物态方程对初生中子星星风动力学的影响

Effect of equation of state on the dynamics of neutrino-driven wind from proto-neutron star

初生中子星中微子驱动的星风被认为是r-过程和p-过程发生的场所之一.基于牛顿流体动力学方程组,我们讨论了3种不同物态方程((i)严格物态方程;(ii)忽略正负电子对简并参数;(iii)忽略气体压强)对初生中子星中微子驱动星风动力学的影响.结果发现,忽略简并参数的物态方程是个很好的近似;忽略气体压强的物态方程会明显地降低星风的密度、温度,提高速度和核子熵,但电子丰度几乎不会改变.同时星风物质溢出率、动力学时标等影响核合成的重要参量都有明显的改变.对1.4M⊙的典型中子星模型,我们发现在反中微子光度为8×1051ergs1时,星风物质是富中子的,采用不同的物态方程可能使诞生的快中子俘获元素的平均质量数最大相差6;在反中微子光度为1×1051ergs1时,星风物质是富质子的,质子俘获重核的相对丰度可能相差一倍,因此考虑合适的物态方程是极为重要的.

Neutrino-driven wind from proto-neutron star is regarded as one of the occasions where r-process and p-process take place. Based on Newtonian hydrodynamics equations, we discuss the effect of three different equations of state （EOSs） （EOS-1 strict; EOS-2 ignoring the degenerate parameter; EOS-3 ignoring the gas pressure） on the dynamics and nucleosynthesis of neutrino-driven wind. We find that （1） the EOS ignoring the degenerate parameter is a good approximation; （2） the EOS ignoring the gas pressure causes the density and temperature to decrease, and the speed and entropy per baryon to increase, but the electron fraction is almost not changed. Meanwhile, some important nucleosynthesis parameters, e. g., mass outflow rate and dynamic time scale, are changed dramatically. For a typical 1.4 M proto-neutron star model, when the anti-neutrino luminosity is 8×10^51 erg s-1, the wind material is neutron-rich, and the average mass number of the r-element may vary within 6 for different EOSs; While for the anti-neutrino luminosity is 1×10^51 erg s-1, the wind is proton-rich, and the abundance of proton capture element produced by EOSIII is almost one time less than that in the other two EOSs. Therefore an appropriate EOS is very important for final product of nucleosynthesis.