Convective-reactive nucleosynthesis of K, Sc, Cl and p-process isotopes in O-C shell mergers

We address the deficiency of odd-Z elements P, Cl, K and Sc in Galactic chemical evolution models through an investigation of the nucleosynthesis of interacting convective O and C shells in massive stars. 3D hydrodynamic simulations of O-shell convection with moderate C-ingestion rates show no dramatic deviation from spherical symmetry. We derive a spherically averaged diffusion coefficient for 1D nucleosynthesis simulations, which show that such convective-reactive ingestion events can be a production site for P, Cl, K and Sc. An entrainment rate of 10^-3M_⊙ s^-1 features overproduction factors OP_s ≈ 7. Full O-C shell mergers in our 1D stellar evolution massive star models have overproduction factors OP_m > 1 dex but for such cases 3D hydrodynamic simulations suggest deviations from spherical symmetry. γ - process species can be produced with overproduction factors of OP_m > 1 dex, for example, for ^{130, 132}Ba. Using the uncertain prediction of the 15M⊙, Z = 0.02 massive star model (OP_m ≈ 15) as representative for merger or entrainment convective-reactive events involving O- and C-burning shells, and assume that such events occur in more than 50 per cent of all stars, our chemical evolution models reproduce the observed Galactic trends of the odd-Z elements.