| Description |
Interstellar dust grains are thought to evolve in the colder regions
of space from the gas and solids there, material believed to have
come from Asymptotic Giant Branch (AGB) stars. The circumstellar
envelopes of such stars are also rich in complex molecules.
IRC+10216
is a well studied AGB star with a high mass loss rate. Close to
the Sun (~150 pc), it is an ideal place to study the physical and
chemical processes in AGB circumstellar envelopes.
Using the Submillimeter Array (SMA), we recently carried out the
first interferometric spectral line-survey of IRC+10216 in the 345
GHz band, with an angular resolution of 3"x2". 440 lines were
detected, with more than half for the first time, and about a hundred
lines that are as yet unassigned to known molecular transitions.
Following this line survey of IRC+10216, we observed two more evolved
stars: VY CMa and IK Tau, covering the same 870 microns window.
From the distribution of molecules we are obtaining their
abundances
and isotopologic abundance ratios. Using data for multiple
transitions
in a number of molecules we are deriving the physical conditions
in the circumstellar envelope to reach a picture of the star's
chemistry that can be compared with models. Our legacy surveys are
accompanied by a strong laboratory effort that helps with the
identification of possibly newly found molecules traced by
unidentified
lines. We also plan to create a publicly accessible database of
spectral-line channel-maps of the emission from all the lines
detected in these surveys.
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