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arXiv 1402.4765astro-ph.GA
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气相中元素的贫化:粉尘成分指南

Depletions of Elements from the Gas Phase: A Guide on Dust Compositions

Edward B. Jenkins

摘要:

自20世纪70年代以来,轨道天文台记录的恒星紫外光谱揭示了我们银河系中性ISM中原子在其有利的电离阶段产生的吸收特征。大多数元素相对于氢的丰度低于它们在恒星中的值,这表明它们通过冷凝成固体形式而被去除。这些损耗的相对量因地而异,不同元素的损耗程度也各不相同。Jenkins(2009)在一项研究中,对100多篇论文中报道的243条不同视线的丰度进行了研究,描述了17种不同元素消耗的系统模式,这些结果反过来又被用来帮助我们了解尘埃颗粒的组成。由于这些结论是基于沿不同视线的差异贫化,因此它们对所采用的总元素丰度值的误差不敏感。从这项研究中得出的一些更显着的结论是:(1)在气体密度较高的区域,(但不像分子云内部那样致密)比我们仅从硅酸盐和金属氧化物的形成中所能预期的要强,以及(2)化学惰性元素氪显示出弱耗尽的一些证据,这可能是由于被水包合物捕获或与H_3^+结合的结果。

英文摘要:

Ultraviolet spectra of stars recorded by orbiting observatories since the 1970's have revealed absorption features produced by atoms in their favored ionization stages in the neutral ISM of our Galaxy. Most elements show abundances relative to hydrogen that are below their values in stars, indicating their removal by condensation into solid form. The relative amounts of these depletions vary from one location to the next, and different elements show varying degrees of depletion. In a study of abundances along 243 different sight lines reported in more than 100 papers, Jenkins (2009) characterized the systematic patterns for the depletions of 17 different elements, and these results in turn were used to help us understand the compositions of dust grains. Since the conclusions are based on differential depletions along different sightlines, they are insensitive to errors in the adopted values for the total element abundances. Some of the more remarkable conclusions to emerge from this study are that (1) oxygen depletions in the denser gas regions (but not as dense as the interiors of molecular clouds) are stronger than what we can expect from just the formation of silicates and metallic oxides, and (2) the chemically inert element krypton shows some evidence for weak depletion, perhaps as a result of trapping within water clathrates or binding with H_3^+.

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