气态CO--一种分子云演化的示踪剂
Gaseous CO Abundance---An Evolutionary Tracer for Molecular Clouds
摘要：
普朗克冷团是研究分子云演化的初始条件最有希望的对象之一。本文利用普朗克卫星观测的尘埃释放数据和紫金山天文台13.7 m望远镜观测的$^{12}$ CO/ $^{13}$ CO（1-0）谱线数据，研究了早期冷芯（ECC）样品中674个团簇的CO丰度、CO贫化和CO到H的$_{2}$转换因子。CO丰度的中值和平均值分别为0.89 $\times10^{-4}$和1.28 $\times10^{-4}$。CO消耗因子的平均值和中位数分别为1.7和0.9。整个样本的$X_{CO-to-H_{2}}$的中值为$2.8\times10^{20}$ cm $^{-2}$ K $^{-1}$ km $^{-1}$ s。CO丰度、CO贫化因子和CO-H $_{2}$转换因子与其他物理参数（如尘埃温度、尘埃发射率光谱指数、柱密度、体积密度和发光质量比）有很强的（反）相关性。总之，气态CO丰度可以用作分子云演化的示踪剂。
英文摘要：
Planck cold clumps are among the most promising objects to investigate the initial conditions of the evolution of molecular clouds. In this work, by combing the dust emission data from the survey of Planck satellite with the molecular data of $^{12}$CO/$^{13}$CO (1-0) lines from observations with the Purple Mountain Observatory (PMO) 13.7 m telescope, we investigate the CO abundance, CO depletion and CO-to-H$_{2}$ conversion factor of 674 clumps in the early cold cores (ECC) sample. The median and mean values of the CO abundance are 0.89$\times10^{-4}$ and 1.28$\times10^{-4}$, respectively. The mean and median of CO depletion factor are 1.7 and 0.9, respectively. The median value of $X_{CO-to-H_{2}}$ for the whole sample is $2.8\times10^{20}$ cm$^{-2}$K$^{-1}$km$^{-1}$ s. The CO abundance, CO depletion factor and CO-to-H$_{2}$ conversion factor are strongly (anti-)correlated to other physical parameters (e.g. dust temperature, dust emissivity spectral index, column density, volume density and luminosity-to-mass ratio). To conclude, the gaseous CO abundance can be used as an evolutionary tracer for molecular clouds.
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