The empirical metallicity dependence of the mass-loss rate of O- and early B-type stars
The empirical metallicity dependence of the mass-loss rate of O- and early B-type stars
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DOI：
10.1051/0004-6361:20077545
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发表时间：
2007-08
影响因子：
6.5
通讯作者：
M. R. Mokiem;A. D. Koter;J. Vink;J. Puls;C. Evans;S. Smartt;P. Crowther;A. Herrero;A. Herrero;N. Langer;D. Lennon;F. Najarro;M. R. Villamariz
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文献类型：
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作者：
M. R. Mokiem;A. D. Koter;J. Vink;J. Puls;C. Evans;S. Smartt;P. Crowther;A. Herrero;A. Herrero;N. Langer;D. Lennon;F. Najarro;M. R. Villamariz
我们提出了一个全面的研究的观测依赖性的质量损失率在固定恒星风的热大质量恒星的金属含量的大气。讨论了麦哲伦星云中恒星的金属含量，并对这两个卫星系统和银河系中OB星的最新质量损失测定进行了严格的评估。假设质量损失与金属含量呈幂律关系，u M <$Z m，并采用末端流速与金属含量之间的理论关系，v∞ <$Z 0.13（Leitherer等人，1992，ApJ，401，596），通过对亮度大于10 5.2 L？的恒星的风动量光度关系（WLR）的分析，我们发现非聚集外流的m = 0.83 ± 0.16。在误差范围内，该结果与Vink等人的预测值m = 0.69 ± 0.10（2001，A&A，369，574）一致。根据Hα和紫外线（UV）风线的质量损失的绝对经验值，被发现是在这个高光度制度的预测高出两个因素。如果这种差异归因于风的不均匀性，并且这种聚集并不影响预测，这意味着明亮的O型和早期B型恒星在其Hα和UV线形成区域的聚集因子约为4倍。对于光度较低的恒星，风是如此的微弱，以至于它们的强度通常不再能从光谱线（主要是Hα）中得到，目前必须依赖于紫外线的分析。我们证实，在这个低光度域中，观测到的银河系WLR比理论预期的要陡得多（尽管具体的样本相当小），导致紫外质量损失率与预测之间的差异在光度为L = 10 4.75 L？时相差100倍，其原因尚不清楚。我们强调，即使目前的热发光恒星的质量损失率会被高估的结果风聚集，但聚集的程度将是相当独立的金属丰度，在这项研究中得出的标度预计将保持正确的。
We present a comprehensive study of the observational dependence of the mass-loss rate in stationary stellar winds of hot massive stars on the metal content of their atmospheres. The metal content of stars in the Magellanic Clouds is discussed, and a critical assessment is given of state-of-the-art mass-loss determinations of OB stars in these two satellite systems and the Milky-Way. Assuming a powerlaw dependence of mass loss on metal content, u M ∝ Z m , and adopting a theoretical relation between the terminal flow velocity and metal content, v∞ ∝ Z 0.13 (Leitherer et al. 1992, ApJ, 401, 596), we find m = 0.83 ± 0.16 for non-clumped outflows from an analysis of the wind momentum luminosity relation (WLR) for stars more luminous than 10 5.2 L� . Within the errors, this result is in agreement with the prediction m = 0.69 ± 0.10 by Vink et al. (2001, A&A, 369, 574). Absolute empirical values for the mass loss, based on Hα and ultraviolet (UV) wind lines, are found to be a factor of two higher than predictions in this high luminosity regime. If this difference is attributed to inhomogeneities in the wind, and this clumping does not impact the predictions, this would imply that luminous O and early-B stars have clumping factors in their Hα and UV line forming regions of about a factor of four. For lower luminosity stars, the winds are so weak that their strengths can generally no longer be derived from optical spectral lines (essentially Hα) and one must currently rely on the analysis of UV lines. We confirm that in this low-luminosity domain the observed Galactic WLR is found to be much steeper than expected from theory (although the specific sample is rather small), leading to a discrepancy between UV mass-loss rates and the predictions by a factor 100 at luminosities of L ∼ 10 4.75 L� , the origin of which is unknown. We emphasize that even if the current mass-loss rates of hot luminous stars would turn out to be overestimated as a result of wind clumping, but the degree of clumping would be rather independent of metallicity, the scalings derived in this study are expected to remain correct.