The r-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, ∼ 100N _Ak-200N _Ak, and a neutrino luminosity as high as ∼10⁵² 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 protoneutron 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 protoneutron star by accretion after a failed initial neutrino burst.