Ther‐Process in Supernovae: Impact of New Microscopic Mass Formulae

The astrophysical origin of r -process nuclei is a long-standing mystery. Although some astrophysical scenarios show some promise, many uncertainties involved in both the astrophysical conditions and in the nuclear properties far from the β-stability have inhibited us from understanding the nature of the r -process. The purpose of the present paper is to examine the effects of the newly derived microscopic Hartree-Fock-Bogoliubov (HFB) mass formulae on r -process nucleosynthesis and analyze to what extent a solar-like r -abundance distribution can be obtained. The r -process calculations with the HFB-2 mass formula are performed, adopting the parameterized model of the prompt explosion from a collapsing O-Ne-Mg core for the physical conditions, and compared with the results obtained with the HFB-7 and droplet-type mass formulae. Because of its weak shell effect at the neutron magic numbers in the neutron-rich region, the microscopic mass formulae (HFB-2 and HFB-7) give rise to a spread of the abundance distribution in the vicinity of the r -process peaks ( A = 130 and 195). While this effect resolves the large underproduction at A ≈ 115 and 140 obtained with droplet-type mass formulae, large deviations compared to the solar pattern are found near the third r -process peak. It is shown that a solar-like r -process pattern can be obtained if the dynamical timescales of the outgoing mass trajectories are increased by a factor of about 2-3, or if the β-decay rates are systematically increased by the same factor.