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arXiv 1202.4731nucl-thastro-ph.SR
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核对称能与中子星的r模不稳定性

Nuclear symmetry energy and the r-mode instability of neutron stars

Isaac Vidana

备注：
10 pages, 6 figures. Version published in Physical Review C
发表信息：
Physical Review C 85, 045808 (2012)
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摘要：

分析了对称性能量斜率参数$L$对中子星{ \it r}模不稳定性的影响。我们的研究是使用微观和唯象方法的核状态方程。微观的包括Brueckner-Hartree-Fock近似，著名的变分状态方程的Akmal，Pandharipande和Ravenhall，和最近的辅助场扩散蒙特卡罗计算的参数化。对于唯象方法，我们使用几个Skyrme力和相对论平均场模型。我们的结果表明，{ \it r}模式的不稳定性区域较小的那些模型给出较大的值的$L$。原因是体粘度（$ξ$）和剪切粘度（$η$）都随着$L$的增加而增加，因此，对于具有较大$L$的模型，模式的阻尼更有效。我们还表明，这两种粘度对$L$的依赖性可以在每个密度下由简单的幂律类型$ξ=A_ξL^{B_ξ}$和$η=A_ηL^{B_η}$来描述。使用测量的自旋频率和估计的核心温度的脉冲星的低质量X射线双星4U 1608-52，我们得出的结论是，观测数据似乎有利于值$L$大于$\sim 50$ MeV，如果这个对象被假定为不稳定区之外，它的半径是在范围$11.5-12$（$11.5-13$）公里，其质量$1.4M_\odot$（$2M_\odot$）。在这个范围之外，就不可能从这颗脉冲星得出关于$L$的任何结论。

英文摘要：

We analyze the role of the symmetry energy slope parameter $L$ on the {\it r}-mode instability of neutron stars. Our study is performed using both microscopic and phenomenological approaches of the nuclear equation of state. The microscopic ones include the Brueckner--Hartree--Fock approximation, the well known variational equation of state of Akmal, Pandharipande and Ravenhall, and a parametrization of recent Auxiliary Field Diffusion Monte Carlo calculations. For the phenomenological approaches, we use several Skyrme forces and relativisic mean field models. Our results show that the {\it r}-mode instability region is smaller for those models which give larger values of $L$. The reason is that both bulk ($ξ$) and shear ($η$) viscosities increase with $L$ and, therefore, the damping of the mode is more efficient for the models with larger $L$. We show also that the dependence of both viscosities on $L$ can be described at each density by simple power-laws of the type $ξ=A_ξL^{B_ξ}$ and $η=A_ηL^{B_η}$. Using the measured spin frequency and the estimated core temperature of the pulsar in the low-mass X-ray binary 4U 1608-52, we conclude that observational data seem to favor values of $L$ larger than $\sim 50$ MeV if this object is assumed to be outside the instability region, its radius is in the range $11.5-12$($11.5-13$) km, and its mass $1.4M_\odot$($2M_\odot$). Outside this range it is not possible to draw any conclusion on $L$ from this pulsar.

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