Speaker
Description
Standard massive star models systematically underproduce odd-Z intermediate mass elements (P, Cl, K, and Sc) relative to observed stellar abundances, especially at low metallicity. Recent studies suggest that this discrepancy can be accounted for if a fraction of massive stars undergo a carbon–oxygen shell merger occurring in the final days to seconds before core-collapse supernova. During such a merger, the oxygen-burning convective shell expands outward into the adjacent C-rich and Ne-rich layer. The chain of reactions generated in this event may significantly enhance the production of these elements, providing a possible solution to their puzzling galactic origin. Here, we present new insights into the role of convective boundary mixing (CBM) on nucleosynthesis. The efficiency of mixing at convective boundaries directly influences the occurrence of shell mergers and determines the size of the resulting merged convective region. We performed nucleosynthesis calculations using the NuGrid post-processing tools on the stellar models of Whitehead et al. (2026). These models incorporate the CBM prescription of Scott et al. (2021), in which the CBM strength varies with initial mass. This results in a stronger CBM than typically assumed in previous 1D models, which generally adopt a fixed CBM strength independent of stellar mass. We investigate the impact of this improved CBM on shell merger at low metallicity (Z = 10−3), with particular emphasis on the role of the merger in the nucleosynthesis of odd-Z intermediate-mass elements.