The p-process in exploding rotating massive stars

¹ Institut d’Astronomie et d’Astrophysique, Université Libre de Bruxelles, CP 226, 1050 Brussels, Belgium
e-mail: arthur.choplin@ulb.ac.be
² Astrophysics Group, Lennard-Jones Labs 2.09, Keele University, ST5 5BG Staffordshire, UK
³ National Astronomical Observatory of Japan, National Institutes of Natural Sciences, 2-21-1 Osawa, Mitaka, Tokyo 181-8588, Japan
⁴ Department of Astronomical Science, School of Physical Sciences, The Graduate University of Advanced Studies (SOKENDAI), 2-21-1 Osawa, Mitaka, Tokyo 181-8588, Japan
⁵ Kavli Institute for the Physics and Mathematics of the Universe (WPI), The University of Tokyo, 5-1-5 Kashiwanoha, Kashiwa, Chiba 277-8583, Japan
⁶ UK Network for Bridging the Disciplines of Galactic Chemical Evolution (BRIDGCE), UK
⁷ Department of Physics, Faculty of Science and Engineering, Konan University, 8-9-1 Okamoto, Kobe, Hyogo 658-8501, Japan
⁸ Geneva Observatory, University of Geneva, Chemin Pegasi 51, 1290 Sauverny, Switzerland

Received: 15 February 2022
Accepted: 25 March 2022

Abstract

Context. The p-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 Ru p-isotopes), and some important questions concerning the astrophysical site(s) of the p-process remain unanswered.

Aims. We investigate how the p-process operates in exploding rotating massive stars that have experienced an enhanced s-process nucleosynthesis during their life through rotational mixing.

Methods. With the Geneva stellar evolution code, we computed 25 M_⊙ stellar models at a metallicity of Z = 10⁻³ with different initial rotation velocities and rates for the still largely uncertain ¹⁷O(α,γ)²¹Ne reaction. The nucleosynthesis calculation, followed with a network of 737 isotopes, was coupled to stellar evolution, and the p-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, the p-nuclides are mainly synthesized during the explosion, but not much during the ultimate hydrostatic burning stages. The p-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 the p-process is comparable to the impact of rotation on the s-process. From no to fast rotation, the s-process yields of nuclides with mass number A <  140 increase by 3−4 dex, and so do the p-process yields. Fast rotation with a lower ¹⁷O(α, γ) rate significantly produces s- and p-nuclides with A ≥ 140. The dependence of the p-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.