Radiation-driven winds of hot luminous stars XVI. Expanding atmospheres of massive and very massive stars and the evolution of dense stellar clusters
Radiation-driven winds of hot luminous stars XVI. Expanding atmospheres of massive and very massive stars and the evolution of dense stellar clusters
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DOI：
10.1051/0004-6361/201117621
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发表时间：
2011-07
影响因子：
6.5
通讯作者：
A. Pauldrach;D. Vanbeveren;D. Vanbeveren;T. Hoffmann
中科院分区：
文献类型：
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作者：
A. Pauldrach;D. Vanbeveren;D. Vanbeveren;T. Hoffmann
语境。星暴在星系的演化中起着至关重要的作用。在这些环境中，寿命较短的大质量恒星尤其重要。大质量恒星的星风不仅对其周围环境产生重大影响，而且相关的质量损失也深刻影响恒星本身的演化。除了每颗恒星的演化外，大质量星暴星团致密核心的演化也受到N体相互作用引起的动力学过程的影响，质量高达数千个太阳质量的超大质量恒星的形成可能对星团的演化具有决定性作用。对相应观测结果的解释主要依赖于此类星暴的理论模型，这是一个重大挑战。目标。主要目标是引入一种先进的 O 型恒星大气风诊断方法，包括评估丰度、恒星和风参数测定的准确性。此外，观测结果是在我们的固定、一维线驱动风理论的框架内解释的。还讨论了由非均匀时间相关结构引起的可能影响。方法。我们将一致的大气扩张模型与关于致密星团演化的大质量和超大质量（高达数千个太阳质量）单星的恒星演化计算相结合。在这种情况下，至关重要的是大质量恒星风的精确动态参数。由于大气质量流出对辐射场和原子占据数有很大影响，而辐射场和占据数又直接影响辐射加速度，从而影响流出的强度和速度，因此流体动力结构的确定需要对膨胀大气中的统计平衡以及流体动力和辐射过程进行高度一致的处理。结果。我们提出了不同金属丰度的大质量和超大质量恒星的质量损失率、终端风速和光谱能量分布，这些数据是根据大气模型计算得出的，具有更高的一致性。这些计算对于（i）星族 III 非常大质量恒星的原始化学富集具有重要意义； (ii) 球状星团的年龄测定； (iii) 致密星团中中等质量黑洞的形成，考虑到恒星风质量损失对其祖星演化的重要性。结论。使用本文获得的超大质量恒星的质量损失率进行的恒星演化计算表明，金属丰度较低的超大质量恒星仅损失了极少量的质量；因此，非常大质量的III族恒星不太可能导致星际介质中氦气显着富集。太阳金属丰度恒星的质量损失率较高，但并没有那么高，无法排除由致密星团中的动力学过程形成的非常大的太阳金属丰度恒星结束其生命，其质量足以形成中等质量黑洞。
Context. Starbursts play an essential role in the evolution of galaxies. In these environments, massive stars, with their short lifetimes, are of particular importance. The stellar winds of massive stars significantly influence not only on their surroundings, but the associated mass loss also profoundly affects the evolution of the stars themselves. The evolution of the dense cores of massive starburst clusters is also affected by dynamical processes induced by N-body interactions, in addition to the evolution of each star, and the formation of very massive stars with masses up to several thousand solar masses may be decisive for the evolution of the cluster. The interpretation of the corresponding observations relies mainly on the theoretical modeling of such starbursts, which is a major challenge. Aims. The primary objective is to introduce an advanced diagnostic method of O-type stellar atmospheres with winds, including an assessment of the accuracy of the determinations of abundances, stellar and wind parameters. Moreover, observational results are interpreted in the framework of our stationary, one-dimensional theory of line driven winds. Possible effects caused by nonhomogeneous time dependent structures are also discussed. Methods. We combine consistent models of expanding atmospheres with stellar evolutionary calculations of massive and very massive (up to several 1000 solar masses) single stars with regard to the evolution of dense stellar clusters. Essential in this context are accurate dynamic parameters of the winds of very massive stars. Because the atmospheric mass outflow has substantial influence on the radiation field and the atomic occupation numbers, and the radiation field and the occupation numbers in turn directly influence the radiative acceleration and thus the strength and velocity of the outflow, the determination of the hydrodynamic structures requires a highly consistent treatment of the statistical equilibrium and the hydrodynamic and radiative processes in the expanding atmospheres. Results. We present computed mass loss rates, terminal wind velocities, and spectral energy distributions of massive and very massive stars of different metallicities, calculated from atmospheric models with an improved level of consistency. These computations have important implications for (i) the primordial chemical enrichment of Population III very massive stars; (ii) the age determination of globular clusters; and (iii) the formation of intermediate mass black holes in dense stellar clusters with respect to the importance of stellar wind mass loss for the evolution of their progenitor stars. Conclusions. Stellar evolutionary calculations, using the mass loss rates of very massive stars obtained in the present paper, show that very massive stars with a low metallicity lose only a very small amount of their mass; thus it is unlikely that very massive population III stars cause a significant helium enrichment of the interstellar medium. Solar-metallicity stars have higher mass-loss rates, but these are not so high to exclude very massive stars of solar metallicity, formed by dynamical processes in dense clusters, from ending their life massive enough to form intermediate-mass black holes.