Successful νp-process in neutrino-driven outflows in core-collapse supernovae

The origin of the relatively high solar system abundances of certain proton-rich isotopes in the 9092,94Mo and ^96,98Ru, as a well as to predict the correct abundance ratios of these isotopes to other p-nuclides. These difficulties became more dire with the recent calculations that took into account in-medium effects enhancing the rate of the triple-α reaction. Here, we revisit the problem and present explicit examples of calculations, with 13 and 18 M⊙ progenitor masses, in which both the required absolute yields of the Mo and Ru p-nuclides and the observed isotopic ratios are successfully reproduced, even with the enhanced triple-α rates taken into account. The models are characterized by entropy-per-baryon values in the 80-to-90 range and by subsonic outflow profiles. Optimal conditions for the νp-process are reached at different post-bounce times for different progenitor masses, but always within the first 2-3 seconds after the start of the explosion. To obtain the required entropy values at this stage of the explosion---given the available nuclear equations of state---requires a relatively heavy PNS. This suggests that the Mo and Ru p-nuclides observed in the Solar System were made in CCSN explosions characterized by an extended accretion stage. At the same time, the νp-process yields are found to vary significantly with the PNS mass and with the outflow character.