NuGrid: s process in massive stars

TL;DR

This paper investigates the s-process nucleosynthesis in massive stars at low metallicity, highlighting the impact of primary 22Ne production due to rotation and introducing a new parallel post-processing code to model stellar nucleosynthesis.

Contribution

It demonstrates significant s-process element production driven by primary 22Ne in rotating massive stars and presents a new MPI-based code for detailed stellar nucleosynthesis modeling.

Findings

Large s-process production between Sr and Ba observed.

Reaction rate uncertainties, especially 17O(alpha,gamma), significantly affect results.

First comprehensive post-processing simulation from ZAMS to helium burning in a 15 solar mass star.

Abstract

The s-process production in massive stars at very low metallicities is expected to be negligible due to the low abundance of the neutron source 22Ne, to primary neutron poisons and decreasing iron seed abundances. However, recent models of massive stars including the effects of rotation show that a strong production of 22Ne is possible in the helium core, as a consequence of the primary nitrogen production (observed in halo metal poor stars). Using the PPN post-processing code, we studied the impact of this primary 22Ne on the s process. We find a large production of s elements between strontium and barium, starting with the amount of primary 22Ne predicted by stellar models. There are several key reaction rate uncertainties influencing the s-process efficiency. Among them, 17O(alpha,gamma) may play a crucial role strongly influencing the s process efficiency, or it may play a negligible role, according to the rate used in the calculations. We also report on the development of a new parallel (MPI) post-processing code (MPPNP) designed to follow the complete nucleosynthesis in stars on highly resolved grids. We present here the first post-processing run from the ZAMS up to the end of helium burning for a 15 solar mass model.