Masers & (Post-) AGB stars

General

  • new 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

 

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.

 

For More information, see the program webpage, and:

 

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

 

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

 

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.

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).

 

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:

 

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)