The abundant elements in interstellar dust
The abundant elements in interstellar dust
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星际尘埃中丰富的元素
DOI：
10.1086/174438
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发表时间：
1994
期刊：
影响因子：
--
通讯作者：
B. Savage
中科院分区：
文献类型：
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作者：
U. Sofia;J. Cardelli;B. Savage
我们探索了宇宙中丰富的O、C、N、Mg、Si、Fe和S物种进入星际尘埃的过程。使用戈达德高分辨率光谱仪3.5公里/S分辨率测量的柱密度，对五条视线的八个单独吸收区域进行了分辨率测量。根据需要进行修正，以说明振荡器强度最近的改进。为了获得最准确的柱密度，并检查振子强度的准确性，我们将基于很强的洛伦兹阻尼线的柱密度与这些物种的弱线的结果进行了比较，并确认了先前确定的O I波长1335、C II波长2325和N1波长1159、1160的f值。新的经验f值分别为1.25×10(exp-3)和6.25×10(exp-4)，分别为1239和1240A处的Mg II弱双星。假定基于太阳和B星值的宇宙参考丰度，我们得到了亏损和尘相丰度，这表明超过70%的有效镁和铁被并入尘埃颗粒核，而只有35%的硅被并入尘粒核。这意味着氧化物是谷物核心种群的重要组成部分。镁和铁原子以1.8：1的比例被包裹在晶核上，而每个铁原子大约有4.0个硅原子在地幔中。由于预计硅不会附着在硅酸盐或石墨颗粒上，其他颗粒核心，可能是氧化物和/或金属铁，可能为这种物种提供地幔位置。地幔中铁和镁的丰度表明，除非氧化物为这些物种提供了重要的地幔位置，否则石墨颗粒一定有很大的覆盖层。太阳参考丰度值所暗示的尘埃相中O和N的丰度很难与这些元素预计不参与地幔形成的事实相一致，而且3.1微米的H2O冰特征在吸收类似于所研究的恒星时也看不到。然而，O和N的B星参考丰度意味着这些物种没有发生地幔作用。太阳参考丰度所暗示的碳的尘埃相丰度与产生2175A撞击所需的石墨颗粒数量的预测一致。然而，B星的参考丰度表明，尘埃相中的C丰度并不总是足以产生凸起。
We explore the incorporation of the cosmically abundant species O, C, N, Mg, Si, Fe, and S into interstellar dust. Column densities based on Goddard High Resolution Spectrograph 3.5 km/s resolution measurements from the literature for eight individual absorbing regions toward five lines of sight are used. Corrections are applied as needed in order to account for recent improvements in oscillator strengths. In order to acquire the most accurate column densities, and check on the accuracy of the oscillator strengths, we compare column densities based on the very strong Lorentzian damped lines of C II, O I, N I, and Mg II with results for the weak lines of these species, and confirm the previously determined f-values for O I lambda 1335, C II lambda 2325, and N I lambda lambda 1159, 1160. New empirical f-values of 1.25 x 10(exp -3) and 6.25 x 10(exp -4), respectively, are derived for the Mg II weak doublet at 1239 and 1240 A. Assuming a cosmic reference abundance based on solar and B star values, we derive depletions and dust-phase abundances which suggest that more than 70% of the available Mg and Fe is incorporated into dust-grain cores, whereas only 35% of the silicon is. This implies that oxides are important constituents of the grain core population. Mg and Fe atoms are mantled onto grain cores in a ratio of 1.8 to 1, whereas approximately 4.0 Si atoms are in the mantle per Fe atom. Since Si is not expected to accrete onto silicate or graphite grains, other grain cores, perhaps oxides and/or metallic Fe, may provide mantling sites for this species. The abundances of Fe and Mg in mantles would imply that graphite grains must have a substantial coating unless oxides provide significant mantling sites for these species. The abundance of O and N in the dust phase as implied by the solar reference abundance values are difficult to reconcile with the fact that these elements are not expected to participate in mantle formation, and the 3.1 micrometer H2O ice feature is not seen in absorption toward stars similar to those studied. The B star reference abundances for O and N, however, imply that no mantling of these species has occurred. The dust-phase abundance for C implied by solar reference abundances agrees with predictions for the number of graphite grains needed to produce the 2175 A bump. B star reference abundances, however, suggest that the abundance of C in the dust phase is not always sufficient to produce the bump.