Impact of rotation on the weak s-process

Abstract

The weak s process takes place in massive stars and it produces the majority of s-only isotopes in the atomic mass range from 60 to 90. This process is qualitatively well understood. However, there are still large uncertainties remaining on the quantitative side. Rotation has a strong effect on the stellar structure and mixing, but its impact on the s process has not been studied yet. We implemented an extended and flexible reaction network inside the Geneva stellar evolution code (GENEC) to be able to study the influence of rotation on the s process. For a star with a particular initial mass and composition rotation increases the He core size and the central temperature enhancing the s-process efficiency during core helium burning. In turn the C-shell contribution is reduced since more 22Ne has already been burnt during He-burning. Mixing induced by rotation also affects the contribution of the He-burning shell, since it leads to the production of primary 14N and primary 22Ne. 22Ne and 4He can again be transported to regions with higher temperatures below the convective He-shell, where 22Ne(alpha, n) becomes an efficient neutron source. To investigate the influence of reaction rate uncertainties besides the uncertainties of stellar structure and mixing, we have developed a one-zone post-processing network including Monte Carlo variations of the rates.