On the Mass of Population III Stars
On the Mass of Population III Stars
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论人口 III 星的质量
DOI：
10.1086/307020
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发表时间：
1998
期刊：
影响因子：
--
通讯作者：
M. Umemura
中科院分区：
文献类型：
--
作者：
F. Nakamura;M. Umemura
执行一维流体动力学计算加上氢分子形成的非平衡过程，我们追求的热量和动力学演化的原始气体云，并试图作出估计的人口III恒星的质量。云的演变计算从中央质子密度nc~102-104 cm-3到~1013 cm-3。结果表明，由于H_2冷却，对流云几乎不依赖于初始条件，继续近似等温地坍缩，直到相对于H_2线（nc~1010-1011 cm ~（-3）），云变得光学厚。在崩溃过程中，云结构分为两部分，即，一个致密的纺锤体和一个弥散的包膜。纺锤体准静态收缩，因此纺锤体的线质量保持一个仅由温度（~800 K）决定的特征值，在nc~105 cm-3到1013 cm-3的收缩过程中，该特征值为~1×103 M π pc-1。应用线性理论，我们发现，主轴是不稳定的崩溃过程中的碎片。增长最快的扰动的波长（λm）随着坍缩的进行而减小。因此，可能出现连续的碎裂。当中心密度超过nc~1010-1011 cm ~（-3）时，由于云对H_2线变得不透明，坍缩明显减速，连续的碎裂可能停止。因此，λm的最小值估计为~2×10−3 pc。第一颗星星的质量通常为3 M，通过吸积扩散的包层可能会增加到16 M。因此，第一代恒星预计是大质量的，但不是超大质量的。
Performing one-dimensional hydrodynamical calculations coupled with nonequilibrium processes for hydrogen molecule formation, we pursue the thermal and dynamical evolution of filamentary primordial gas clouds and attempt to make an estimate on the mass of Population III stars. The cloud evolution is computed from the central proton density nc~102-104 cm-3 up to ~1013 cm-3. It is found that, almost independent of initial conditions, a filamentary cloud continues to collapse nearly isothermally owing to H2 cooling until the cloud becomes optically thick against the H2 lines (nc~1010-1011 cm-3). During the collapse the cloud structure separates into two parts, i.e., a denser spindle and a diffuse envelope. The spindle contracts quasi-statically, and thus the line mass of the spindle keeps a characteristic value determined solely by the temperature (~800 K), which is ~1×103 M☉ pc-1 during the contraction from nc~105 cm-3 to 1013 cm-3. Applying a linear theory, we find that the spindle is unstable against fragmentation during the collapse. The wavelength of the fastest growing perturbation (λm) lessens as the collapse proceeds. Consequently, successive fragmentation could occur. When the central density exceeds nc~1010-1011 cm-3, the successive fragmentation may cease, since the cloud becomes opaque against the H2 lines and the collapse decelerates appreciably. Resultantly, the minimum value of λm is estimated to be ~2×10−3 pc. The mass of the first star is then expected to be typically ~3 M☉, which may grow up to ~16 M☉ by accreting the diffuse envelope. Thus, the first-generation stars are anticipated to be massive but not supermassive.