The nucleosynthesis of heavy elements in low-mass AGB stars

Abstract

We take 13C(α,n) 16O as netron source, allow for variation of the mass of the nucleus with thermal pulse number and adopt the unbranched s process path from 56Fe to 210Bi in an attempt to explain the overabundace of heavy elements in MS and S stars. We found stars with larger masses have larger dilution factors because of a stronger convection and that these stars fall in four different regions in the abundance diagram, thus enabling a rough estimate of the mass to be made. We show that, for a 2.5 M ⊙ star, the third dredge-up stops after a certain number of pulses because of the formation of a hollow shell structure, so the star will show no Tc and this can account for the existence of binary systems consisting of a “Tc-no” AGB star with a main-sequence star companion.