A Spectral Survey of Evolved Stars

Details A Spectral Survey of Evolved Stars A Spectral Survey of Evolved Stars

Dec 2007

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2007aas...21110001k&link_type=abstract

American Astronomical Society, AAS Meeting #211, #100.01; Bulletin of the American Astronomical Society, Vol. 39, p.911

Astronomy and Astrophysics

Astronomy

Scientific paper

We report a spectral line survey of the circumstellar envelopes of evolved stars using the Arizona Radio Observatory 12 m and 10 m telescopes, covering the frequency ranges from 71-161 GHz and 218-268GHz. Our sample consists of the AGB stars IRC 10216 and CIT 6, the proto-planetary nebula AFGL 2688, and the young planetary nebula NGC 7027. The data allow us to investigate the chemistry processes in different physical environments and evolutionary stages. A total of more than 500 emission features (mostly rotational transitions of molecules) are detected in the survey. Our observations show that the sources in different evolutionary stages have remarkably different chemical composition. As a star evolves from AGB stage to proto-planetary nebula, the abundances of Si-bearing molecules (SiO, SiCC, and SiS) decrease, while the abundances of some long-chain molecules, such as CH3CN, C4H, and HC3N, increase. After further evolution to the planetary nebula stage, the abundances of neutral molecules decrease, and the emission from molecular ions becomes more intense. These differences can be attributed to the changes of the role that dust, stellar wind, shock wave, and UV/X-ray from the central star play in different evolutionary stages. These results will provide significant constraints on models of circumstellar chemistry.

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