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First Stars III
Contact:
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Talk
Title: Evolution and nucleosynthesis of low-mass metal-poor AGB models with C- and N-enhanced molecular opacities Presenter: Sergio Cristallo Abstract: The concomitant overabundances of C, N and s-process elements are commonly ascribed to the complex interplay of nucleosynthesis, mixing and mass loss taking place in Asymptotic Giant Branch stars. Up to date, low temperature (T<4000 K) radiative opacity tables are available for scaled solar composition, so that only changes of H and He can be accounted for. Although the use of these tables substantially underestimates the radiative opacity of the cool atmosphere of an evolved AGB star eventually enriched in C and N (Marigo 2002), they are commonly adopted by stellar modelers, often left without alternative. With this work we make a step ahead. By means of the COMA code (Aringer 2000), we calculate opacity tables where C and N have been independently multiplied up to a factor of 2000; then, by means of the FRANEC stellar evolutionary code (Chieffi et al. 1998), we compute low mass metal-poor ([Fe/H]<-2) AGB models by interpolating over these new tables. In this way, we proper! ly take into account the C-enhancement caused by third dredge up episodes. We illustrate the changes induced by the use of these opacities on the physical and chemical properties of the models, with particular emphasis of the nucleosynthesis of carbon, nitrogen and s-process elements. Moreover, a possible N enhancement, caused by the cool bottom process or by the engulfment of protons into the convective zone generated by a thermal pulse and the subsequent huge third dredge up, is also considered. Finally, we discriminate between the two aforementioned scenarios and compare our results with the extant available observations.
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