AAS 206th Meeting, 29 May - 2 June 2005
Session 6 Formation and Fate of Stardust
Poster, Monday, 9:20am-6:30pm, Tuesday, 10:00am-7:00pm, May 30, 2005, Ballroom A

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[6.05] The Nature and Evolution of Silicon Carbide in the Outflows of Carbon Stars

G. D. Thompson, A. K. Speck (University of Missouri - Columbia), A. M. Hofmeister (WUSTL)

It has been known for more than three decades that dust particles form in the atmospheres of cool stars and are ejected into the interstellar medium. In this context there has been a great deal of observational, theoretical and laboratory studies of silicon carbide (SiC).

Theoretically SiC is expected to form in the outflows of carbon stars and has indeed been observed in the form of an 11.3um feature in the mid-IR spectrum of such stars. SiC has also been found in meteorites, and from isotopic studies, many of these grains are believed to have formed around carbon stars. Results from the study of these presolar meteoritic SiC grains suggest that the nature of the SiC forming in carbon star outflows changes as the star evolves. Theory predicts that the abundance of s-process elements in the atmospheres of such a star should increase as the star evolves. It has been shown that the smaller presolar SiC grains contain a higher abundance of s-process elements, suggesting that grain formation initially produces relatively large grains, and that the grains formed are progressively smaller as the star evolves. We present observational evidence that confirms this suggestion and discuss the meaning of the change in grain size with stellar evolution.

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Bulletin of the American Astronomical Society, 37 #2
© 2005. The American Astronomical Soceity.