Convective-reactive events which lead to C/O shell mergers in massive stars
have unique nucleosynthetic signatures similar to H ingestion and i process in
AGB stars. We investigate the dynamics of the O shell with C ingestion under
convective-reactive conditions with 3D hydrodynamic simulations and derive an
entrainment rate of 1e-7 Msun/s. Informed by hydrodynamic simulation we model
the comprehensive nucleosynthesis in O-C shell mergers in 1D. We find for large
entrainment rates expected during a shell merger the efficient production of
odd-Z elements. In particular the strong production of K and Sc can explain the
current underproduction in Galactic chemical evolution models compared to halo
and disk stars.
These findings are in agreement with O-C shell mergers in stellar models of the JINA/NuGrid model and yield database. Such mergers boost the production of p-process nuclei by many factors by providing fresh seed nuclei from the C shell.