Composition of the Innermost Core‐Collapse Supernova Ejecta

With presently known input physics and computer simulations in 1D, aself-consistent treatment of core collapse supernovae does not yet lead tosuccessful explosions, while 2D models show some promise. Thus, there arestrong indications that the delayed neutrino mechanism works combined with amulti-D convection treatment for unstable layers. On the other hand there is aneed to provide correct nucleosynthesis abundances for the progressing field ofgalactic evolution and observations of low metallicity stars. The innermostejecta is directly affected by the explosion mechanism, i.e. most strongly theyields of Fe-group nuclei for which an induced piston or thermal bomb treatmentwill not provide the correct yields because the effect of neutrino interactionsis not included. We apply parameterized variations to the neutrino scatteringcross sections and alternatively, parameterized variations are applied to theneutrino absorption cross sections on nucleons in the ``gain region''. We findthat both measures lead to similar results, causing explosions and a Ye>0.5 inthe innermost ejected layers, due to the combined effect of a short weakinteraction time scale and a negligible electron degeneracy, unveiling theproton-neutron mass difference. We include all weak interactions (electron andpositron capture, beta-decay, neutrino and antineutrino capture on nuclei, andneutrino and antineutrino capture on nucleons) and present firstnucleosynthesis results for these innermost ejected layers to discuss how theyimprove predictions for Fe-group nuclei. The proton-rich environment results inenhanced abundances of 45Sc, 49Ti, and 64Zn as requested by chemical evolutionstudies and observations of low metallicity stars as well as appreciableproduction of nuclei in the mass range up to A=80.Comment: 13 pages, 8 figures. Final versio