Interstellar solid CO: polar and nonpolar interstellar ices.
Interstellar solid CO: polar and nonpolar interstellar ices.
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星际固体CO：极性和非极性星际冰。
DOI：
10.1086/170640
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发表时间：
1991
期刊：
影响因子：
--
通讯作者：
F. Baas
中科院分区：
文献类型：
--
作者：
A. Tielens;A. Tokunaga;T. Geballe;F. Baas
我们对原恒星样本中的固体 CO 带进行了中等分辨率（lambda/delta lambda 约为 1200）的观测。光谱显示沿大多数视线有两个独立的固体二氧化碳成分。一种产生窄带（δ nu 约 5 cm-1），一般集中在约 2140 cm-1 处，另一种则产生较宽的带（δ nu 约 10 cm-1），中心在约 2136 cm-1 处。狭窄且通常最强的成分的峰值位置和宽度因物体而异。该样本中两种成分的相对强度差异很大。对天体物理相关混合物中固体CO带的形状和峰值位置的实验室研究表明，窄CO带出现在以非极性分子（例如CO本身、CO2、O2、N2）为主的混合物中，而宽特征是由于极性更强的混合物，例如H2O冰。计算表明，对于以 CO 为主的混合物（CO 浓度 > 0.3），CO 基波的峰位置和形状受到“表面模式”的强烈影响，而对于较低浓度，实验室测量的吸收光谱提供了非常准确的小颗粒消光光谱表示。观测到的星际 2140 cm-1 成分的峰值位置和宽度的变化可归因于颗粒的成分和/或物理特性（即形状）的变化。这些观测结果表明，许多视线包含（至少）两种独立的颗粒地幔成分：一种负责 3.08 和 6.0 微米冰带的极性混合物（富含 H2O）和一种主导固体 CO 光谱的非极性混合物。这两个独立的颗粒地幔成分可能反映了吸积过程中的化学变化。在发光原恒星周围，非极冰和富含水的冰的波动性差异也可能在决定其相对丰度方面发挥重要作用。
We present moderate-resolution (lambda/delta lambda approximately 1200) observations of the solid CO band in a sample of protostars. The spectra reveal two independent solid CO components along most lines of sight. One produces a narrow (delta nu approximately 5 cm-1) band generally centered at about 2140 cm-1 and the other a broader (delta nu approximately 10 cm-1) one at about 2136 cm-1. Both the peak position and width of the narrow, and generally strongest, component vary from object to object. The relative strengths of the two components vary considerably in this sample. Laboratory studies of the shape and peak position of the solid CO banD in astrophysically relevant mixtures show that the narrow CO band occurs in mixtures dominated by non-polar molecules (e.g., CO itself, CO2, O2, N2), while the broad feature is due to more polar mixtures, such as H2O ice. Calculations show that for mixtures dominated by CO (CO concentration > 0.3), the peak position and shape of the CO fundamental are strongly influenced by "surface modes," while for lower concentrations the laboratory measured absorption spectra provide very accurate representations of the small particle extinction spectrum. The observed variations in peak position and width of the interstellar 2140 cm-1 component can be attributed to variations in composition and/or physical characteristics of the grains (i.e., shape). These observations show that many lines of sight contain (at least) two independent grain mantle components: a polar mixture (H2O-rich) responsible for the 3.08 and 6.0 micrometers ice bands and a nonpolar one dominating the solid CO spectrum. These two independent grain mantle components may reflect chemical variations during accretion. Around luminous protostars, differences in volatility of the nonpolar and H2O-rich ices also may play an important role in determining their relative abundances.