Ther‐Process in Neutrino‐driven Winds from Nascent, “Compact” Neutron Stars of Core‐Collapse Supernovae

We present calculations of r -process nucleosynthesis in neutrino-driven winds from the nascent neutron stars of core-collapse supernovae. A full dynamical reaction network for both the α-rich freezeout and the subsequent r -process is employed. The physical properties of the neutrino-heated ejecta are deduced from a general relativistic model in which spherical symmetry and steady flow are assumed. Our results suggest that proto-neutron stars with a large compaction ratio provide the most robust physical conditions for the r -process. The third peak of the r -process is well reproduced in the winds from these "compact" proto-neutron stars even for a moderate entropy, ~ 100 N A k -200 N A k , and a neutrino luminosity as high as ~10 52 ergs s -1 . This is due to the short dynamical timescale of material in the wind. As a result, the overproduction of nuclei with A ≲ 120 is diminished (although some overproduction of nuclei with A ≈ 90 is still evident). The abundances of the r -process elements per event is significantly higher than in previous studies. The total integrated nucleosynthesis yields are in good agreement with the solar r -process abundance pattern. Our results have confirmed that the neutrino-driven wind scenario is still a promising site in which to form the solar r -process abundances. However, our best results seem to imply both a rather soft neutron-star equation of state and a massive proto-neutron star that is difficult to achieve with standard core-collapse models. We propose that the most favorable conditions perhaps require that a massive supernova progenitor forms a massive proto-neutron star by accretion after a failed initial neutrino burst.