Contents of: VI/111/./abstract/RSZCZERB_AGB_C_OH.abs

The following document lists the file abstract/RSZCZERB_AGB_C_OH.abs from catalogue VI/111.
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It is presently a widely accepted idea that single carbon stars are formed
during the evolution on the AGB when carbon rich material is dredged up,
probably during and/or just after a helium shell flash, from the interior of
the star to its oxygen rich photosphere (Iben and Renzini 1983, Ann. Rev.
Astr. Ap. 21, 271, Willems and de Jong 1988, AA 196, 173). The model of
Willems and de Jong, proposed after the discovery of carbon stars with
silicate dust emission, assumes that when the photosphere of the star becomes
carbon rich for the first time the mass loss rate strongly decreases compared
to the previous phase of evolution. In consequence, the detached oxygen rich
shell will expand around the carbon star which will become very soon visible.
Up to now 19 carbon stars with silicate emission are known (Kwok et al. 1997,
ApJS 112, 557). However, another signature of the oxygen rich envelope, the OH
maser emission, has been detected for only one of these sources.
Our recent investigations of the available data from OH surveys and the
published catalogue of the IRAS LRS spectra (Kwok et al. 1997) allowed us to
select a NEW group of sources which could be related to the transition phase
between oxygen and carbon stars. Namely, we have found 6 NEW carbon stars
which also show OH maser emission at 1612 MHz. These objects could be more
evolved than objects showing only silicate emission in their LRS spectra.
Probably, only after short lasting interruption mass loss resume again but
now with carbon based dust. We propose to obtain ISO SWS01 spectra in order to
better understand the transition between oxygen and carbon rich stars and to
constrain the behaviour of mass loss which leads to the so unexpected
phenomenon as an OH emission around carbon star.

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