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arXiv 1208.0158astro-ph.SRastro-ph.GA
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低金属量恒星形成云中尘埃颗粒的生长会影响贫金属低质量恒星的形成吗？

Can the Growth of Dust Grains in Low-Metallicity Star-Forming Clouds Affect the Formation of Metal-Poor Low-Mass Stars?

Takaya Nozawa, Takashi Kozasa, Ken'ichi Nomoto

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5 pages, 4 figures, 1 table, Accepted for publication in ApJ Letters
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摘要：

一颗金属丰度<4.5 × 10 ^{-5} Z_sun的低质量恒星的发现揭示了尘埃在极端贫金属恒星形成中的关键作用。在本文中，我们探讨的尘埃颗粒的增长，通过吸积的气体难熔元素在非常低的金属丰度的前星核的尘埃排放冷却引起的云碎裂的效果。利用一个简单的重力坍缩气体中的晶粒生长模型，我们证明了在金属丰度为-5 <~ [Fe，Si/H] <~-3的云中，当氢密度为~10^{10}-10 ^{14} cm^{-3}时，Fe和Si晶粒可以有效地生长。当晶粒生长超过临界金属数丰度时，若晶粒初始半径不大于1 μ m或粘附概率不大于0.01，则晶粒生长导致气云碎裂的临界金属数丰度约为A_{crit} ~ 10^{-9}-10 ^{-8}。我们发现，即使初始的尘埃与气体的质量比远低于尘埃引起的碎片所需的最小值，晶粒生长增加了尘埃质量足够高，导致气体碎片成亚太阳质量块。我们认为，只要满足临界金属丰度，晶粒长大对低至10^{-5} Z_sun的低质量恒星的形成起着重要作用.

英文摘要：

The discovery of a low-mass star with such low metallicity as < 4.5x10^{-5} Z_sun reveals the critical role of dust in the formation of extremely metal-poor stars. In this paper we explore the effect of the growth of dust grains through accretion of gaseous refractory elements in very low-metallicity pre-stellar cores on the cloud fragmentation induced by the dust emission cooling. Employing a simple model of grain growth in a gravitationally collapsing gas, we show that Fe and Si grains can grow efficiently at hydrogen densities of ~10^{10}-10^{14} cm^{-3} in the clouds with metal abundances of -5 <~ [Fe, Si/H] <~ -3. The critical metal number abundances, above which the grain growth could induce the fragmentation of the gas clouds, are estimated to be A_{crit} ~ 10^{-9}-10^{-8}, unless the initial grain radius is too large (>~ 1 um) or the sticking probability is too small (<~ 0.01). We find that even if the initial dust-to-gas mass ratio is well below the minimum value required for the dust-induced fragmentation, the grain growth increases the dust mass high enough to cause the gas fragmentation into sub-solar mass clumps. We suggest that as long as the critical metal abundance is satisfied, the grain growth could play an important role in the formation of low-mass stars with metallicity as low as 10^{-5} Z_sun.

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