Structure and evolution of low‐mass W Ursae Majoris type systems – II. With angular momentum loss
Structure and evolution of low‐mass W Ursae Majoris type systems – II. With angular momentum loss
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DOI：
10.1111/j.1365-2966.2004.08457.x
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发表时间：
2004-12
期刊：
影响因子：
--
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
在前一篇文章中，我们用Eggleton的演化程序讨论了没有角动量损失（AML）的低质量WUMa型接触双星的结构和演化。该模型表现出循环行为的边缘接触状态的热时标。每个周期的一部分时间是在接触中度过的，一部分是在半分离状态中度过的。根据观察，WUMa系统遭受AML。本文提出了由引力波辐射（GR）或磁星风（MSW）引起的具有AML的低质量接触双星模型。我们发现引力辐射不能阻止WUMa系统的循环演化，引力辐射对接触双星演化的循环行为的影响几乎可以忽略。我们还发现，W UMa系统最可能的AML机制是磁制动，并且磁制动效应可以增加循环演化的周期，并缩短在不良热接触状态下花费的时间的分数。如果WUMa星不经历周期演化，并且它们的角动量损失是由两个分量的MSW同时引起的，我们发现，与从单个恒星的观测中得出的值相比，参数$\lambda$的值应该取更大的值。这表明，在W UMa系统的AML效率可能会降低，因为在W UMa系统中的组件的对流信封中包含的质量较少的非接触星相比。如果WUMa系统以恒定速率失去角动量。角动量率约为1.6\times 10^{-9} {\rm yr^{-1}}$可以防止模型的循环行为，并且模型可以保持良好的接触，接触深度基本恒定。
In a preceding paper, using Eggleton's evolution code we have discussed the structure and evolution of low-mass W UMa type contact binaries without angular momentum loss (AML). The models exhibit cyclic behavior about a state of marginal contact on a thermal time-scale. Part of the time of each cycle is spent in contact and part in a semi-detached state. According to observations, W UMa systems suffer AML. We present the models of low-mass contact binaries with AML due to gravitational wave radiation (GR) or magnetic stellar wind (MSW) are presented. We find that gravitational radiation cannot prevent the cyclic evolution of W UMa systems, and the effect of gravitational radiation on the cyclic behavior of contact binary evolution is almost negligible. We also find that the most likely AML mechanism for W UMa systems is magnetic braking, and that magnetic braking effects can increase the period of the cyclic evolution, and shorten the fraction of the time spent in the poor thermal contact state. If W UMa stars do not undergo cyclic evolution, and their angular momentum loss is caused simultaneously by MSW of both components, we find that the value of the parameter, $\lambda$, should be taken a larger value in comparison with those derived from observations of single stars. This indicates that the AML efficiency in W UMa systems may be lowered in comparison with non-contact stars because of the less mass contained in the convective envelopes of the components in W UMa systems. If W UMa systems lose their angular momentum at a constant rate. An angular momentum rate of $\frac{{\rm dln}J}{{\rm d}t}\approx 1.6\times 10^{-9} {\rm yr^{-1}}$ can prevent the cyclic behaviour of the model, and the model can keep in good contact with an essentially constant depth of contact.