The Impact of HD Cooling on the Formation of the First Stars
The Impact of HD Cooling on the Formation of the First Stars
复制标题
高清冷却对第一批恒星形成的影响
DOI：
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发表时间：
2008
期刊：
影响因子：
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通讯作者：
G. Bryan
中科院分区：
文献类型：
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作者：
I. McGreer;G. Bryan
我们使用数值模拟来研究在ΛCDM宇宙学中HD形成和冷却对第一代无金属恒星的重要性。我们已经实施和测试非平衡HD化学自适应网格细化模拟代码，并将其应用于两种情况。(1)它首先应用于在没有任何电离源的情况下形成的105-106 M的反射晕（“未扰动”晕）。我们表明，在与以前的工作，HD冷却是最晕的重要性只有边际，但是，我们发现，对于最低质量的晕，质量的几倍105 M的反，HD冷却可以等于或超过H2冷却速率。这导致了一群恒星形成于具有有效HD冷却的晕中，与H2冷却主导的晕相比，这些晕的质量要小约6倍。(2)在本文的第二部分中，我们研究了在大量自由电子存在下HD冷却的影响。这导致了较低的温度（由于电子催化产生H2），意味着产生的原恒星质量有所降低。添加HD化学物质通过将温度进一步降低到CMB的水平来改变这一点。我们发现，在102-106 cm-3的密度范围内，HD冷却比H2冷却占主导地位，但在此密度以上，温度上升，H2冷却再次占主导地位。正因为如此，原恒星的吸积速率几乎与H2的情况相同（至少对于吸积质量低于50-100 M的情况）;因此我们认为，在电离晕中HD冷却可能不会导致质量明显较低的恒星。
We use numerical simulations to investigate the importance of HD formation and cooling on the first generation of metal-free stars in a ΛCDM cosmology. We have implemented and tested non-equilibrium HD chemistry in an adaptive mesh refinement simulation code and applied it to two situations. (1) It is first applied to the formation of 105-106 M☉ halos which form in the absence of any ionizing source (“unperturbed” halos). We show, in agreement with previous work, that HD cooling is of only marginal importance for most halos; however, we find that for the lowest mass halos, with masses a few times 105 M☉, HD cooling can equal or surpass the H2 cooling rate. This leads to a population of stars formed in halos with effective HD cooling that are less massive by a factor of ~6 compared to halos dominated by H2 cooling. (2) In the second part of the paper, we ionize the halos in order to explore the impact of HD cooling in the presence of an ample population of free electrons. This leads to cooler temperatures (due to the electron-catalyzed production of H2), implying somewhat lower resulting protostellar mass. Adding HD chemistry changes this by lowering the temperature further, to the level of the CMB. We find that HD cooling dominates over H2 cooling in the density range 102-106 cm−3, but above this density, the temperature rises and H2 cooling dominates again. Because of this, the accretion rate on to the protostar is almost the same as in the H2 case (at least for accreted masses below 50-100 M☉); therefore we argue that HD cooling in ionized halos will probably not result in a population of significantly lower mass stars.