Contents of: VI/111/./abstract/CSKINNER_CO_OBS_2.abs

The following document lists the file abstract/CSKINNER_CO_OBS_2.abs from catalogue VI/111.
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==> In this proposal, more time is being requested for CSKINNER.CO_OBS
In this proposal, we proposed high spectral resolution observations of high
level CO emission lines in a sample of evolved stars, in order to study the
evolution of the winds and circumstellar envelopes from the AGB to the PN
phases. We will determine the thermal structure of the circumstellar gas
shells, as well as the mass-loss rates during the superwind phase. The sample
of objects chosen for the study includes AGB stars with low, intermediate and
very high mass-loss rates, post-AGB stars with low, intermediate and high
central star temperatures, and low- and high-excitation PN. Both O-rich and
C-rich examples of each type are included. The CO observations will be
modelled using a full radiative transfer code in the comoving frame in the
case of AGB stars and the coolest post-AGB stars, whilst for the post-AGB
stars and PN we will use modified codes originally written for the study of
photodissociation regions which we have already used succesfully to model KAO
observations of CO in a few of the brightest of such sources. The results will
allow us to follow the evolution of physical conditions (gas temperature and
density) in the hottest, densest parts of the circumstellar envelopes, close
to the central stars.  We have not yet received any data from this proposal.
However, we do have grating spectra of a number of AGB stars showing that high
rotational lines of CO are indeed present at strengths as high as we predicted.
Since our brightest target, IRC+10216, was not observed before it disappeared
from ISO's view, and our grating spectra confirm the presence of CO lines in
AGB star spectra, we propose to add a three AGB stars to our small survey.  We
also wish to add one post-AGB star, CRL618, which would not originally have
been observable from an Autumn launch, but will reappear towards the end of
the mission because of the longer than expected life.

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