The VLT-FLAMES Tarantula Survey XVII. Physical and wind properties of massive stars at the top of the main sequence?
The VLT-FLAMES Tarantula Survey XVII. Physical and wind properties of massive stars at the top of the main sequence?
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VLT-FLAMES 狼蛛调查 XVII。
DOI：
10.1051/0004-6361/201423643
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发表时间：
2014
影响因子：
6.5
通讯作者：
Bestenlehner J
中科院分区：
文献类型：
--
作者：
Bestenlehner J
超大质量恒星（VMS）的演化和命运与它们的质量损失性质密切相关。它们的初始质量和最终质量由于质量损失而显著不同。VMS具有强烈的恒星风和极高的电离通量，这被认为是巨氢区机械和辐射反馈的关键来源。然而，在恒星演化过程中VMS质量损失性质如何变化却知之甚少。在VLT-火焰狼蛛调查（VFTS）的框架中，我们探索了从光学薄O星星风到密度更大的WNH沃尔夫-拉叶星星风的质量损失过渡区，从而测试理论预测。为此，我们选择了62 O，Of，Of/WN和WNh恒星，这是一个前所未有的恒星样本，具有已知的最高质量和光度。我们使用非LTE辐射传输代码CMFGEN对光学VFTS以及近红外VLT/SINFONI数据进行光谱分析，以获得恒星和风参数。我们首次观测到了光学薄O星星风和光学厚富氢的WNh Wolf-Rayet风之间的转换。我们的研究结果表明，存在一个“扭结”之间的质量损失制度，与最近的Monte Carlo模拟。对于光学厚区，我们从以前的理论和观测研究中证实了对经典爱丁顿因子Γ e的陡峭依赖性。这种转变发生在主序上，亮度为106.1L，质量为80... 90米在这个极限之上，我们发现，即使考虑到中等的风聚集（fv = 0.1），相对于目前恒星演化计算中采用的标准处方，风的质量损失率也会增加。我们还表明，这导致大量的氦表面富集。最后，根据我们的光谱分析，我们能够提供迄今为止已知的最准确的VMS电离通量，证实了VMS在电离和塑造环境方面的关键作用。
The evolution and fate of very massive stars (VMS) is tightly connected to their mass-loss properties. Their initial and final masses differ significantly as a result of mass loss. VMS have strong stellar winds and extremely high ionising fluxes, which are thought to be critical sources of both mechanical and radiative feedback in giant H ii regions. However, how VMS mass-loss properties change during stellar evolution is poorly understood. In the framework of the VLT-Flames Tarantula Survey (VFTS), we explore the mass-loss transition region from optically thin O star winds to denser WNh Wolf-Rayet star winds, thereby testing theoretical predictions. To this purpose we select 62 O, Of, Of/WN, and WNh stars, an unprecedented sample of stars with the highest masses and luminosities known. We perform a spectral analysis of optical VFTS as well as near-infrared VLT/SINFONI data using the non-LTE radiative transfer code CMFGEN to obtain both stellar and wind parameters. For the first time, we observationally resolve the transition between optically thin O star winds and optically thick hydrogen-rich WNh Wolf-Rayet winds. Our results suggest the existence of a “kink” between both mass-loss regimes, in agreement with recent Monte Carlo simulations. For the optically thick regime, we confirm the steep dependence on the classical Eddington factor Γefrom previous theoretical and observational studies. The transition occurs on the main sequence near a luminosity of 106.1L⊙, or a mass of 80...90M⊙. Above this limit, we find that – even when accounting for moderate wind clumping (withfv= 0.1) – wind mass-loss rates areenhancedwith respect to standard prescriptions currently adopted in stellar evolution calculations. We also show that this results in substantial helium surface enrichment. Finally, based on our spectroscopic analyses, we are able to provide the most accurate ionising fluxes for VMS known to date, confirming the pivotal role of VMS in ionising and shaping their environments.