The Implication of Electron-Positron Steady State Equilibrium Condition for the R-process in the Neutrino-driven Wind Liu Men-Quan Center for astrophysics, USTC
Introduction • The site for r-process 1. The neutron star mergers 2. The neutrino-driven wind of PNS. . . Yong-Zhong Qian, astro-ph 0809. 2826 v 1
Sketch of Neutrino-driven Wind G. Martınez-Pinedo, Eur. Phys. J. Special Topics 156, 123– 149 (2008)
Electron fraction (Ye, solid line), proton fraction (Xp , shortdashed line), neutron fraction (Xn, long-dashed line), and a fraction (Xa, dot-dashed line) for the highest luminosity wind model. Thompson T. A. , Burrows A. , Meyer B. S. , 2001, Ap. J, 562, 887
Steady State Equilibrium Condition • If neutrinos are trapped in a system of npe-e+ gas , the following reactions can take place:
Steady State Equilibrium Condition • Generally equilibrium condition ： • Chemical equilibrium condition • “cold” equilibrium npe- gas (Shapiro and Teukolsky 1983) CAS 1
Steady State Equilibrium Condition • If neutrinos can escape freely in a system of npe-e+ gas (i. e “hot” equilibrium npe-e+ gas) CAS 2 Ye-Fei Yuan, Phy Rev D 72, 013007 (2005)
CAS 2 CAS 1
An Example • Physics condition at the surface of PNS For a typical PNS: 1. 4 Msolar, R~Rv~10 km, at t = 2 s post bounce, T~8 Me. V, r ~1012 g cm-3, electron fraction Ye can be determined by Ye CAS 1 0. 063 0. 065[1] CAS 2 0. 031 0. 03[2］ [1] Arcones et al. 2008, Ph. Rv. C, 78 a 5806 A [2] Thompson et al. 2001, Ap. J, 562, 887
Discussion Due to the difference from CAS 1 and CAS 2, • initial electron fraction for r-process nucleosynthesis will be changed; Wanajo S. et al. , 2009, Ap. J, 695, 208 • the position of r-process nucleosynthesis may be influenced.
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