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arXiv 1010.0638astro-ph.SR
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在一个共同包层开始时的主星的质量和包层binding energies

Masses and envelope binding energies of primary stars at the onset of a common envelope

Marc van der Sluys, Michael Politano, Ronald E. Taam

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6 pages, 3 figures, 1 table; to be published in the proceedings of the conference "Binary Star Evolution", in Mykonos, Greece, held in June 22-25, 2010
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摘要：

我们提出的基本性质的主要恒星，启动一个共同的信封（CE）在一个二进制，而在巨大的分支。我们使用Politano et al.（2010）中描述的星群合成代码，跟踪双星星群的演化，直到主星填满其洛希叶并启动CE。然后，我们收集每个系统的属性，特别是供体的质量和结合能的供体的信封，这是很重要的CE的治疗。我们发现，对于大多数CE，施主质量是足够低的定义的核心信封边界合理。我们计算的结合能的结构参数{λ_ \mathrm{env} }和比较其分布的典型假设，在人口合成代码。我们的结论是：{λ_ \mathrm{env} }变化很小，假定该参数为一个常数，其典型误差为20- 50%.另外，这样的假设很可能导致CE参数{α_ \mathrm{CE} }的非预期和/或非物理值的隐式假设。最后，我们讨论了精确的包络结合能的现有解析拟合，这使得{λ_ \mathrm{env} }的这些过于简化的假设，以及{λ_ \mathrm{env} }的使用通常是不必要的。

英文摘要：

We present basic properties of primary stars that initiate a common envelope (CE) in a binary, while on the giant branch. We use the population-synthesis code described in Politano et al. (2010) and follow the evolution of a population of binary stars up to the point where the primary fills its Roche lobe and initiates a CE. We then collect the properties of each system, in particular the donor mass and the binding energy of the donor's envelope, which are important for the treatment of a CE. We find that for most CEs, the donor mass is sufficiently low to define the core-envelope boundary reasonably well. We compute the envelope-structure parameter {λ_\mathrm{env}} from the binding energy and compare its distribution to typical assumptions that are made in population-synthesis codes. We conclude that {λ_\mathrm{env}} varies appreciably and that the assumption of a constant value for this parameter results in typical errors of 20--50%. In addition, such an assumption may well result in the implicit assumption of unintended and/or unphysical values for the CE parameter {α_\mathrm{CE}}. Finally, we discuss accurate existing analytic fits for the envelope binding energy, which make these oversimplified assumptions for {λ_\mathrm{env}}, and the use of {λ_\mathrm{env}} in general, unnecessary.

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