured against an adjacent spectrum portion in the Photospheric Mg II lines wing . This study shows that Mg II h & k lines change in a gradual and systematic manner . During 18 years there has been two activity minima ( around 1980 and 1992 ) and one maximum ( around 1986 ) , suggesting an activity cycle with a period of nearly 12 years which is comparable with solar one.
http://www.tabrizu.ac.ir

HETGS Spectroscopy of a Coronally Active Contact Binary, VW Cep

David Huenemoerder (MIT)
Adrienne Hunacek (MIT)

Short-period binaries represent the extreme in rotational-dynamo generated coronae. These stars are important for probing the origin and nature of coronae in the regimes of rapid rotation and activity saturation. VW Cep (P=0.28d) is relatively bright, partially eclipsing, and very active object. Light curves made from Chandra/HETGS data show flaring and rotational modulation, but no strong eclipses. Emission lines are broader than instrumental, indicating emission from both binary components. Further analysis will investigate emission measure and abundance distributions and density-sensitive line ratios in high and low flux states.
http://space.mit.edu/~dph

Comparison of wavelength dependent Giant Star Angular Diameters with models

Gerard van Belle (Caltech - Michelson Science Center)
David R. Ciardi (Caltech - Michelson Science Center)

We present angular size measurements obtained with the Palomar Testbed Interferometer (PTI). Our sample includes 82 giant stars, with spectral types between B7 and M7. These objects represent the `well studied' subset of giant stars observed at PTI (≥ 2 nights of observing per star, with an average of 17 samples per star). These objects have been rigorously vetted for binarity against the Hipparcos and FK6 catalogs. The PTI observations present `narrowband' angular sizes in 0.1 µm increments across the K band, from 1.95 to 2.45 µm, with narrowband channel centers located at 2.0, 2.1, 2.2, 2.3, and 2.4 µm. There is strong evidence for later spectral types for a systematic increase in their 2.4 µm sizes relative to the 2.2 µm near-continuum center pixel, with weaker evidence for a similar effect in the 2.3 µm channel. There is little if any evidence for similar size differences between the 2.0 and 2.1 µm channels, relative to the band center. By comparing this data to publicly available near-IR spectrophometric data for stars of similar spectral type, there is a clear correlation between the strength of spectral features, including the ¹²CO and ¹³CO bands that set in longwards of 2.29µm, and the narrowband angular size differences. Giant star atmospheric models corresponding to the PTI `narrowband' visibility data were generated from the extended model photospheres found in Bessel et al. (1989, 1991). For both the models and the observations, size ratios between the outlying wavelength pixels relative to the 2.2 µm center pixel may be generated, along with effective temperature (T_eff) estimates, and then compared. We find that for the stars with T_eff between 3000K and 4000K, the observed 2.4µm / 2.2µm size ratios are significantly higher than predicted by the models.
http://spider.ipac.caltech.edu/staff/gerard/

This document was translated from L^AT_EX by H^EV^EA.