The following document lists the file abstract/ROUDMAYE_OUD_01.abs
from catalogue VI/111.
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Post-Asymptotic Giant Branch (post-AGB) stars are objects that are in the short transition between the AGB and the Planetary Nebula phase. Observations of these objects provide important information on the knowledge of this phase of evolution, and help to constrain and improve theoretical evolutionary models. The known sample of post-AGB objects however is strongly biased towards objects that left the AGB only a few hundred years ago, far less than the expected transition time of 1000 to even 10,000 years. This difference is basically due to a selection effect; searches in the IRAS Point Source Catalog always required at least a detection at 12 micron, biasing towards objects with hot dust, close to the star. The aim of this proposal is to study a very carefully selected sample of candidate post-AGB stars with very cool dust shells, which we believe to represent the older, not previously studied, post-AGB stars. To study their photospheres we have obtained extensive sets of optical and ultraviolet spectroscopy. Now we wish to study their circumstellar environment using ISO, which is the only platform with the sensitivity and wavelength coverage to do this. We propose to obtain medium resolution SWS-01 spectra combined with PHOT-P and PHOT-C photometry. The observations will be used to derive the properties of the circumstellar environment of the objects, in particular the mass loss rates, the chemistry of the circumstellar envelopes, and the kinematic ages of the dust shells. These objects are expected to be much further in their (post-AGB) evolution than the existing sample of post-AGB stars. The observations will be compared to post-AGB objects listed in the Central Program, which will yield important information on the effects of the evolution of the circumstellar shells during the post-AGB phase. In addition, the observations can be used to constrain models that predict the transition time scales from the AGB to the PN phase.