arXiv 1602.063582016-02astro-ph.SR

氦星：对沃尔夫-拉叶演化的理解

Helium Stars: Towards an Understanding of Wolf-Rayet Evolution

L. A. S. McClelland, J. J. Eldridge

备注：: 16 pages, 13 figures, 1 Table. Accepted for publication in MNRAS
DOI：: 10.1093/mnras/stw618

摘要：

沃尔夫-拉叶星（WR）是大质量恒星，通过强大的恒星风失去了大部分或全部的氢。最近的观测表明，无氢WR星的温度比目前进化模型预测的要低。为了研究不同的质量损失率如何影响WR演化，我们创建了一个纯氦星模型网格。我们将我们的结果与银河系和LMC WR观测结果进行了比较，结果表明，观察到的WR星的温度范围可以通过改变质量损失率来重现，这有效地决定了核心周围氦包层的大小。我们还发现，WN和WO星来自更大质量的恒星，而WC星来自较低的质量。这与WN和WC恒星在年龄序列中演化的标准孔蒂方案相矛盾。我们还预测了我们的模型在核心坍缩的幅度，并与附近的Ib/c型超新星的祖先的观察比较。我们证实了以前的研究结果，表明WR星是核心坍缩超新星的祖先：祖先将保持未观察到的情况下，除了在祖先是一个低质量的氦巨星，如iPTF 13 bvn的情况。

英文摘要：

Wolf-Rayet (WR) stars are massive stars that have lost most or all of their hydrogen via powerful stellar winds. Recent observations have indicated that hydrogen-free WR stars have cooler temperatures than those predicted by current evolutionary models. To investigate how varying mass-loss rate affects WR evolution, we have created a grid of pure helium star models. We compare our results with Galactic and LMC WR observations and show that the temperature ranges of observed WR stars can be reproduced by varying the mass-loss rate, which effectively determines the size of the helium envelope around the core. We also find that WN and WO stars arise from more massive stars, whereas WC stars come from lower masses. This contradicts the standard Conti scenario by which WN and WC stars evolve in an age sequence. We also predict the magnitudes of our models at core-collapse and compare with observations of nearby progenitors of Type Ib/c supernovae. We confirm the findings of previous studies that suggest WR stars are the progenitors of core-collapse supernovae: the progenitors would remain unobserved except in the cases where the progenitor is a low-mass helium giant, as is the case of iPTF13bvn.

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