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arXiv 0801.4273astro-ph
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论风发射对OB超巨星光学连续谱的重要性

On the importance of the wind emission to the optical continuum of OB supergiants

Michaela Kraus, Jiri Kubat, Jiri Krticka

摘要:

以自由-自由和自由束缚形式的热风辐射,已知会出现在高温和大质量恒星的红外线和射电连续谱中。对于具有中等质量损失率和β= 0.8的风速分布的OB超巨星,1.0,预期风对光学连续谱没有影响,即λ< 1微米。然而,过去几年对OB超巨星的恒星和风参数的研究表明,对于许多物体来说,β远高于1.0,最高可达3.5。我们研究了风速分布β> 1的OB超巨星的自由-自由和自由束缚辐射对出射辐射的影响,特别是在可见光波段。对于球对称的情况下,等温风在当地的热平衡(LTE),我们计算的自由-自由和自由约束的过程和新兴的风和总的连续谱。我们对光学风连续谱的产生区域进行了局部化,并着重讨论了β> 1的β型风速分布对光学风连续谱形成的影响。发现光学风连续谱产生于约2 R * 的区域,这正是β对密度分布影响最大的风区。我们发现,当β> 1时,一个典型的OB超巨星的连续谱确实会被热风辐射污染,即使是在可见光波段。光学风辐射的强烈增加主要由自由束缚过程产生。

英文摘要:

Thermal wind emission in the form of free-free and free-bound emission is known to show up in the infrared and radio continuum of hot and massive stars. For OB supergiants with moderate mass loss rates and a wind velocity distribution with β= 0.8...1.0, no influence of the wind to the optical continuum, i.e. for λ< 1 micron, is expected. Investigations of stellar and wind parameters of OB supergiants over the last few years suggest, however, that for many objects βis much higher than 1.0, reaching values up to 3.5. We investigate the influence of the free-free and free-bound emission on the emerging radiation, especially at optical wavelengths, from OB supergiants having wind velocity distributions with β> 1. For the case of a spherically symmetric, isothermal wind in local thermodynamical equilibrium (LTE) we calculate the free-free and free-bound processes and the emerging wind and total continuum spectra. We localize the generation region of the optical wind continuum and especially focus on the influence of a β-type wind velocity distribution with β> 1 on the formation of the wind continuum at optical wavelengths. The optical wind continuum is found to be generated within about 2 R_* which is exactly the wind region where βstrongly influences the density distribution. We find that for β> 1, the continuum of a typical OB supergiant can indeed be contaminated with thermal wind emission, even at optical wavelengths. The strong increase in the optical wind emission is dominantly produced by free-bound processes.

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