静止分子云中含冰二氧化碳的性质
The Nature of Carbon Dioxide Bearing Ices in Quiescent Molecular Clouds
摘要：
在致密的分子云中形成的冰的性质代表了活跃恒星形成区域中星际和行星际前物质演化的一组重要初始条件。在可供研究的各种光谱特征中，固体二氧化碳在15微米附近的弯曲模式已被证明是物理条件（尤其是温度）的特别敏感的探针。我们在Q21-1的光谱中对这种吸收特征进行了新的观测，Q21 - 1是一颗背景场星，位于茧星云（IC 5146）的暗灯丝后面。我们显示的配置文件的功能是一致的两个组件（极性+非极性）模型的冰，根据光谱的实验室类似物的温度范围在10- 20 K。极性成分占视线内CO2的85%。我们第一次比较了15微米的配置文件在三个广泛分离的乌云（金牛座，巨蛇座和IC 5146），并表明，它们是无法区分的观测散射。在三个云中观测到的CO2/H2O比率的系统差异对15微米剖面的影响很小或没有影响。冰中元素氧的丰度似乎是一个统一的因素，在三个云中显示出一致的行为。我们的结论是，冰的形成过程是强大的，统一有效的，尽管组成的变化所产生的差异，在O之间的主要物种（H2O，CO2和CO）的冰分布。
英文摘要：
The properties of the ices that form in dense molecular clouds represent an important set of initial conditions in the evolution of interstellar and preplanetary matter in regions of active star formation. Of the various spectral features available for study, the bending mode of solid CO2 near 15 microns has proven to be a particularly sensitive probe of physical conditions, especially temperature. We present new observations of this absorption feature in the spectrum of Q21-1, a background field star located behind a dark filament in the Cocoon Nebula (IC5146). We show the profile of the feature be consistent with a two-component (polar + nonpolar) model for the ices, based on spectra of laboratory analogs with temperatures in the range 10-20K. The polar component accounts for 85% of the CO2 in the line of sight. We compare for the first time 15 micron profiles in three widely separated dark clouds (Taurus, Serpens and IC5146), and show that they are indistinguishable to within observational scatter. Systematic differences in the observed CO2/H2O ratio in the three clouds have little or no effect on the 15 micron profile. The abundance of elemental oxygen in the ices appears to be a unifying factor, displaying consistent behavior in the three clouds. We conclude that the ice formation process is robust and uniformly efficient, notwithstanding compositional variations arising from differences in how the O is distributed between the primary species (H2O, CO2 and CO) in the ices.
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