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 0809.2826v1

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 , shortdashedline), 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

Steady State Equilibrium Condition

• If neutrinos are trapped in a system of npe-e+ gas , the following reactions can take place:

e

e

e

epn

pen

nep

ee

• Generally equilibrium condition ：

• Chemical equilibrium condition

• “cold” equilibrium npe- gas(Shapiro and Teukolsky 1983)

npe

nnepe

nep

Steady State Equilibrium Condition

enep

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)

nepe

nep 2

Ye-Fei Yuan, Phy Rev D 72, 013007 (2005)

)1()1(

)1

11()1(

)1()1(0

/)2(

/)]()[(

/)(

/)(

Tenp

TEE

TE

TE

enp

enpenpnepe

enp

npnp

ee

ee

efff

ee

efff

ffffff

CAS 2

enppen

epnnep

ee

ee

,

,

e

e

e

epn

pen

nep

CAS 2

CAS 1

An Example

• Physics condition at the surface of PNS For a typical PNS: 1.4Msolar, R~Rv~10km,

at t = 2s post bounce,T~8MeV12 g cm-3,

electron fraction Ye can be determined by),,(),,(2),,( eneeep YTYTYT

[1] Arcones et al. 2008, PhRvC, 78a 5806A[2] Thompson et al. 2001, ApJ, 562, 887

Ye

CAS1 0.063 0.065[1]

CAS2 0.031 0.03[2 ］

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

Thank you