Radiation transport and non-LTE analysis of interstellar molecular lines. I. Carbon Monoxide
Radiation transport and non-LTE analysis of interstellar molecular lines. I. Carbon Monoxide
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星际分子线的辐射传输和非 LTE 分析。
DOI：
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发表时间：
1976
期刊：
影响因子：
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通讯作者：
H. Liszt
中科院分区：
文献类型：
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作者：
C. Leung;H. Liszt
本文给出了一氧化碳10个最低转动跃迁的辐射传输和统计平衡耦合方程的数值解。理论模型构建的巨分子云与H II地区和简单的黑暗尘埃云，使用静态，球形模型和微观湍流速度场。结果提出了一系列的CO丰度和光学深度。现有的观测证据进行了总结和详细的比较，在强度，形状和宽度的计算线剖面。我们的计算成功地再现了大量的/sup 12/CO和/sup 13/CO在j=1- 0和j=2- 1跃迁中的观测结果，只要/sup 12/CO相对于分子氢的相对丰度（/sup 12/CO）/（H/sub 2/）约为. =（1--4）x 10/sup -5/。因此，在j=1- 0线中的/sup 12/CO光学深度比先前假定的小10倍，给出τ approx。=（1- 4）.一个非LTE分析的激励机制，并在小的光学深度的线联锁的重要性进行了讨论。在非LTE条件下的/sup 13/CO线的增强和/sup 12/CO线中的大饱和效应（甚至在τ近似大于1时）有助于将j=1- 0跃迁中的/sup 13/CO//sup 12/CO的强度比降低到观察值4，即使同位素比为约40。这些结果的其他影响进行了讨论。(AIP)«少
We present numerical solutions to the coupled equations of radiative transfer and statistical equilibrium in the 10 lowest rotational transitions of carbon monoxide. Theoretical models are constructed for giant molecular clouds associated with H II regions and for simple dark dust clouds, using static, spherical models and a microturbulent velocity field. Results are presented for a range of CO abundances and optical depths. Available observational evidence is summarized and detailed comparisons are made in terms of intensity, shape, and width of the computed line profiles. Our calculations reproduce successfully a large body of observations of /sup 12/CO and /sup 13/CO in the j=1--0 and j=2--1 transitions, as long as the relative abundance of /sup 12/CO to molecular hydrogen (/sup 12/CO)/(H/sub 2/)approx. = (1--4) x 10/sup -5/. Consequently, the /sup 12/CO optical depths in the j=1--0 line are smaller than previously assumed, by a factor of 10, giving tauapprox. = (1--4). A non-LTE analysis of the excitation mechanism is made and the importance of line interlocking at small optical depths is discussed. Enhancement of the /sup 13/CO line under non-LTE conditions and large saturation effects in the /sup 12/CO line (even at tauapproximately-greater-than1) help to reduce the intensity ratio of /supmore » 12/CO//sup 13/CO in the j=1--0 transition to the observed value of 4, even with an isotopic ratio of approx.40. Other implications of these results are discussed. (AIP)« less