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arXiv 1503.05197astro-ph.SR
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激变变星中的白矮星质量

White dwarf masses in cataclysmic variables

T. P. G. Wijnen, M. Zorotovic, M. R. Schreiber

摘要:

最近发现激变变星(CV)的白矮星(WD)质量分布与标准CV形成模型的预测大相径庭。CV中的高平均WD质量在当前观察到的CV祖细胞样品中没有印记,并且不能归因于选择效应。已经提出了两种可能性:无论是WD增长的CV演变过程中的质量,或在一个显着的分数的情况下,CV形成之前的热时间尺度的质量传递(TTMT)的(短)阶段,其中WD获得足够的质量。我们调查,如果这两种情况下,可以使理论预测和观察到的协议。我们采用二进制人口合成模型来模拟目前的内在CV人口。我们纳入了特定的CV演变方面,如适当的质量半径关系的捐助者的明星和更详细的处方的临界质量比动态不稳定的传质。我们还实施了以前建议的风从表面的WD在TTMT和测试的想法WD质量增长在CV阶段通过任意改变吸积效率。我们比较了模型的预测与来自观察到的样本的CV的特性。我们发现,质量增长的WD在CV未能重现所观察到的WD质量分布。在TTMT的情况下,我们能够产生大量的大规模WD,如果我们假设显着的质量损失从表面的WD在TTMT阶段。然而,该模型仍然产生太多的CV与氦WD。此外,施主星在许多这些后TTMT CV中演化,这与观测结果相矛盾。我们的结论是,在我们目前的框架CV演变TTMT也WD质量增长不能完全解释所观察到的WD质量或CV的周期分布。

英文摘要:

The white dwarf (WD) mass distribution of cataclysmic variables (CVs) has recently been found to dramatically disagree with the predictions of the standard CV formation model. The high mean WD mass among CVs is not imprinted in the currently observed sample of CV progenitors and cannot be attributed to selection effects. Two possibilities have been put forward: either the WD grows in mass during CV evolution, or in a significant fraction of cases, CV formation is preceded by a (short) phase of thermal time-scale mass transfer (TTMT) in which the WD gains a sufficient amount of mass. We investigate if either of these two scenarios can bring theoretical predictions and observations into agreement. We employed binary population synthesis models to simulate the present intrinsic CV population. We incorporated aspects specific to CV evolution such as an appropriate mass-radius relation of the donor star and a more detailed prescription for the critical mass ratio for dynamically unstable mass transfer. We also implemented a previously suggested wind from the surface of the WD during TTMT and tested the idea of WD mass growth during the CV phase by arbitrarily changing the accretion efficiency. We compare the model predictions with the characteristics of CVs derived from observed samples. We find that mass growth of the WDs in CVs fails to reproduce the observed WD mass distribution. In the case of TTMT, we are able to produce a large number of massive WDs if we assume significant mass loss from the surface of the WD during the TTMT phase. However, the model still produces too many CVs with helium WDs. Moreover, the donor stars are evolved in many of these post-TTMT CVs, which contradicts the observations. We conclude that in our current framework of CV evolution neither TTMT nor WD mass growth can fully explain either the observed WD mass or the period distribution in CVs.

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