用哈勃太空望远镜/STIS解剖的R136星团。III。最大质量的恒星和它们聚集的恒星风
The R136 star cluster dissected with Hubble Space Telescope/STIS. III. The most massive stars and their clumped winds
摘要：
大麦哲伦星系内部的星团R136拥有丰富的大质量恒星，包括已知的最大质量恒星。这些非常明亮的恒星的强烈恒星风影响着它们的演化和周围的环境。我们目前缺乏量化这种影响所需的风结构的详细知识。目的：从观测上约束R136中大质量恒星的恒星和风性质，特别是与风聚集有关的参数。研究方法：我们同时分析光学和紫外光谱的53 O型和3 WNH-星使用FASTWIND模式大气代码和遗传算法。该模型占光学厚团块和影响有关的孔隙度和速度孔隙度，以及一个非空的interclump介质。结果如下：我们获得恒星参数，表面丰度，质量损失率，终极速度和集群特性，并比较这些理论预测和演化模型。团簇性质包括团簇间介质的密度和风的速度-孔隙度。这是第一次系统地测量这些特性的有效温度和光度范围很广。结论：我们确认了星团的年龄为1.0-2.5百万年，并推导出我们样本中质量最大的恒星R136 a1的初始恒星质量为$\geq 250 {\rm M}_\odot$。我们样本恒星的风是高度聚集的，平均聚集因子为$f_{\rm cl}=29\pm15$。我们发现试探性的趋势，风结构参数作为质量损失率的函数，这表明具有较高质量损失率的恒星的风较少聚集。我们比较了几个理论预测所观察到的质量损失率和终极速度，并发现没有令人满意地再现这两个量。Krtička & Kubát（2018）的处方与观察到的质量损失率最匹配。
英文摘要：
Context: The star cluster R136 inside the LMC hosts a rich population of massive stars, including the most massive stars known. The strong stellar winds of these very luminous stars impact their evolution and the surrounding environment. We currently lack detailed knowledge of the wind structure that is needed to quantify this impact. Aims: To observationally constrain the stellar and wind properties of the massive stars in R136, in particular the parameters related to wind clumping. Methods: We simultaneously analyse optical and UV spectroscopy of 53 O-type and 3 WNh-stars using the FASTWIND model atmosphere code and a genetic algorithm. The models account for optically thick clumps and effects related to porosity and velocity-porosity, as well as a non-void interclump medium. Results: We obtain stellar parameters, surface abundances, mass-loss rates, terminal velocities and clumping characteristics and compare these to theoretical predictions and evolutionary models. The clumping properties include the density of the interclump medium and the velocity-porosity of the wind. For the first time, these characteristics are systematically measured for a wide range of effective temperatures and luminosities. Conclusions: We confirm a cluster age of 1.0-2.5 Myr and derive an initial stellar mass of $\geq 250 {\rm M}_\odot$ for the most massive star in our sample, R136a1. The winds of our sample stars are highly clumped, with an average clumping factor of $f_{\rm cl}=29\pm15$. We find tentative trends in the wind-structure parameters as a function of mass-loss rate, suggesting that the winds of stars with higher mass-loss rates are less clumped. We compare several theoretical predictions to the observed mass-loss rates and terminal velocities and find that none satisfactorily reproduces both quantities. The prescription of Krtička & Kubát (2018) matches best the observed mass-loss rates.
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