The γ-process nucleosynthesis in core-collapse supernovae

Abstract

Context. The γ-process nucleosynthesis in core-collapse supernovae is generally accepted as a feasible process for the synthesis of neutron-deficient isotopes beyond iron. However, crucial discrepancies between theory and observations still exist: the average yields of γ-process nucleosynthesis from massive stars are still insufficient to reproduce the solar distribution in galactic chemical evolution calculations, and the yields of the Mo and Ru isotopes are a factor of ten lower than the yields of the other γ-process nuclei. Aims. We investigate the γ-process in five sets of core-collapse supernova models published in the literature with initial masses of 15, 20, and 25 M⊙ at solar metallicity. Methods. We compared the γ-process overproduction factors from the different models. To highlight the possible effect of nuclear physics input, we also considered 23 ratios of two isotopes close to each other in mass relative to their solar values. Further, we investigated the contribution of C–O shell mergers in the supernova progenitors as an additional site of the γ-process. Results. Our analysis shows that a large scatter among the different models exists for both the γ-process integrated yields and the isotopic ratios. We find only ten ratios that agree with their solar values, all the others differ by at least a factor of three from the solar values in all the considered sets of models. The γ-process within C–O shell mergers mostly influences the isotopic ratios that involve intermediate and heavy proton-rich isotopes with A > 100. Conclusions. We conclude that there are large discrepancies both among the different data sets and between the model predictions and the solar abundance distribution. More calculations are needed; particularly updating the nuclear network, because the majority of the models considered in this work do not use the latest reaction rates for the γ-process nucleosynthesis. Moreover, the role of C–O shell mergers requires further investigation.

Production of 44Ti and Iron-group Nuclei in the Ejecta of 3D Neutrino-driven Supernovae

“…We do not find any significant creation of isotopes with A > 84 in the material covered by our postprocessing. However, we do not include all of the O/Ne regions that may contribute to the p-nuclei and other isotopes via the γ process (Roberti et al 2023). Overall, the abundance pattern we find is similar to that from the 2D model s11 of Wanajo et al (2018), but with a slightly larger neutron-rich component in our case.…”

Zero and Extremely Low-metallicity Rotating Massive Stars: Evolution, Explosion, and Nucleosynthesis Up to the Heaviest Nuclei

“…The possible occurrence of a merging of the O convective shell in the C-rich zone is of great interest because it would reduce the yields of the products of the C burning and increase those of the O burning. The reason is that the merging spreads the products of the C burning down to the base of the O convective shell (where they are easily destroyed by the passage of the shock wave), and, vice versa, it spreads out the products of the O burning where they can survive to the passage of the shock wave (seeRitter et al 2018;Roberti et al 2023; and …”

The s process in massive stars, a benchmark for neutron capture reaction rates

“…The variations beyond the y-axis scale at the end of the He-core are due to the protonrich nuclei ( 74 Se, 78 Kr, 84 Sr, 92 Mo and 98 Ru). These isotopes are made by the p-process in supernovae [29,69,70], and they are destroyed here by the s process. Therefore, those variations are not relevant for their stellar production.…”