The Galactic WN stars revisited
The Galactic WN stars revisited
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DOI：
10.1051/0004-6361/201834850
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发表时间：
2019-04
影响因子：
6.5
通讯作者：
W. Hamann;G. Gräfener;A. Liermann;R. Hainich;A. Sander;T. Shenar;V. Ramachandran;H. Todt;
中科院分区：
文献类型：
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作者：
W. Hamann;G. Gräfener;A. Liermann;R. Hainich;A. Sander;T. Shenar;V. Ramachandran;H. Todt;
在之前的一篇论文中，已经对银河中氮序列（即WN亚类）的Wolf-Rayet恒星进行了全面的光谱分析。然而，人们对这些天体的距离知之甚少。距离对“绝对”参数有直接影响，如光度和质量损失率。最近的盖亚数据发布（DR2）的三角视差包括我们银河系样本中几乎所有的WN恒星。在本文中，我们将新的距离应用于先前分析的银河系WN恒星，并相应地重新调整结果。在此基础上，我们提出了一份包含55颗银河系WN恒星及其恒星和风参数的修订表。质量损失率和光度之间的相关性显示出很大的散射，无论是对于无氢的WN恒星，还是对于那些可探测到氢的WN恒星。log L−log Ṁ相关性的斜率比之前发现的要浅。经验赫茨普龙-罗素图（HRD）仍然显示了先前建立的二分类，即位于零年龄主序列（ZAMS）热侧的无氢早期WN亚型和位于零年龄主序列（ZAMS）热侧的晚期WN亚型，后者显示氢并且大部分存在于比ZAMS更低的温度（少数例外）。然而，随着新的距离，恒星光度的分布比以前得到的更加连续。显示氢的晚期WN亚型恒星通常比不含氢的早期亚型恒星更亮，但是这两个亚型的光度范围是重叠的。银河系单颗WN恒星的经验HRD与最近的演化轨迹进行了比较。无论是单星演化模型还是双星方案，都不能对这些天体的参数和它们在HRD中的位置提供一个完全令人满意的解释。
Comprehensive spectral analyses of the Galactic Wolf-Rayet stars of the nitrogen sequence (i.e. the WN subclass) have been performed in a previous paper. However, the distances of these objects were poorly known. Distances have a direct impact on the “absolute” parameters, such as luminosities and mass-loss rates. The recent Gaia Data Release (DR2) of trigonometric parallaxes includes nearly all WN stars of our Galactic sample. In the present paper, we apply the new distances to the previously analyzed Galactic WN stars and rescale the results accordingly. On this basis, we present a revised catalog of 55 Galactic WN stars with their stellar and wind parameters. The correlations between mass-loss rate and luminosity show a large scatter, for the hydrogen-free WN stars as well as for those with detectable hydrogen. The slopes of the log L − log Ṁ correlations are shallower than found previously. The empirical Hertzsprung–Russell diagram (HRD) still shows the previously established dichotomy between the hydrogen-free early WN subtypes that are located on the hot side of the zero-age main sequence (ZAMS), and the late WN subtypes, which show hydrogen and reside mostly at cooler temperatures than the ZAMS (with few exceptions). However, with the new distances, the distribution of stellar luminosities became more continuous than obtained previously. The hydrogen-showing stars of late WN subtype are still found to be typically more luminous than the hydrogen-free early subtypes, but there is a range of luminosities where both subclasses overlap. The empirical HRD of the Galactic single WN stars is compared with recent evolutionary tracks. Neither these single-star evolutionary models nor binary scenarios can provide a fully satisfactory explanation for the parameters of these objects and their location in the HRD.