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, <SUP>13</SUP>C(α, n)<SUP>16</SUP>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 <SUP>13</SUP>C-pocket. This observation provides strong support to the suggestion of deep mixing of H into the He-intershell at low <SUP>13</SUP>C concentrations as a result of efficient transport of H through magnetic tubes.