The origin of subdwarf B stars – I. The formation channels
The origin of subdwarf B stars – I. The formation channels
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DOI：
10.1046/j.1365-8711.2002.05752.x
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发表时间：
2002-06
影响因子：
4.8
通讯作者：
Zhanwen Han;P. Podsiadlowski;P. Maxted;T. Marsh;N. Ivanova
中科院分区：
文献类型：
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作者：
Zhanwen Han;P. Podsiadlowski;P. Maxted;T. Marsh;N. Ivanova
亚矮星B（sdB）星（以及相关的sdO/sdOB星）被认为是核心燃烧氦的天体，具有非常薄的富氢外壳。近年来，观测调查越来越清楚地表明，这些天体中有很大一部分是双星系统的成员。为了更好地理解它们的形成，我们提出了详细的调查结果的三个主要的二进制演变通道，可以导致sdB星的形成：共同的信封（CE）喷射通道，稳定的罗氏瓣溢出（RLOF）通道，和双氦白色矮星（WD）合并通道。CE喷射通道导致短周期双星中sdB星的形成，其典型的轨道周期在0.1到10 d之间，非常薄的富氢包层和质量分布在类似于0.46 M-.的附近急剧峰值。另一方面，假设所有的质量转移很快就失去了，稳定的RLOF通道产生sdB星与类似的质量，但长的轨道周期（400-1500 d）和相当厚的富氢信封。合并通道产生了单一的sdB星，它们的富氢包层非常薄，但质量分布相当广泛（0.4-0.65 M-）。我们得到的条件，从每个这些通道使用详细的恒星和二进制的演变计算，我们模拟详细的演变sdB星，并进行了简化的二进制人口合成模拟的sdB星的形成。观测到的致密双星中sdB星的周期分布强烈地限制了CE抛射参数。最适合的观测获得非常有效的CE喷射的信封电离能，与以前的结果一致。给出了sdB星在T（eff）-log g图、Hertzsprung-Russell图和质量函数分布中的分布。
Subdwarf B (sdB) stars (and related sdO/sdOB stars) are believed to be helium-core-burning objects with very thin hydrogen-rich envelopes. In recent years it has become increasingly clear from observational surveys that a large fraction of these objects are members of binary systems. To understand their formation better, we present the results of a detailed investigation of the three main binary evolution channels that can lead to the formation of sdB stars: the common-envelope (CE) ejection channel, the stable Roche lobe overflow (RLOF) channel, and the double helium white dwarfs (WDs) merger channel. The CE ejection channel leads to the formation of sdB stars in short-period binaries with typical orbital periods between 0.1 and 10 d, very thin hydrogen-rich envelopes and a mass distribution sharply peaked around similar to0.46 M-.. On the other hand, under the assumption that all mass transferred is soon lost, the stable RLOF channel produces sdB stars with similar masses but long orbital periods (400-1500 d) and with rather thick hydrogen-rich envelopes. The merger channel gives rise to single sdB stars whose hydrogen-rich envelopes are extremely thin but which have a fairly wide distribution of masses (0.4-0.65 M-.). We obtained the conditions for the formation of sdB stars from each of these channels using detailed stellar and binary evolution calculations where we modelled the detailed evolution of sdB stars and carried out simplified binary population synthesis simulations. The observed period distribution of sdB stars in compact binaries strongly constrains the CE ejection parameters. The best fits to the observations are obtained for very efficient CE ejection where the envelope ionization energy is included, consistent with previous results. We also present the distribution of sdB stars in the T (eff) -log g diagram, the Hertzsprung-Russell diagram and the distribution of mass functions.