A revision of the theory of hot-star winds

热星风理论的修正

• 批准号: 274933767
• 负责人: Professor Dr. Wolf-Rainer Hamann
• 金额: --
• 依托单位: Institut für Physik und Astronomie
• 依托单位国家: 德国
• 项目类别: Research Grants
• 财政年份: 2015
• 资助国家: 德国
• 起止时间: 2014-12-31 至 2017-12-31
• 项目状态: 已结题
• 来源: https://gepris.dfg.de/gepris/projekt/274933767?language=en
• 关键词: revision; theory; hot; star; winds

Some stars are formed with ten or even hundred times more mass than the sun. Such "massive" stars play an important role in the cosmos. Their radiation is up to million times stronger than that of the sun, and they drive a strong stellar wind by which they disperse the major part of their mass during their short lifetime. Finally they explode as supernova. The ubiquity and importance of mass loss from hot stars has been discovered almost 50 years ago. Soon after, a theory was proposed in order to explain how such huge amount of matter can de blown off. The essential mechanism is the pressure that is exerted by the enormously intense radiation of the star. The matter in the stellar wind partly absorbs this radiation and is thus accelerated. The mentioned theory of radiation-driven winds describes these very complicate processes under drastic approximations. Nevertheless, the results were in good agreement with observations, at least for those types of stars which were studied first (supergiants of spectral types O and B). From today's perspective, this good agreement was perhaps only by incidence. In the meantime, the models for analyzing the observations have been improved and now imply that the most important parameter, the mass-loss rates, have to be revised downward significantly. For other types of massive stars, the mentioned theory was not applicable anyhow, or gave wrong predictions. Various authors have already challenged one or another of the approximations on which the mentioned stellar-wind theory is based on - partly with alarming results. The detailed treatment of the radiation processes in stellar winds requires an enormous effort. However, such efforts are unavoidable for the interpretation and quantitative analysis of the spectra from hot stars with winds. The Potsdam group has developed a corresponding computer code (Potsdam Wolf-Rayet model atmospheres - PoWR). Only very few comparable codes exist worldwide. These simulations of stellar spectra can also evaluate the radiation pressure at any point in the atmosphere. On this basis, we have developed a method to model the hydrodynamics of the stellar wind consistently. The drastic approximations of the stellar wind theory mentioned above are thus avoided. Our models explain for the first time the winds of the so-called Wolf-Rayet stars, which are the strongest stellar winds observed.In the new project, these calculations shall now be applied to stellar winds in general. One needs to understand, where and why the different approximations in the schematic stellar-wind theory break down. After the new models have been checked with observations, we will perform hydrodynamic simulations for the widest variety of stars and predict their mass-loss rates. Such predictions are urgently needed in order to understand the evolution of massive stars, stellar clusters, and whole galaxies.

有些恒星的质量是太阳的十倍甚至上百倍。这种“大质量”恒星在宇宙中扮演着重要的角色。它们的辐射比太阳强一百万倍，在它们短暂的生命中，它们会驱动强烈的恒星风，从而分散它们的大部分质量。最后，它们以超新星的形式爆炸。近50年前，人们就发现了热星质量损失的普遍性和重要性。不久之后，一个理论被提出，以解释如此巨大的物质是如何被吹走的。其基本机制是恒星极强的辐射所施加的压力。恒星风中的物质部分地吸收了这种辐射，因此被加速。前面提到的辐射驱动风理论描述了在剧烈近似下这些非常复杂的过程。尽管如此，结果与观测结果是一致的，至少对于那些首先被研究的恒星类型(光谱类型O和B的超巨星)是如此。从今天的角度来看，这种良好的共识可能只是偶然的。与此同时，分析观测数据的模型得到了改进，现在意味着最重要的参数--质量损失率--必须大幅下调。对于其他类型的大质量恒星，上述理论无论如何都不适用，或者给出了错误的预测。不同的作者已经对上述恒星风理论所基于的一种或另一种近似提出了质疑--部分结果令人震惊。要详细处理恒星风中的辐射过程，需要付出巨大的努力。然而，对于解释和定量分析有风的热星的光谱，这样的努力是不可避免的。波茨坦小组开发了相应的计算机代码(波茨坦Wolf-Rayet模型大气-POWR)。世界范围内只有很少的可比代码。这些恒星光谱的模拟还可以评估大气中任何一点的辐射压力。在此基础上，我们发展了一种一致地模拟恒星风流体动力学的方法。这样就避免了上述恒星风理论的极端近似。我们的模型首次解释了所谓的Wolf-Rayet恒星的风，这是观察到的最强的恒星风。在新的项目中，这些计算现在将应用于一般的恒星风。人们需要理解，在哪里以及为什么在示意性恒星风理论中不同的近似被打破。在新模型与观测结果进行核对后，我们将对最广泛的恒星进行流体动力学模拟，并预测它们的质量损失率。为了了解大质量恒星、星团和整个星系的演化，迫切需要这样的预测。

项目成果

Driving classical Wolf-Rayet winds: A Γ- and Z-dependent mass-loss

驱动经典沃尔夫拉叶风：A 和 Z 相关的质量损失

• DOI: 10.1093/mnras/stz3064
• 发表时间: 2019
• 期刊: Monthly Notices of the Royal Astronomical Society
• 影响因子: 4.8
• 作者: Sander;A. A. C;Hamann
• 通讯作者: Hamann

The Galactic WN stars revisited

• DOI: 10.1051/0004-6361/201834850
• 发表时间: 2019-04
• 期刊: Astronomy & Astrophysics
• 影响因子: 6.5
• 作者: W. Hamann;G. Gräfener;A. Liermann;R. Hainich;A. Sander;T. Shenar;V. Ramachandran;H. Todt

The Galactic WC and WO stars

• DOI: 10.1051/0004-6361/201833712
• 发表时间: 2018-07
• 期刊: Astronomy & Astrophysics
• 影响因子: 6.5
• 作者: A. Sander;W. Hamann;H. Todt;R. Hainich;T. Shenar;V. Ramachandran;L. Oskinova

Coupling hydrodynamics with comoving frame radiative transfer - I. A unified approach for OB and WR stars

流体动力学与共动框架辐射传输的耦合 - I OB 和 WR 星的统一方法

• DOI: 10.1051/0004-6361/201730642
• 发表时间: 2017
• 期刊: Astronomy and Astrophysics
• 影响因子: 6.5
• 作者: Sander;A. A. C;Hamann;Hainich;Shenar
• 通讯作者: Shenar

Coupling hydrodynamics with comoving frame radiative transfer. II. Stellar wind stratification in the high-mass X-ray binary Vela X-1

• DOI: 10.1051/0004-6361/201731575
• 发表时间: 2017-08
• 期刊: Astronomy and Astrophysics
• 影响因子: 6.5
• 作者: A. Sander;F. Furst;P. Kretschmar;L. Oskinova;H. Todt;R. Hainich;T. Shenar;W. Hamann