Neutron-capture nucleosynthesis in AGB stars

摘要: Recent AGB models including diffusive overshoot or rotational effects suggest the partial mixing (PM) of protons from H-rich envelope into C-rich layers during third dredge-up. In order to study impact such a on surface abundances, nucleosynthesis calculations based stellar are performed for different assumptions (ranging X mix p =1 0 6 0.7) in PM zone. For high proton-to- 12 C abundance ratios, light nuclei as fluorine and sodium efficiently produced, while heavier s- process synthesized lower ratios. framework model, assuming smooth expo- nentially decreasing proton profile, 19 F evolution is correlated with that s-process agree- ment observations. However, function C/O ratio, enrichment remains dif- ficult reconcile observations stars. Sodium predicted be produced small region zone ratio about 10, but large overproduction factors (up fifty times higher than left over by hydrogen burning shell). The primary 13 pocket formed at low ratios responsible an efficient production nuclei. A table elemental overabundances pre- dicted stars four metallicities presented. All shown suffer major nuclear reaction rate uncertainties, particular, C(p ;) 14 N , N(n;p) 22 Ne( ;n) 25 Mg . uncertainties associated amount mixed found extent rather adopted H profile. Finally, scenario predicts low-metallicity enriched elements should exhibit Pb Bi compared other s-isotopes. search Pb-stars highly encouraged.