New Constraints on the Major Neutron Source in Low-mass AGB Stars

Abstract

We compare updated Torino postprocessing asymptotic giant branch (AGB) nucleosynthesis model calculations with isotopic compositions of mainstream SiC dust grains from low-mass AGB stars. Based on the data-model comparison, we provide new constraints on the major neutron source, 13 C( α , n ) 16 O in the He-intershell, for the s -process. We show that the literature Ni, Sr, and Ba grain data can only be consistently explained by the Torino model calculations that adopt the recently proposed magnetic-buoyancy-induced 13 C-pocket. This observation provides strong support to the suggestion of deep mixing of H into the He-intershell at low 13 C concentrations as a result of efficient transport of H through magnetic tubes.