The Ages of Very Cool Hydrogen-rich White Dwarfs
The Ages of Very Cool Hydrogen-rich White Dwarfs
复制标题
非常冷的富氢白矮星的年龄
DOI：
10.1086/317235
复制
发表时间：
2000
期刊：
影响因子：
--
通讯作者：
Vanderbilt University
中科院分区：
文献类型：
--
作者：
M. Salaris;E. García–Berro;M. Hernanz;J. Isern;D. S. L. Jmu;Upc Barcelona;IEEC;Vanderbilt University
白矮星的演化本质上是一个冷却过程，主要取决于它们简并核心中存储的能量和它们包层的透明度。在这篇文章中，我们计算了碳-氧白矮星在氢气占主导地位的所有感兴趣质量范围内的精确冷却序列。为此，我们对包层的状态方程和不透明度以及简并核心的热力学量使用了最准确的可用的物理输入。我们还研究了潜热在计算的冷却序列中的作用。我们分别给出了忽略碳-氧二元混合物相分离对结晶的影响的冷却顺序，以及适当考虑这一机制时冷却时间的延迟，以便将我们的结果与其他已发表的冷却顺序进行比较，这些冷却顺序不包括对这种现象的处理。我们发现，在忽略相分离的情况下，当对数(L/L☉)=-4.5时，对于一颗典型的~0.6M☉白矮星，在纯氢气氛下非常冷的白矮星的冷却年龄被系统地低估了约1.5Gyr。如果包括二元混合物的相分离，则冷却年龄进一步增加约10%。文中还给出了几张彩色星等图中的冷却轨迹和冷却等时线。
The evolution of white dwarfs is essentially a cooling process that depends primarily on the energy stored in their degenerate cores and on the transparency of their envelopes. In this paper we compute accurate cooling sequences for carbon-oxygen white dwarfs with hydrogen dominated atmospheres for the full range of masses of interest. For this purpose we use the most accurate available physical inputs for both the equation of state and opacities of the envelope and for the thermodynamic quantities of the degenerate core. We also investigate the role of the latent heat in the computed cooling sequences. We present separately cooling sequences in which the effects of phase separation of the carbon-oxygen binary mixture upon crystallization have been neglected, and the delay introduced in the cooling times when this mechanism is properly taken into account, in order to compare our results with other published cooling sequences which do not include a treatment of this phenomenon. We find that the cooling ages of very cool white dwarfs with pure hydrogen atmospheres have been systematically underestimated by roughly 1.5 Gyr at log(L/L☉) = -4.5 for an otherwise typical ~0.6 M☉ white dwarf, when phase separation is neglected. If phase separation of the binary mixture is included, then the cooling ages are further increased by roughly 10%. Cooling tracks and cooling isochrones in several color-magnitude diagrams are presented as well.