Evolution and Nucleosynthesis of Low-Mass Metal-Poor AGB Models with C- and N-Enhanced Molecular Opacities.

Details Evolution and Nucleosynthesis of Low-Mass Metal-Poor AGB Models with C- and N-Enhanced Molecular Opacities. Evolution and Nucleosynthesis of Low-Mass Metal-Poor AGB Models with C- and N-Enhanced Molecular Opacities.

Mar 2008

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2008aipc..990..320c&link_type=abstract

FIRST STARS III: First Stars II Conference. AIP Conference Proceedings, Volume 990, pp. 320-324 (2008).

Physics

Giant And Subgiant Stars, Stellar Structure, Interiors, Evolution, Nucleosynthesis, Ages, Abundances, Chemical Composition, Population Ii Stars

Scientific paper

We use the COMA code to calculate radiative opacity coefficients for low temperature gas, where the abundances of C and N are enhanced up to a factor of 2000 with respect to a scaled solar composition. These opacities include the contributions of the most relevant atomic and molecular species. Then, by means of the FRANEC stellar evolutionary code, we compute low mass metal-poor ([Fe/H]<-2) AGB models by interpolating over the new opacity tables. In this way, we properly take into account the recurrent increase of the C abundance in the envelope caused by the third dredge up. We discuss changes induced by the use of these opacities on the physical and chemical properties of the models, with particular emphasis to the synthesis of carbon, nitrogen and s-process elements. We also consider the effects of a possible N enhancement, which may be caused by cool bottom process or by the engulfment of protons from the top of the convective zone generated by the first fully-developed thermal pulse. For a given metallicity, we find that it exists a lower mass limit for which normal AGB evolution occurs. On the contrary, stars with initial mass smaller than this limit, experience a proton engulfment during the first thermal pulse, which leads to a peculiar s-process nucleosynthesis, a low 12C/13C and to a significant synthesis of primary N. Finally, we compare our results with the observed chemical pattern of CEMP stars.

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