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Masers & (Post-) AGB stars

Hamburger Sternwarte - Research


Masers & (Post-) AGB stars


General

Etoka S., Engels D., Imai H., et al. , 2014, OH masers in the Milky Way and Local Group galaxies in the SKA era, Advancing Astrophysics with the Square Kilometre Array, June 8-13, 2014, Giardini Naxos, Italy

Engels D., 2005,
AGB and post-AGB stars, Memorie della Societa Astronomica Italiana, v.76, p.441


Variability properties of OH/IR stars during the AGB - post-AGB transition

Using the Nançay Radio Telescope we monitor since 2013 a sample of several dozen OH/IR stars, which might be either pulsating AGB variables or post-AGB stars without regular large-amplitude variations. The goal is to study the changes in the variability properties during the evolutionary transition from the AGB to the post-AGB phase.

Program webpage

new Engels D., Etoka S., West M., Gérard E., 2017, OH masers as probes: How does the variability fade away during the AGB - post-AGB transition?,
In: Astrophysical Masers: Unlocking the Mysteries of the Universe, IAU Symposium 336, Cagliari, Italy, September 4-8, 2017,
Eds. A. Tarchi, M.J. Reid and P. Castangia, (in press)

Collaborators: D. Engels (Hamburg), S. Etoka (Manchester)


Distances to OH/IR stars using the phase-lag technique

We monitored between 2008 and 2012 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.

Program webpage

new Etoka S., Engels D., Gérard E., Richards A.M.S., 2017, Distances of Stars by mean of the Phase-lag Method,
In: Astrophysical Masers: Unlocking the Mysteries of the Universe, IAU Symposium 336, Cagliari, Italy, September 4-8, 2017,
Eds. A. Tarchi, M.J. Reid and P. Castangia, (in press)

Collaborators: D. Engels (Hamburg), S. Etoka (Manchester), E. Gérard, N. Hallet (Paris), A.M.S. Richards (Manchester)


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., 2015,
A database of circumstellar OH masers, A&A 582, A68

Version 2.4 released 2015, April 15
Go to Hamburg database new Go to eDAMS database

new Further publications

Collaborators: F. Bunzel, D. Engels, B. Heidmann


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).

Jiménez-Esteban F., Engels D., 2015,
Study of extremely reddened AGB stars in the Galactic bulge, A&A 579, A76

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)


Effelsberg/Medicina Monitoring Program -- 22 GHz H2O

We monitored between 1987 and 2011 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.

new 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)


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)


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