1. 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

2. Introduction • The site for r-process 1. The neutron star mergers 2. The neutrino-driven wind of PNS ... Yong-Zhong Qian, astro-ph 0809.2826v1

3. Sketch of Neutrino-driven Wind G. Martınez-Pinedo, Eur. Phys. J. Special Topics 156, 123–149 (2008)

4. 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, ApJ, 562, 887

5. Steady State Equilibrium Condition • If neutrinos are trapped in a system of npe-e+ gas , the following reactions can take place:

6. Steady State Equilibrium Condition • Generally equilibrium condition ： • Chemical equilibrium condition • “cold”  equilibrium npe- gas (Shapiro and Teukolsky 1983) CAS 1

7. 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)

8. CAS 2 CAS 1

9. An Example • Physics condition at the surface of PNS For a typical PNS: 1.4Msolar, R~Rv~10km, at t = 2s post bounce,T~8MeV, r ~1012 g cm-3, electron fraction Ye can be determined by [1] Arcones et al. 2008, PhRvC, 78a 5806A [2] Thompson et al. 2001, ApJ, 562, 887

10. Discussion Due to the difference from CAS1 and CAS2, • initial electron fraction for r-process nucleosynthesis will be changed; • the position of r-process nucleosynthesis may be influenced. Wanajo S. et al., 2009, ApJ, 695, 208

11. Thank you