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OH masers as probes: How does the variability fade away during the AGB - post-AGB transition?

Published online by Cambridge University Press:  16 July 2018

D. Engels
Affiliation:
Hamburger Sternwarte, Universität Hamburg, Germany, email: dengels@hs.uni-hamburg.de
S. Etoka
Affiliation:
Jodrell Bank Centre for Astrophysics, University of Manchester, UK, email: sandra.etoka@googlemail.com
M. West
Affiliation:
Hartebeesthoek Radio Astronomy Observatory, South Africa, email: marion@hartrao.ac.za
E. Gérard
Affiliation:
GEPI, Observatoire de Paris, Meudon, France, email: eric.gerard@obspm.fr
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Abstract

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We are currently performing a monitoring program of the 1612 MHz OH maser emission of several dozen Galactic disk OH/IR stars with the Nancay Radio Telescope (NRT). They are complemented by several OH/IR stars toward the Galactic center, which were monitored with the Hartebeesthoek radio telescope. We use the maser variations to probe the underlying stellar variability. As early monitoring programs already have shown, some stars are large amplitude variables with periods up to 7 years, others show small or even no amplitude variations. This dichotomy in the variability behaviour is assumed to mark the border between the AGB and the post-AGB stages. With the current program, we wish to find objects in transition and to describe their variability properties. We consider the fading out of pulsations with steadily declining amplitudes as a viable process. Promising candidates in the disk are the small-amplitude variables OH 138.0+7.2 and OH 51.8−0.2. ’Non-variable’ OH/IR stars in the Galactic center region may be as frequent as in the disk.

Type
Contributed Papers
Copyright
Copyright © International Astronomical Union 2018 

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