The weak s-process in massive stars, product for galactic chemical evolution and seed for explosive nucleosynthesis

The weak s-process in massive stars plays a crucial role in the nucleosynthesis of heavy elements between Fe and Sr. It is traditionally viewed as occurring primarily during the pre-supernova (pre-SN) phase, with minimal alteration from the ensuing core-collapse supernova (CCSN) explosion. In this study, we utilize a grid of 53 CCSN models spanning a wide range of progenitor masses and explosion energies and setups, to investigate the interplay between pre-SN s-process production and post-explosion modifications. We show that explosive contributions (without considering any contribution from neutrino-winds nucleosynthesis) can strongly alter the pre-SN isotopic abundance patterns of s-process nuclei. Also the impact of nuclear reaction rate uncertainties may vary depending on the CCSN explosion setup. We discuss the case of the C-fusion rate as example. We propose a revised framework where the weak s-process component clearly encompasses both direct production in stellar interiors and its indirect role as seeds for explosive nucleosynthesis. This dual contribution should be taken into account when comparing model predictions with observed galactic chemical evolution abundances and solar isotopic ratios, with direct implications also for understanding the origin of heavy isotopic abundances not made by the s s process.