The r-Process in Supernovae: Impact of New Microscopic Mass Formulas

Abstract

The astrophysical origin of $r$-process nuclei remains 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 $\beta$-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 formulas on the $r$-process nucleosynthesis and analyse 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 parametrized 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 formulas. Due to its weak shell effect at the neutron magic numbers in the neutron-rich region, the microscopic mass formulas (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 $A\approx 115$ and 140 obtained with droplet-type mass formulas, 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 $\beta$-decay rates are systematically increased by the same factor.

arXiv comment22 pages, 12 figures, accepted for publication in ApJ, some color figures converted to B&W due to size constraints

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• r-Process Calculations and Galactic Chemical Evolution
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• Application of the RMF mass model to the r-process and the influence of mass uncertainties
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• Massive Stars and their Supernovae
• Nuclear Weak Rates and Nuclear Weak Processes in Stars
• The strength of nuclear shell effects at N=126 in the r-process region
• Impact of the nuclear mass uncertainties on the r process