PROTOSTELLAR FEEDBACK AND FINAL MASS OF THE SECOND-GENERATION PRIMORDIAL STARS
PROTOSTELLAR FEEDBACK AND FINAL MASS OF THE SECOND-GENERATION PRIMORDIAL STARS
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DOI：
10.1088/2041-8205/760/2/l37
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发表时间：
2012-10
期刊：
影响因子：
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通讯作者：
T. Hosokawa;N. Yoshida;K. Omukai;H. Yorke
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文献类型：
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作者：
T. Hosokawa;N. Yoshida;K. Omukai;H. Yorke
宇宙中的第一批恒星通过各种反馈过程电离了周围的原始气体。 “第二代”太初恒星可能由这种扰动气体重组后形成。在这封信中，我们研究了此类第二代恒星的形成晚期阶段，其中大量气体吸积到原恒星上，并且在吸积终止时确定了最终的恒星质量。我们直接计算吸积流和恒星紫外线（UV）辐射之间复杂的相互作用，进行辐射流体动力学模拟以及恒星演化计算。由于前恒星阶段的 H2 和 HD 冷却效率更高，恒星上的吸积率比第一颗恒星形成时的吸积率低 10 倍。较低的吸积速率和包络密度导致在较低的原恒星质量 M* ≃ 10 M☉ 处出现膨胀的双极 H ii 区域，从而吹灭星周物质，从而淬灭从包络到吸积盘的质量供应。与此同时，由于成长中的恒星的光蒸发，圆盘失去了质量。在我们的基准案例中，恒星紫外线反馈终止了恒星在 M* ≃ 17 M☉ 处的质量吸积。尽管第二代原初恒星的衍生质量总体上低于第一代，但差异仅在几倍之内。我们的结果提出了一种新的情况，即大多数原始恒星诞生时都是具有数十个太阳质量的大质量恒星，无论它们是哪代的。
The first stars in the universe ionized the ambient primordial gas through various feedback processes. “Second-generation” primordial stars potentially form from this disturbed gas after its recombination. In this Letter, we study the late formation stage of such second-generation stars, where a large amount of gas accretes onto the protostar and the final stellar mass is determined when the accretion terminates. We directly compute the complex interplay between the accretion flow and stellar ultraviolet (UV) radiation, performing radiation-hydrodynamic simulations coupled with stellar evolution calculations. Because of more efficient H2 and HD cooling in the pre-stellar stage, the accretion rates onto the star are 10 times lower than in the case of the formation of the first stars. The lower accretion rates and envelope density result in the occurrence of an expanding bipolar H ii region at a lower protostellar mass M* ≃ 10 M☉, which blows out the circumstellar material, thereby quenching the mass supply from the envelope to the accretion disk. At the same time the disk loses mass due to photoevaporation by the growing star. In our fiducial case the stellar UV feedback terminates mass accretion onto the star at M* ≃ 17 M☉. Although the derived masses of the second-generation primordial stars are systematically lower than those of the first generation, the difference is within a factor of only a few. Our results suggest a new scenario, whereby the majority of the primordial stars are born as massive stars with tens of solar masses, regardless of their generations.