Nucleosynthesis in Neutrino-driven Winds in Hypernovae

by Mr Sho Fujibayashi

Monday 15 Feb 2016, 13:30 → 14:30 Asia/Tokyo

Main Research Building 433 (RIKEN Wako)

Date: Feb 15 (Mon) Time: 13:30 - Place: Main Research bldg. 433 Speaker: Sho Fujibayashi (Kyoto University) Title: Nucleosynthesis in Neutrino-driven Winds in Hypernovae Abstract: The origin of the elements heavier than iron is not fully understood. For decades, neutrino-driven winds blown off from proto-neutron stars (PNSs) are considered to be the most promissing cite for $r$-process. However, recent researches indicate that the $r$-process in the neutrino-driven winds from normal PNSs does not occur sufficiently to produce the third peak elements. We investigate the nucleosynthesis in the neutrino driven winds blown off from a $3M_\odot$ massive PNS temporarily formed during the collapse of a $100M_\odot$ star. We construct the steady and spherically symmetric wind solutions. We set large neutrino luminosities ($\sim 10^{53}\ {\rm erg\ s^{-1}}$) and average energies of electron neutrinos and antineutrinos ($\epsilon_{\nu_e}$, $\epsilon_{\bar{\nu}_e}$) based on a recent numerical relativity simulation. The wind solutions indicate much shorter temperature-decrease timescale than that of the winds from normal PNSs and, depending on $\epsilon_\nu$, the winds can be both neutron-rich and proton-rich. In the neutron-rich wind, the $r$-process occurs and the abundance distribution of a fiducial wind model of the mPNS gives an approximate agreement with the abundance pattern of metal-poor weak $r$ star HD~122563, although the third-peak elements are produced only when the $\bar{\nu}_e$ energy is much larger than the $\nu_e$ energy. In the proton-rich wind, strong $\nu p$-process occurs and $A>100$ nuclides are synthesized. The synthesized nuclei can be neutron-rich in some cases because large neutrino luminosity of the massive proto-neutron star supplies sufficient amount of neutrons. In addition, we show that an interesting nucleosynthesis process would occur when the electron fraction of the wind is near 0.5. In the process, the abundance distribution of heavy-nuclei of $A>100$ achieve quasi-statistical equilibrium (QSE) at high temperature and the abundances are frozen at the end of the nucleosynthesis. This nucleosynthesis process can be understood using the ``alpha-constrained QSE" abundances we formulated. In this talk, we show an outline of these results. See more QHP seminars