arXiv 2203.133832022-03-24astro-ph.SRastro-ph.HEphysics.plasm-ph

高密度白矮星混合等离子体的精确扩散系数

Accurate Diffusion Coefficients for Dense White Dwarf Plasma Mixtures

M. E. Caplan, E. B. Bauer, I. F. Freeman

备注：: 6 pages, 4 figures, accepted for publication in MNRAS Letters
DOI：: 10.1093/mnrasl/slac032

摘要：

扩散系数是模拟白矮星演化的基本微观物理输入，因为它们影响结晶和沉积热源的相分离。计算扩散系数的现有方案在弱耦合（$Γ\ll 1$）下是准确的，但在强耦合液体状态（$1 \lesssim Γ\lesssim 200$）下它们具有大到两倍的误差。利用现代分子动力学程序，可以精确地确定选定系统中的扩散系数，其精度可达100%。在这项工作中，我们开发了一个理论上的动力定律的扩散系数的工作范围广泛的参数典型的白矮星内部。我们进行分子动力学模拟的纯系统和两个混合物，分别模拟一个典型的质量的C/O白矮星和一个更高质量的O/Ne白矮星，并解决了几个微量富中子核素的扩散系数。我们适合的纯系统的模型，并提出了一个物理动机的混合物的推广。我们表明，这种模型是准确的，大约15%相比，分子动力学的条件下，典型的白矮星的许多个别元素，是直接实施的恒星演化代码。

英文摘要：

Diffusion coefficients are essential microphysics input for modeling white dwarf evolution, as they impact phase separation at crystallization and sedimentary heat sources. Present schemes for computing diffusion coefficients are accurate at weak coupling ($Γ\ll 1$), but they have errors as large as a factor of two in the strongly coupled liquid regime ($1 \lesssim Γ\lesssim 200$). With modern molecular dynamics codes it is possible to accurately determine diffusion coefficients in select systems with percent-level precision. In this work, we develop a theoretically motivated law for diffusion coefficients which works across the wide range of parameters typical for white dwarf interiors. We perform molecular dynamics simulations of pure systems and two mixtures that respectively model a typical-mass C/O white dwarf and a higher-mass O/Ne white dwarf, and resolve diffusion coefficients for several trace neutron-rich nuclides. We fit the model to the pure systems and propose a physically motivated generalization for mixtures. We show that this model is accurate to roughly 15% when compared to molecular dynamics for many individual elements under conditions typical of white dwarfs, and is straightforward to implement in stellar evolution codes.

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英文摘要：

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