A 3 mm molecular line survey toward the C-star envelope CIT 6
A 3 mm molecular line survey toward the C-star envelope CIT 6
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DOI：
10.1093/pasj/psad043
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发表时间：
2023-07
影响因子：
2.3
通讯作者：
Kuilu Yang;Yong Zhang;J. Qiu;Yina Ao;Xiaohu Li
中科院分区：
文献类型：
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作者：
Kuilu Yang;Yong Zhang;J. Qiu;Yina Ao;Xiaohu Li
我们提出了一个公正的分子线调查对富碳拱星信封CIT 6进行90和116 GHz之间的亚利桑那州射电天文台12米望远镜。共检测到42条谱线，分别归属于10种分子和4种同位素。尽管没有任何新发现的拱星分子，几个转变是新鲜报道的这个对象。这项工作是对我们以前在36-49 GHz和131-268 GHz频率范围内对CIT 6进行的线路调查的补充。基于测量和结合以前发表的数据，我们进行旋转图分析，以确定柱密度，激发温度，和分数丰度的分子。激发温度沿半径沿着变化。CIT 6的丰度模式与原型C星IRC +10216在指定的检测灵敏度下的丰度模式大致一致，表明IRC +10216中的分子丰度不能归因于对不寻常化学的解释。然而，这两颗C星之间的细微差别被发现，与IRC +10216相比，CIT 6中碳链分子的丰度更高，12 C $/13 C $的比值更低，这意味着前者比后者质量更大或处于更演化的阶段。
We present an unbiased molecular line survey toward the carbon-rich circumstellar envelope CIT 6 carried out between 90 and 116 GHz with the Arizona Radio Observatory 12 m telescope. A total of 42 lines assigned to 10 molecular species and four isotopologues are detected. Despite the absence of any newly identified circumstellar molecules, several transitions are freshly reported for this object. This work is a complement to our previous line survey toward CIT 6 in the frequency ranges of 36–49 GHz and 131–268 GHz. Based on the measurements and in combination with previously published data, we perform a rotation-diagram analysis to determine the column densities, excitation temperatures, and fractional abundances of the molecules. The excitation temperature varies along the radius. The abundance pattern of CIT 6 is broadly consistent with that of the prototype C-star IRC +10216 at the specified detection sensitivity, indicating that the molecular richness in IRC +10216 cannot be attributed to an interpretation of unusual chemistry. Nevertheless, subtle distinctions between the two C-stars are found. The higher abundance of carbon-chain molecules and lower 12C$/$13C ratio in CIT 6 compared to IRC +10216 imply that the former is more massive or in a more evolved phase than the latter.