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

The following document lists the file abstract/TDEJONG_HCNFP.abs from catalogue VI/111.
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As a follow-up to our guaranteed time program AGBSTARS, we propose SWS
Fabry-Perot observations of Q-branch lines of HCN and C2H2 at around 14 micron
in four carbon stars and one S-type star. The goals of this proposal are:
(1) To detect HCN lines which are only just visible in our guaranteed time
observation with SWS01. (2) To determine the abundance, excitation temperature,
and turbulent velocity of C2H2 and HCN from the observed data using detailed
model calculations. The comparison of the results for the two molecules will
indicate the origin of the lines and the physical structure of the circum-
stellar shell. (3) The results will also be compared among the target stars
as a function of mass-loss rates and C/O ratios, to find the relation between
the excitation status of the molecules and other properties of the stars.
It is well know that HCN and C2H2 are two of the most abundant molecules
after CO in the atmosphere and the circumstellar shell of carbon stars.
C2H2 is one of the major source molecules for the carbon chemistry in the
circumstellar envelope. HCN is a key molecule concerning chemical processes
nitrogen involved. To understand the behavior of the two molecules in the
photospheres and the circumstellar shells of different types of star will
contribute to our knowledge of circumstellar chemistry. It is especially
important for C2H2, since this molecule cannot be observed by radio techniques.
On the other hand, the richness of the molecules in carbon stars means these
molecules could be a good probe for investigating physical structure of the
circumstellar envelope, such as temperature or turbulent velocity. The narrow
line separation in the Q-branch enables us to obtain information of several
lines together in a small scanning range. This makes the interpretation of
the data easier and increases the confidence of the results. ISO is the only
available instrument which can observe at 14 micron (outside the atmospheric
window) with a resolution of about 30000.




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