次级星族III星的形成判据和质量
Formation Criteria and the Mass of Secondary Population III Stars
摘要：
我们探讨了辐射流体动力学（RHD）反馈下形成的第二人口III（Pop III）恒星的形成由一个预先形成的大质量恒星。为了正确处理RHD反馈，我们进行了三维RHD模拟，包括电离光子的辐射转移以及H_2解离光子从一个预制的恒星。一个坍缩的气体云被安置在一个给定的距离从120 Msun Pop III星，云的演变是追求包括RHD反馈。我们导出了与距离有关的阈值密度，在阈值密度以上，由于H_2离解辐射的屏蔽，云可以继续坍缩。我们发现在电离锋前形成的H_2壳层能有效地屏蔽H_2的离解辐射，从而为次级Pop III星的形成提供正反馈。此外，在阈值密度附近，与电离锋相关的激波显著地剥离了气体云的包层。通过比较质量吸积时间尺度与开尔文-亥姆霍兹时间尺度，我们估计了次级Pop III星的质量。事实证明，激波的剥离可以将次级Pop III恒星的质量降低到\approx 20 Msum。
英文摘要：
We explore the formation of secondary Population III (Pop III) stars under radiation hydrodynamic (RHD) feedback by a preformed massive star. To properly treat RHD feedback, we perform three-dimensional RHD simulations incorporating the radiative transfer of ionizing photons as well as H_2 dissociating photons from a preformed star. A collapsing gas cloud is settled at a given distance from a 120Msun Pop III star, and the evolution of the cloud is pursued including RHD feedback. We derive the threshold density depending on the distance, above which the cloud can keep collapsing owing to the shielding of H_2 dissociating radiation. We find that an H_2 shell formed ahead of an ionizing front works effectively to shield the H_2 dissociating radiation, leading to the positive feedback for the secondary Pop III star formation. Also, near the threshold density, the envelope of gas cloud is stripped significantly by a shock associated with an ionizing front. By comparing the mass accretion timescale with the Kelvin-Helmholtz timescale, we estimate the mass of secondary Pop III stars. It turns out that the stripping by a shock can reduce the mass of secondary Pop III stars down to \approx 20Msum.
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