Coupling hydrodynamics with comoving frame radiative transfer. II. Stellar wind stratification in the high-mass X-ray binary Vela X-1
Coupling hydrodynamics with comoving frame radiative transfer. II. Stellar wind stratification in the high-mass X-ray binary Vela X-1
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DOI：
10.1051/0004-6361/201731575
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发表时间：
2017-08
影响因子：
6.5
通讯作者：
A. Sander;F. Furst;P. Kretschmar;L. Oskinova;H. Todt;R. Hainich;T. Shenar;W. Hamann
中科院分区：
文献类型：
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作者：
A. Sander;F. Furst;P. Kretschmar;L. Oskinova;H. Todt;R. Hainich;T. Shenar;W. Hamann
上下文船帆座X-1是一个原型的高质量X射线双星（HMXB），它的一颗中子星星（NS）围绕着一颗早期B超巨星施主星星运行。施主星星的风在NS上的吸积为其强大的X射线亮度提供了动力。为了了解HMXBs的物理学，需要有关供体星星风的详细知识。目标。为了获得船帆座X-1中施主星星的真实图像，我们构建了一个流体动力学一致的大气模型，该模型描述了风层结，同时适当地再现了观测到的施主光谱。为了研究X射线照明如何影响恒星风，我们计算了不同X射线光度制度的其他模型。方法.我们使用最近更新的版本的波茨坦沃尔夫-拉叶代码一致地解决流体力学方程与统计方程和辐射传输。结果船帆座X-1中的风由各种元素的离子驱动，Fe iii和S iii在外部风中领先。模型预测的质量损失率与早期的经验研究一致。质量损失率几乎不受风中存在的吸积NS的影响。终端风速确定为v ∞ <$600 km s −1。另一方面，NS所在的内部区域的风速仅为100 km s-1，这在标准β速度定律的基础上是不可能的。在X射线水平增强的模型中，外部风的速度场可以改变。如果X射线通量太高，加速就会因为电离增加而中断。结论.考虑到辐射流体动力学，我们的Vela X-1施主大气模型揭示了NS位置的低风速，并提供了这一重要HMXB中风驱动的定量信息。
Context. Vela X-1, a prototypical high-mass X-ray binary (HMXB), hosts a neutron star (NS) in a close orbit around an early-B supergiant donor star. Accretion of the donor star’s wind onto the NS powers its strong X-ray luminosity. To understand the physics of HMXBs, detailed knowledge about the donor star winds is required. Aims. To gain a realistic picture of the donor star in Vela X-1, we constructed a hydrodynamically consistent atmosphere model describing the wind stratification while properly reproducing the observed donor spectrum. To investigate how X-ray illumination affects the stellar wind, we calculated additional models for different X-ray luminosity regimes. Methods. We used the recently updated version of the Potsdam Wolf–Rayet code to consistently solve the hydrodynamic equation together with the statistical equations and the radiative transfer. Results. The wind flow in Vela X-1 is driven by ions from various elements, with Fe iii and S iii leading in the outer wind. The model-predicted mass-loss rate is in line with earlier empirical studies. The mass-loss rate is almost unaffected by the presence of the accreting NS in the wind. The terminal wind velocity is confirmed at v ∞ ≈ 600 km s −1 . On the other hand, the wind velocity in the inner region where the NS is located is only ≈100 km s −1 , which is not expected on the basis of a standard β -velocity law. In models with an enhanced level of X-rays, the velocity field in the outer wind can be altered. If the X-ray flux is too high, the acceleration breaks down because the ionization increases. Conclusions. Accounting for radiation hydrodynamics, our Vela X-1 donor atmosphere model reveals a low wind speed at the NS location, and it provides quantitative information on wind driving in this important HMXB.