The rp-Process in Neutrino-driven Winds

Recent hydrodynamic simulations of core-collapse supernovae with accurate neutrino transport suggest that the bulk of the early neutrino-heated ejecta is proton rich, in which the production of some interesting proton-rich nuclei is expected. As suggested in recent nucleosynthesis studies, the rapid proton-capture (rp) process takes place in such proton-rich environments by bypassing the waiting point nuclei with β⁺-lives of a few minutes via the faster capture of neutrons continuously supplied from the neutrino absorption by protons. In this study, the nucleosynthesis calculations are performed with a wide range of neutrino luminosities and electron fractions (Y_e), using semianalytic models of proto-neutron-star winds. The masses of proto-neutron stars are taken to be 1.4 and 2.0 M_solar, where the latter is regarded as the test for somewhat high-entropy winds (about a factor of 2). For Y_e>0.52, the neutrino-induced rp-process takes place in many wind trajectories, and p-nuclei up to A~130 are synthesized in interesting amounts. However, ⁹²Mo is somewhat underproduced compared to other p-nuclei with similar mass numbers. For 0.46<Y_e<0.49, on the other hand, ⁹²Mo is significantly enhanced by the nuclear flows in the vicinity of the abundant ⁹⁰Zr that originates from the α-process at higher temperature. The nucleosynthetic yields are averaged over the ejected masses of winds, and further, over the Y_e distribution predicted by a recent hydrodynamic simulation of a core-collapse supernova. Comparison of the Y_e- and mass-averaged yields to the solar compositions implies that the neutrino-driven winds can potentially be the origin of light p-nuclei up to A~110, including ^92,94Mo and ^96,98Ru, that cannot be explained by other astrophysical sites.