THE ORIGIN OF CIRCUMSTELLAR SILICON-CARBIDE GRAINS FOUND IN METEORITES

Condensation calculations for C-rich circumstellar envelopes are used to model the condensation sequence of C, TiC, and SiC, and trace-element patterns observed in circumstelIlar SiC grains. Some properties of carbon star envelopes are briefly discussed, and condensation temperatures for major and trace elements are computed for a wide array of total pressure, C/O-ratios, and s-process elemental abundances. The comparison of calculated patterns for trace-element solid solutions in SiC with the different observed patterns measured by Amari et al. (1995) yields an association of the grains to at least three different groups of carbon stars.