SiC Particle Composition and AGB Models

Details SiC Particle Composition and AGB Models SiC Particle Composition and AGB Models

May 1992

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1992aas...180.3707c&link_type=abstract

American Astronomical Society, 180th AAS Meeting, #37.07; Bulletin of the American Astronomical Society, Vol. 24, p.788

Astronomy and Astrophysics

Astronomy

Scientific paper

Pristine SiC particles found in meteorites contain large anomalies indicative of s-process material. A high (26) Mg abundance is seen in some grains and this is usually attributed to relict (26) Al. The Si and C are also anomalous. We have argued that the Si isotopic composition of the large SiC grains (particularly those with a ``platy'' morphology) implies processing in a He rich environment above 450 MK (Brown & Clayton 1992) capable of producing (alpha ,n) reactions on Mg isotopes. An AGB star origin for these particles implies a high intermediate mass (\gax 7 M_sun) progenitor to reach these temperatures in He shell flashes during the thermal pulse phase. Because of the highly correlated behavior of the Si isotopes in the ``platy'' particles, it is possible that this particular class of particles came from a single star. If so, the isotopic evolution of the outer envelope of an AGB star (or its stellar wind), should be able to produce particles with the observed distribution of isotopes. Both helium shell burning during thermal pulses and Hot Bottom Burning (HBB) at the base of the star's convective envelope will affect the surface isotopic composition. Using the parametrized models of Bazan (1991) and a stellar envelope code, we have investigated the isotopic evolution of the surface and the He shell of intermediate mass stars throughout their entire AGB phase. We present detailed tracks for the Si, C, Al, and Mg isotopic abundances to address whether the platy SiC grains could indeed have come from a single star. Bazan, G. 1991, Ph.D. thesis, University of Illinois Brown, L.E. & Clayton, D.D. 1992, ApJ Lett., in press

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