Speaker
Description
The origin of the relatively high solar system abundances of certain proton-rich isotopes in the $90 < A < 100$ mass range has been an enduring mystery in nuclear astrophysics. An attractive proposal to solve this problem is called the $\nu p$-process. This process could operate in a hot bubble of a core-collapse supernova, which is formed by a neutrino-driven outflow from the surface of the protoneutron star (PNS) after the shock is launched. However, years of detailed studies have cast doubt over the ability of this process to generate sufficient yields of $^{92,94}$Mo and $^{96,98}$Ru, 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-$\alpha$ reaction. Here, we revisit the problem and present explicit examples of calculations, with 13 and 18 $M_\odot$ 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-$\alpha$ 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 $\nu p$-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 $\nu p$-process yields are found to vary significantly with the PNS mass and with the outflow character.
