Composition of the innermost core collapse supernova ejecta and the νp-Process

With presently known input physics and computer simulations in 1D, a self-consistent treatment of core collapse supernovae does not lead to explosions, while 2D models show some promise. Thus, there are strong indications that the delayed neutrino mechanism works combined with a multi-D convection treatment for unstable layers. On the other hand there is a need to provide correct nucleosynthesis abundances for the progressing field of galactic evolution and observations of low metallicity stars. The innermost ejecta is directly affected by the explosion mechanism, i.e. most strongly the yields of Fe-group nuclei for which an induced piston or thermal bomb treatment will not provide the correct yields because the effect of neutrino interactions is not included. We apply parameterized variations to the neutrino scattering cross sections and alternatively, parameterized variations to the neutrino absorption cross sections on nucleons in the "gain region". We find that both measures lead to similar results, causing explosions and a Ye larger than 0.5 in the innermost ejected layers, due to the combined effect of a short weak interaction time scale and a negligible electron degeneracy, unveiling the proton-neutron mass difference. The proton-rich environment results in enhanced abundances of 45Sc, 49Ti, and 64Zn as requested by chemical evolution studies and observations of low metallicity stars. Moreover, antineutrino capture on the free protons allows for an appreciable production of nuclei in the mass range up to A = 80 by the νp-process.