The r-process in supernova explosions from the collapse of O-Ne-Mg cores

We examine r-process nucleosynthesis in a "prompt supernova explosion" from an 8-10 Msun progenitor star, as an alternative scenario to the "neutrino wind" mechanism. In the present model, the progenitor star has formed an oxygen-neon-magnesium core at its center. The core-collapse simulations are performed with a one-dimension, Newtonian hydrodynamic code. We obtain a very weak prompt explosion, in which no r-processing occurs. We further simulate energetic prompt explosions by enhancement of the shock-heating energy, in order to investigate conditions necessary for the production of r-process nuclei in such events. The highly neutronized ejecta (Ye = 0.14-0.20) leads to robust production of r-process nuclei; their relative abundances are in excellent agreement with the solar r-process pattern. Our results suggest that prompt explosions of 8-10 Msun stars with oxygen-neon-magnesium cores can be a promising site of r-process nuclei.