围绕快速旋转、化学均匀演化、可能的伽马射线暴前身的星周介质
The circumstellar medium around a rapidly rotating, chemically homogeneously evolving, possible gamma-ray burst progenitor
摘要：
快速旋转、化学成分均匀演化的大质量恒星被认为是长伽马射线暴的祖先。我们提出了一个快速旋转的20 Msol恒星周围的星周介质在Z=0.001的金属丰度的演化的数值模拟。它的旋转速度足够快，可以产生准化学均匀演化。虽然传统上，20 Msol的恒星不会演变成沃尔夫-拉叶阶段，所考虑的模型从主序直接演变成氦主序。我们使用随时间变化的风参数，如质量损失率，风速和旋转引起的风各向异性的演变模型作为输入的二维流体动力学模拟。虽然压力驱动的星周气泡的外缘是球形的，但在近临界旋转期间和之后，靠近恒星的星周介质显示出强烈的非球形特征。我们的结论是，快速旋转的大质量恒星周围的星周介质与类似质量的非旋转恒星周围的物质有很大的不同。预测了伽马射线暴余辉谱中的多重蓝移高速吸收分量。在恒星生命的最后几千年里，由于近临界旋转和短恒星演化时间尺度，我们发现极向的星周密度分布与通常与恒星附近的恒星风相关的1/R^2密度分布有很大的偏差
英文摘要：
Rapidly rotating, chemically homogeneously evolving massive stars are considered to be progenitors of long gamma-ray bursts. We present numerical simulations of the evolution of the circumstellar medium around a rapidly rotating 20 Msol star at a metallicity of Z=0.001. Its rotation is fast enough to produce quasi-chemically homogeneous evolution. While conventionally, a star of 20 Msol would not evolve into a Wolf-Rayet stage, the considered model evolves from the main sequence directly to the helium main sequence. We use the time-dependent wind parameters, such as mass loss rate, wind velocity and rotation-induced wind anisotropy from the evolution model as input for a 2D hydrodynamical simulation. While the outer edge of the pressure-driven circumstellar bubble is spherical, the circumstellar medium close to the star shows strong non-spherical features during and after the periods of near-critical rotation. We conclude that the circumstellar medium around rapidly rotating massive stars differs considerably from the surrounding material of non-rotating stars of similar mass. Multiple blue-shifted high velocity absorption components in gamma-ray burst afterglow spectra are predicted. As a consequence of near critical rotation and short stellar evolution time scales during the last few thousand years of the star's life, we find a strong deviation of the circumstellar density profile in the polar direction from the 1/R^2 density profile normally associated with stellar winds close to the star
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