Nuclear Reactions in the Crusts of Accreting Neutron Stars
Nuclear Reactions in the Crusts of Accreting Neutron Stars
复制标题
吸积中子星地壳中的核反应
DOI：
10.3847/1538-4357/aabfe0
复制
发表时间：
2018
期刊：
影响因子：
--
通讯作者：
Y. Xu
中科院分区：
文献类型：
--
作者：
R. Lau;R. Lau;M. Beard;M. Beard;S. Gupta;H. Schatz;H. Schatz;A. Afanasjev;E. Brown;E. Brown;Alex Deibel;Alex Deibel;L. Gasques;G. W. Hitt;W. Hix;W. Hix;L. Keek;L. Keek;P. Möller;P. Möller;P. Shternin;A. Steiner;A. Steiner;A. Steiner;M. Wiescher;M. Wiescher;Y. Xu
对静止期间瞬态吸积中子星的 X 射线观测提供了有关中子星外壳结构和致密物质特性的信息。对观测数据的解释需要了解在吸积过程中加热和冷却地壳的核反应，并定义其非平衡成分。我们在这里详细识别了典型的核反应序列，直至地壳深处，其中质量密度使用完整的核反应网络来表示一系列初始成分。反应顺序与以前的工作有很大不同。我们发现，无论初始成分如何，在向内地壳过渡时地壳杂质都会大幅减少，尽管壳效应可能会在一定程度上延迟纯地壳的形成，使其密度超过 。这自然地解释了从广泛的系统观察中推断出的小内壳杂质。例外情况是 A ≥ 102 核的初始成分，由于 N = 82 壳封闭，内壳仍然不纯，杂质参数 Qimp ≈ 20。与之前的工作一致，我们发现核加热相对稳定并且与初始成分无关，而外地壳中通过核乌尔卡循环进行的冷却在很大程度上取决于初始成分。这项工作为未来研究地壳模型对核物理的敏感性奠定了基础，并为现实地壳模型提供了成分概况。
X-ray observations of transiently accreting neutron stars during quiescence provide information about the structure of neutron star crusts and the properties of dense matter. Interpretation of the observational data requires an understanding of the nuclear reactions that heat and cool the crust during accretion and define its nonequilibrium composition. We identify here in detail the typical nuclear reaction sequences down to a depth in the inner crust where the mass density is using a full nuclear reaction network for a range of initial compositions. The reaction sequences differ substantially from previous work. We find a robust reduction of crust impurity at the transition to the inner crust regardless of initial composition, though shell effects can delay the formation of a pure crust somewhat to densities beyond . This naturally explains the small inner crust impurity inferred from observations of a broad range of systems. The exception are initial compositions with A ≥ 102 nuclei, where the inner crust remains impure with an impurity parameter of Qimp ≈ 20 owing to the N = 82 shell closure. In agreement with previous work, we find that nuclear heating is relatively robust and independent of initial composition, while cooling via nuclear Urca cycles in the outer crust depends strongly on initial composition. This work forms a basis for future studies of the sensitivity of crust models to nuclear physics and provides profiles of composition for realistic crust models.