Full Synthesis Maps of Circumstellar SiCC

Details Full Synthesis Maps of Circumstellar SiCC Full Synthesis Maps of Circumstellar SiCC

May 1995

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1995adil...pg...01g&link_type=abstract

NCSA Astronomy Digital Image Library

Astronomy and Astrophysics

Astronomy

Abundance, Astronomical Interferometry, Astronomical Maps, Chemical Reactions, Radio Astronomy, Radio Spectra, Silicon Carbides, Spatial Distribution, Spectral Resolution, Spectrum Analysis, Stellar Envelopes, Velocity Distribution

Scientific paper

The molecule SiC2 in the circumstellar shell around the evolved star IRC+10216 has been mapped using the BIMA millimeter-wave interferometer. In this paper we present results of a full synthesis mapping of the 4(22)-3(21) transition of SiC2. This is an improvement over earlier interferometry of SiC2 because we have used single-element observations to fill in the central ``hole'' in the Fourier transform plane; data taken with the NRAO 12-meter telescope were combined with the interferometry to fully sample the u-v plane. A comparison of the full synthesis maps in the present work is made with previous interferometry of SiC2. Full synthesis maps show a clear shell-like structure with a bipolar symmetry. Our results indicate that SiC2 is distributed in a shell with inner and outer radii approximately 2 x 10^16 cm and approximately 6 x 10^16 cm, respectively. We estimate a fractional abundance, [SiC2]/[H2], of 1.4 x 10^-6. The fractional abundance of SiC2 in the inner envelope (approximately < 5 x 10^-8) is at least an order of magnitude less than the calculations of thermal equilibrium chemistry will allow. The most likely reason for the discrepancy is that silicon is rapidly incorporated into grains in the inner envelope; grain formation is not considered in the thermal equilibrium models. Implications for the chemistry and evolution of the circumstellar envelope are discussed.

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