THE CHEMICAL IMPRINT OF SILICATE DUST ON THE MOST METAL-POOR STARS
THE CHEMICAL IMPRINT OF SILICATE DUST ON THE MOST METAL-POOR STARS
复制标题
最贫金属恒星上硅酸盐尘埃的化学印记
DOI：
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发表时间：
2013
期刊：
影响因子：
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通讯作者：
V. Bromm
中科院分区：
文献类型：
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作者：
A. Ji;A. Frebel;V. Bromm
我们研究了尘埃引起的气体碎片对早期宇宙中第一批低质量，金属贫乏恒星（<1 M☉）形成的影响。先前的研究表明，存在一个临界的尘气比，低于这个比，尘热冷却就不能导致气体破碎。假设第一颗尘埃是硅基的，我们计算临界尘气比和相关的临界硅丰度（[Si/H]临界）。在与原恒星盘相关的密度和温度下，我们发现标准银河系晶粒尺寸分布的临界值为[Si/H] = - 4.5±0.1，而超新星反向激波产生的较小晶粒尺寸的临界值为[Si/H] = - 5.3±0.1。其他环境的密度不足以受到尘埃冷却的影响。我们通过比较在大多数贫铁恒星（[Fe/H] < -4.0）中观察到的硅丰度来验证硅酸盐尘埃冷却理论。有几颗恒星的硅丰度低到足以排除由尘埃引起的气体碎裂和标准颗粒大小分布的可能性。此外，其中两颗恒星的硅丰度非常低，即使是颗粒大小分布受到冲击的尘埃也无法解释它们的形成。添加少量碳尘不会显著改变这些结论。此外，我们发现这些恒星要么表现出高碳低硅的丰度，要么相反。因此，硅酸盐尘埃的假设表明，在最缺乏金属的地区，最早的低质量恒星形成可能经历了两种不同的冷却途径：精细结构线冷却和尘埃冷却。这自然解释了富碳恒星和正常碳恒星在极低[铁/氢]下的存在。
We investigate the impact of dust-induced gas fragmentation on the formation of the first low-mass, metal-poor stars (<1 M☉) in the early universe. Previous work has shown the existence of a critical dust-to-gas ratio, below which dust thermal cooling cannot cause gas fragmentation. Assuming that the first dust is silicon-based, we compute critical dust-to-gas ratios and associated critical silicon abundances ([Si/H]crit). At the density and temperature associated with protostellar disks, we find that a standard Milky Way grain size distribution gives [Si/H]crit = −4.5 ± 0.1, while smaller grain sizes created in a supernova reverse shock give [Si/H]crit = −5.3 ± 0.1. Other environments are not dense enough to be influenced by dust cooling. We test the silicate dust cooling theory by comparing to silicon abundances observed in the most iron-poor stars ([Fe/H] < -4.0). Several stars have silicon abundances low enough to rule out dust-induced gas fragmentation with a standard grain size distribution. Moreover, two of these stars have such low silicon abundances that even dust with a shocked grain size distribution cannot explain their formation. Adding small amounts of carbon dust does not significantly change these conclusions. Additionally, we find that these stars exhibit either high carbon with low silicon abundances or the reverse. A silicate dust scenario thus suggests that the earliest low-mass star formation in the most metal-poor regime may have proceeded through two distinct cooling pathways: fine-structure line cooling and dust cooling. This naturally explains both the carbon-rich and carbon-normal stars at extremely low [Fe/H].
影响因子：
6.5
作者：
Zeidler, S.;Posch, T.;Wehrhan, O.
通讯作者：
Wehrhan, O.