S-Processing in Asymptotic Giant Branch Stars in the Light of Revised Neutron-Capture Cross Sections

Diego Vescovi,René Reifarth

doi:10.3390/universe7070239

Abstract

Current AGB stellar models provide an adequate description of the s-process nucleosynthesis that occurs. Nonetheless, they still suffer from many uncertainties related to the modeling of the 13C pocket formation and the adopted nuclear reaction rates. For many important s-process isotopes, a best set of neutron-capture cross sections was recently re-evaluated. Using stellar models prescribing that the 13C pocket is a by-product of magnetic-buoyancy-induced mixing phenomena, s-process calculations were carried out with this database. Significant effects are found for a few s-only and branching point isotopes, pointing out the need for improved neutron-capture cross section measurements at low energy.

Highlights

Asymptotic giant branch (AGB) stars are major production sources for heavy elements in the Universe
Differences larger than ∼10% are obtained for 122 Te, 134 Ba, 136 Ba, and 154 Gd, whose production has been decreased mostly due to an increased Maxwellian averaged cross sections (MACS) of the corresponding (n, γ) cross section
We investigated the effects induced by the adoption of a new neutroncapture cross section database on the s-process nucleosynthesis in low-mass AGB stars

Summary

Introduction

Asymptotic giant branch (AGB) stars are major production sources for heavy elements in the Universe They were recognized to be responsible for the nucleosynthesis of the main and strong components (nuclei heavier than Sr) of the solar s-process (slow neutron-capture process) distribution (see, e.g., Busso et al [1] for a review). Post-process calculations of such a 13 C reservoir have shown to be able to reproduce the distribution of s-elements in the solar main component [15], heavy-element isotopic compositions of presolar grains [16], and most of n-capture elements abundances observed in Ba-stars and post-AGB stars [17] These studies have been confirmed by numerical simulations of the formation of a magnetically-buoyancy-induced 13 C pocket in a new series of FRUITY stellar evolutionary models [18]. The results are compared with those obtained by the previously adopted set of (n, γ) cross sections and with isotopic ratios of heavy elements measured in presolar SiC grains

Stellar Models

Results and Discussion

Conclusions