Structure and evolution of low‐mass W UMa‐type systems
Structure and evolution of low‐mass W UMa‐type systems
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DOI：
10.1111/j.1365-2966.2004.07761.x
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发表时间：
2004-03
影响因子：
4.8
通讯作者：
Lifang Li;Zhanwen Han;Fenghui Zhang
中科院分区：
文献类型：
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作者：
Lifang Li;Zhanwen Han;Fenghui Zhang
本文用Eggleton的恒星演化程序（Eggleton 1971，1972，1973）讨论了低质量WUMa型接触双星的结构和演化。假设这些系统完全满足Roche几何，对于各种质量比（0.02 - 1.0）的接触双星，我们计算了不同接触深度的内、外Roche瓣中两个双星的相对半径（R1，2/A，R1，2为双星半径，A为轨道间距）。我们得到了一个接触双星的半径网格，在跟踪接触双星的演化过程中，利用这个半径网格，可以通过插值确定两个成分的表面位于一个等势面上。严重的不确定性主要涉及这些系统中的能量转移，即，目前还不清楚能量是如何转移的以及转移到哪里。我们假设能量转移发生在共同包层的不同区域，以研究能量转移区域对接触双星结构和演化的影响。我们发现能量转移区域对接触双星的结构和演化有着重要的影响，并得出结论：对于W型系统，能量转移可能发生在共同对流包层的最外层，而对于A型系统，能量转移发生在共同对流包层的更深层.同时，如果我们假设能量转移发生在我们的低总质量模型的最外层，并且发现我们的模型稳定地向具有较小质量比和更深包层的系统演化，这表明一些低总质量的A-型WUMa系统可以被认为是W-亚型系统的后期演化阶段，在主星迅速膨胀或主星迅速收缩期间，主星的表面温度高于主星的表面温度，这表明W亚型系统可能是由主星的膨胀或主星的收缩引起的。
The structure and evolution of low-mass W UMa type contact binaries are discussed by employing Eggleton’s stellar evolution code (Eggleton 1971, 1972, 1973). Assuming that these systems completely satisfy Roche geometry, for contact binaries with every kind of mass ratios (0.02�1.0), we calculate the relative radii (R1,2/A, where R1,2 are the radii of both stars, and A the orbital separation) of both components of contact binaries in different contact depth between inner and outer Roche lobes. We obtain a radius grid of contact binaries, and can ensure the surfaces of two components lying on an equipotential surface by interpolation using this radius grid when we follow the evolution of the contact binaries. Serious uncertainties concern mainly the transfer of energy in these systems, i.e., it is unclear that how and where the energy is transferred. We assume that the energy transfer takes place in the different regions of the common envelope to investigate the effects of the region of energy transfer on the structure and evolution of contact binaries. We find that the region of energy transfer has significant influence on the structure and evolution of contact binaries, and conclude that the energy transfer may occur in the outermost layers of the common convective envelope for W-type systems, and this transfer takes place in the deeper layers of the common envelope for A-type systems. Meanwhile, if we assume that the energy transfer takes place in the outermost layers for our model with low total mass, and find that our model steadily evolves towards a system with a smaller mass ratio and a deeper envelope, suggesting that some A-type W UMa systems with low total mass could be considered as the later evolutionary stages of W-subtype systems, and that the surface temperature of the secondary excesses that of the primary during the time when the primary expands rapidly, or the secondary contracts rapidly, suggesting that W-subtype systems may be caused by expansion of the primary, or by the contraction of the secondary.