Thep-process in exploding rotating massive stars

Abstract

Context.Thep-process nucleosynthesis can explain proton-rich isotopes that are heavier than iron, which are observed in the Solar System, but discrepancies still persist (e.g. for the Mo and Rup-isotopes), and some important questions concerning the astrophysical site(s) of thep-process remain unanswered.Aims.We investigate how thep-process operates in exploding rotating massive stars that have experienced an enhanceds-process nucleosynthesis during their life through rotational mixing.Methods.With the Geneva stellar evolution code, we computed 25M⊙stellar models at a metallicity ofZ = 10−3with different initial rotation velocities and rates for the still largely uncertain17O(α,γ)21Ne reaction. The nucleosynthesis calculation, followed with a network of 737 isotopes, was coupled to stellar evolution, and thep-process nucleosynthesis was calculated in post-processing during both the final evolutionary stages and spherical explosions of various energies. The explosions were modelled with a relativistic hydrodynamical code.Results.In our models, thep-nuclides are mainly synthesized during the explosion, but not much during the ultimate hydrostatic burning stages. Thep-process yields mostly depend on the initial number of trans-iron seeds, which in turn depend on the initial rotation rate. We found that the impact of rotation on thep-process is comparable to the impact of rotation on thes-process. From no to fast rotation, thes-process yields of nuclides with mass numberA < 140 increase by 3−4 dex, and so do thep-process yields. Fast rotation with a lower17O(α, γ) rate significantly producess- andp-nuclides withA ≥ 140. The dependence of thep-process yields on the explosion energy is very weak.Conclusions.Our results suggest that the contribution of core-collapse supernovae from massive stars to the solar (and Galactic)p-nuclei has been underestimated in the past, and more specifically, that the contribution from massive stars with sub-solar metallicities may even dominate. A more detailed study including stellar models with a wide range of masses and metallicities remains to be performed, together with a quantitative analysis that is based on the chemical evolution of the Galaxy.