General Relativistic Effects on Neutrino‐driven Winds from Young, Hot Neutron Stars andr‐Process Nucleosynthesis

Abstract

Neutrino-driven wind from young hot neutron star, which is formed by supernova explosion, is the most promising candidate site for r-process nucleosynthesis. We study general relativistic effects on this wind in Schwarzschild geometry in order to look for suitable conditions for a successful r-process nucleosynthesis. It is quantitatively discussed that the general relativistic effects play a significant role in increasing entropy and decreasing dynamic time scale of the neutrino-driven wind. Exploring wide parameter region which determines the expansion dynamics of the wind, we find interesting physical conditions which lead to successful r-process nucleosynthesis. The conditions which we found realize in the neutrino-driven wind with very short dynamic time scale τ dyn ∼ 6 ms and relatively low entropy S ∼ 140. We carry out the α-process and rprocess nucleosynthesis calculation on these conditions by the use of our single network code including over 3000 isotopes, and confirm quantitatively that the second and third r-process abundance peaks are produced in the neutrino-driven wind.

Astrophysical reaction rate for α(αn,γ)9Be by photodisintegration

“…The production of seed elements in the neutrino-driven wind and the alpha-rich freeze-out scenarios can be enhanced due to the slight increase of the reaction rate at T 9 > 3.5. This may lead to a slightly smaller neutron-to-seed ratio at the onset of r-process, and hence make an appreciable influence on the entropy condition and expansion dynamics of the neutrino-driven wind [4]. Kajino et al have recently studied the sensitivity of the r-process yields to the α(αn, γ) 9 Be reaction rate, and found that a factor of two larger rate would change the final r-process abundances drastically in rapid expansion models of the neutrino-driven wind [45].…”

“…In this rapid expansion, there is essentially no time for the triple alpha reaction to set in and, instead, the ααn reaction becomes again crucial for the r-process. The necessary expansion time is determined in comparison with the reaction time scale of the ααn reaction [4]. A more recent study reveals that the reaction flow can go through the neutron-rich region of light elements in the rapidly expanding wind [6,7].…”

R-process nucleosynthesis in core-collapse supernova explosion

“…Shown by white dots in Fig. 1 are the isotopes included in our reaction network [7,9]. Let us remind the readers that there were at least three difficulties in the previous theoretical studies of the r-process.…”

“…Highlight abundance scales to logY , where Y is the number fraction of each nucleus. White dots show the nuclei included in the reaction network code [7,9]. The neutrino-driven wind model used is for L ν = 10 52 ergs/s and M = 2M ⊙ [7].…”

“…Figure 2. R-process abundance [7] (solid line) as a function of atomic mass number A compared with the solar system r-process abundance (filled circles) from Käppeler, Beer, & Wisshak [10]. The neutrino-driven wind model used is for L ν = 10 52 ergs/s and M = 2M ⊙ .…”