Review
Engels D., 2005,
AGB and post-AGB stars, Memorie della Societa Astronomica Italiana, v.76, p.441
Distances to OH/IR stars using the phase-lag technique
We monitor since 2008 the 1612 MHz OH maser emission of about 20 OH/IR stars
using the Nançay Radio Telescope
to determine the phase-lag between the variations of the two maser peaks
coming from the front and rear part of the circumstellar shell. The
linear diameter obtained from the phase-lag can be combined with an
angular distance from an interferometric observation to yield the distance
of the star.
Status of the program
Engels D., Etoka S., Gerard E., Hallet N., 2013,
Poster presented at
The Modern Radio Universe 2013
2013 April 22 - April 26, Bonn, Germany
Collaborators:
D. Engels, S. Etoka (Hamburg), E. Gérard, N. Hallet (Paris)
Effelsberg/Medicina Monitoring Program -- 22 GHz H2O
We monitor late-type stars in the 22 GHz maser line of water using
the radio telescopes in
Effelsberg and
Medicina.
Water vapour masers in long-period variable stars
We monitored a couple of Semiregular variable stars, Mira
variables, OH/IR stars, and Supergiants to access their
variability properties. For a few, VLA maps to analyze the
variations of the spatial distribution of the maser sites
were obtained.
Published results
see:
Results for RX Boo and SV Peg
Data
Water vapour masers in Post-AGB stars
Stars departing from the AGB and now probably evolving to the
Planetary Nebula stage show peculiar water maser properties. A
summary of 10 years observations of
four
Post-AGB stars was published in 2002.
Other AGB stars
The complete set of observations is available here. You may browse
the object
catalogue for particular sources.
Collaborators:
J. Brand (Bologna),
D. Engels
(Hamburg) ,
A. Winnberg (Onsala)
Database of circumstellar masers
Compilation of galactic stellar sources observed
for OH maser emission in the transition at 1612, 1665, and
1667 MHz. Extension to H2O and SiO maser emission
is in work.
Engels D., Bunzel F., 2008,
Poster presented at
IAU Symposium 242, Astrophysical Masers and Their Environments
2007 March 12-16, Alice Springs, Australia
Engels D., Heidmann, B. 2011,
Poster presented at
Why Galaxies Care About AGB stars II.,
2010 August 16-20, Vienna, Austria
Engels D. 2012,
Poster presented at
Cosmic masers - From OH to H0, IAU Symposium 287
2012 January 29 - February 3, Stellenbosch, South-Africa
Version 2.2 released 2012, June 26
Go to the database
Collaborators:
F. Bunzel, D. Engels, B. Heidmann
Lifetime of 1612 MHz OH maser in circumstellar shells
We find that the lifetime of 1612 MHz OH maser emission in the
circumstellar shells of OH/IR stars is >2800 years (1σ).
Engels D., Jimenez-Esteban F., 2007
Lifetime of OH masers at the tip of the asymptotic giant branch,
A&A 475, 941
Infrared and optical monitoring of Arecibo OH/IR stars
We monitored 1999 - 2005 OH/IR stars (long-period variables on the Asymptotic Giant Branch)
from the Arecibo Survey in the infrared with several telescopes in Spain
and a few of them in the optical with our
own 1.2m Oskar-Lühning-Telescope.
Finding Charts for the optical monitoring:
Arecibo OH/IR
stars (Hamburg version)
Finding Charts for the infrared monitoring:
Arecibo OH/IR
stars (Madrid version)
Related papers:
Jimenez-Esteban F.M., Garcia-Lario P., Engels D., Manchado A. , 2006,
Near-IR variability properties of a selected sample of AGB stars, A&A 458, 533
Jimenez-Esteban F.M., Garcia-Lario P., Engels D., Perea Calderon J.V., 2006,
An infrared study of galactic OH/IR stars.
II. The "GLMP sample" of red oxygen-rich AGB stars, A&A 446, 773
Jimenez-Esteban F.M., Agudo-Merida L., Engels D., Garcia-Lario P., 2005,
An infrared study of galactic OH/IR stars.
I. An optical/near-IR atlas of the Arecibo sample, A&A 431, 779
Collaborators:
D. Engels (Hamburg),
F. Jiménez-Esteban, Pedro García-Lario, Laura Agudo-Mérida (Madrid),
I. Brott, C. Hühn (Hamburg)
Extremely red OH/IR stars
At the very end of AGB evolution stars are hidden from optical and
sometimes also from near-infrared view (λ<2.2μm). To search for
such extremely red OH/IR stars we search for infrared counterparts to
OH maser sources in the IRAS, MSX and 2MASS catalogues and we identify
candidates directly in the infrared point source catalogues based on
colors and other criteria. Currently we are working on a sample of
OH/IR stars discovered until 1980, which is yet not fully identified
(the Baud sample), and on a sample of very red IRAS sources selected
by color and variability index VAR>50 (the GLMP sample).
The Baud sample:
Baud catalogue
The Extreme sample:
GLMP sample:
Extremely red IRAS variables
Collaborators:
D. Engels (Hamburg),
F. Jiménez-Esteban, Pedro García-Lario, José V. Perea Calderón (Madrid)
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