S-process nucleosynthesis in primordial AGB stars

Abstract

Despite the lack of iron seeds and provided partial mixing of protons takes place below the convective envelope, it is shown that the production of s-process elements can be efficient in primordial AGB stars. The synthesis proceeds as follows: neutrons are mainly produced by the 13C(α,n) 16O reaction and captured by the abundant CNe isotopes to synthesized heavier species which will then serve as efficient seed elements for the s-process thanks to their larger neutron cross sections. When the bottleneck formed by the 33S(n,α) 30Si is passed, the synthesis of s-elements proceeds in a standard way. Under the assumption that protons can diffuse below the envelope, primordial AGB stars are expected to be s-process enriched and to exhibit strong signatures of Pb and Bi.