The Galactic WC and WO stars
The Galactic WC and WO stars
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DOI：
10.1051/0004-6361/201833712
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发表时间：
2018-07
影响因子：
6.5
通讯作者：
A. Sander;W. Hamann;H. Todt;R. Hainich;T. Shenar;V. Ramachandran;L. Oskinova
中科院分区：
文献类型：
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作者：
A. Sander;W. Hamann;H. Todt;R. Hainich;T. Shenar;V. Ramachandran;L. Oskinova
碳序沃尔夫-拉叶星（WC星）是大质量恒星在核心坍缩之前演化的重要基石。由于核心氦燃烧，无氢的物体有巨大的质量损失，它们可能是坍缩前最后一个可观测的阶段，因此有希望成为Ib/c型超新星的先驱候选者。它们强烈的质量损失进一步对辐射驱动风的理论提出了挑战和限制。因此，WC星星参数的确定对于许多天体物理领域都具有重要意义。有了盖亚DR 2，第一次可以获得银河系WC恒星的大样本，消除了早期研究中固有的主要不确定性。在这项工作中，我们重新审视以前研究的WC星的样本，以获得银河系WC人口的关键属性。依赖于距离的所有量都将更新，而基础光谱分析保持不变。与早期的假设相比，我们的研究得出，相同亚型的WC星在绝对星等上可以有很大的差异。有了盖亚DR 2，银河系WC人口的图像变得更加复杂：我们获得的光度范围从logL/L = 4.9-6.0与一个离群值（WR 119）具有logL/L = 4.7。这表明WC星可能是由比以前假设的更宽的初始质量范围形成的。我们得到的质量损失率在log λ = −5.1和−4.1之间，λ λ L为0.68，修正的风动量与光度成线性比例。我们讨论了恒星演化的影响，包括未解决的问题，需要的信封通货膨胀，以解决WR半径的问题，和开放的问题，WR星与伽玛射线暴的连接。WC和WO恒星是大质量黑洞的祖先，它们要么安静地坍缩，要么在超新星中坍缩，而超新星很可能在WO阶段之前发生。
Wolf-Rayet stars of the carbon sequence (WC stars) are an important cornerstone in the late evolution of massive stars before their core collapse. As core-helium burning, hydrogen-free objects with huge mass-loss, they are likely the last observable stage before collapse and thus promising progenitor candidates for type Ib/c supernovae. Their strong mass-loss furthermore provides challenges and constraints to the theory of radiatively driven winds. Thus, the determination of the WC star parameters is of major importance for several astrophysical fields. With Gaia DR2, for the first time parallaxes for a large sample of Galactic WC stars are available, removing major uncertainties inherent to earlier studies. In this work, we re-examine a previously studied sample of WC stars to derive key properties of the Galactic WC population. All quantities depending on the distance are updated, while the underlying spectral analyzes remain untouched. Contrasting earlier assumptions, our study yields that WC stars of the same subtype can significantly vary in absolute magnitude. With Gaia DR2, the picture of the Galactic WC population becomes more complex: We obtain luminosities ranging from logL/L⊙ = 4.9–6.0 with one outlier (WR 119) having logL/L⊙ = 4.7. This indicates that the WC stars are likely formed from a broader initial mass range than previously assumed. We obtain mass-loss rates ranging between log Ṁ = −5.1 and −4.1, with Ṁ ∝ L0.68 and a linear scaling of the modified wind momentum with luminosity. We discuss the implications for stellar evolution, including unsolved issues regarding the need of envelope inflation to address the WR radius problem, and the open questions in regard to the connection of WR stars with Gamma-ray bursts. WC and WO stars are progenitors of massive black holes, collapsing either silently or in a supernova that most-likely has to be preceded by a WO stage.