Dusty Circumstellar Envelopes as Tracers of Evolutive Sequences of Carbon-Rich Stars

Details Dusty Circumstellar Envelopes as Tracers of Evolutive Sequences of Carbon-Rich Stars Dusty Circumstellar Envelopes as Tracers of Evolutive Sequences of Carbon-Rich Stars

Aug 2006

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2006iaujd..11e..19d&link_type=abstract

Pre-Solar Grains as Astrophysical Tools, 26th meeting of the IAU, Joint Discussion 11, 21 August 2006, Prague, Czech Republic, J

Astronomy and Astrophysics

Astrophysics

Scientific paper

During the Asymptotic Giant Branch phase, stars have a massive mass loss which leads to the formation of circumstellar dust envelopes. Therefore, the dust species formed in these media reflect the chemical composition of their photospheres. In the carbon-rich AGB environments, several compounds of dust are expected to be found, such as graphite, amorphous carbon and SiC. These dust species are the same ones revealed from analyses of individual dust grains extracted from the primitive meteorites. Based on the New Carbon Scheme of Classification (De Mello et al., in preparation) and in a numerical simulation method for solving the problem of radiative transfer in circumstellar envelopes (Lorenz-Martins & Pompéia 2000, MNRAS, 315, 856) we had determined a possible evolutive sequence for the carbon stars. The parameters applied, for a 50 star sample, in this discussion were the SiC-index, an estimative of the relative abundance between silicon-carbide to amorphous carbon, and the tau-index, an estimate of envelope opacity. Both can provide information about the evolutive stage of the carbon-rich stars. Thicker envelopes implies on tip-AGB stars and, high SiC/A.C. ratio points out to early stages of the AGB, as SiC grains may be mold in closer ranges to the star and therefore they may be the first grains that condensate in the carbon-rich star envelopes (McCabe 1982, MNRAS, 200, 71; Lorenz-Martins & Lefevre 1994, A&A, 291, 831). The pre-solar grain analyses are very important to improve our knowledge about dust compounds which may nucleate in circumstellar dust shells, like those of carbon-rich AGB stars. The examination of grains extracted from meteorites can improve substantially our knowledge on stellar evolution.

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