r-process nucleosynthesis in neutrino-driven winds from a typical neutron star with M = 1.4 M_⊙

We study the effects of the outer boundary conditions in neutrino-driven winds on r-process nucleosynthesis. We perform numerical simulations of hydrodynamics of neutrino-driven winds and nuclear reaction network calculations. As an outer boundary condition of hydrodynamic calculations, we set a pressure upon the outermost layer of the wind, which is approaching toward the shock wall. Varying the boundary pressure, we obtain various asymptotic thermal temperatures of expanding material in the neutrino-driven winds for resulting nucleosynthesis. We find that a slightly lower asymptotic temperature reduces the charged particle reaction rates and the resulting amount of seed elements and leads to a high neutron-to-seed ratio for a successful r-process abundance pattern, which is in reasonable agreement with the solar system r-process abundance pattern. As a result, the asymptotic temperature, slightly lower than those in previous studies of neutrino-driven winds, can lead to a successful r-process even for the typical proto-neutron star mass M_NS ∼ 1.4 M_⊙. We also explore the relation between the boundary condition and the neutron star mass, which is related to the progenitor mass, for a successful r-process.