Molecular Gas in 21 and 30 μm Sources: The 2 mm and 1.3 mm Spectra of IRAS 21318+5631 and 22272+5435
Molecular Gas in 21 and 30 μm Sources: The 2 mm and 1.3 mm Spectra of IRAS 21318+5631 and 22272+5435
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DOI：
10.3847/1538-4357/ab9b80
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发表时间：
2020-06
期刊：
影响因子：
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通讯作者：
Yong Zhang
中科院分区：
文献类型：
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作者：
Yong Zhang
星周包层红外光谱中21 μm和30 μm发射特征的载流子一直是一个谜。在本文中，我们给出了对IRAS 21318+5631和22272+5435两个具有21和/或30 μm特征的星周包膜的分子线观测结果。我们研究它们是否具有不寻常的气相化学，并寻找两种尘埃特征载体的可能气相前体。光谱覆盖了130-164 GHz和216.5-273 GHz的几个离散频率范围，从而在每个物体中检测到13种分子种类和同位素。旋转图分析进行，以确定分子丰度，柱密度和激发温度。我们没有发现任何在正常的富含碳的恒星中意想不到的分子种类。然而，它们的分子丰度之间存在着微妙的差异。与IRAS 21318+5631相比，IRAS 22272+5435的SiC2和HC3N谱线较强，而si谱线较弱，说明该21 μm源碳含量更高，粉尘形成效率更高。我们讨论了该结果对21 μm和30 μm特征载流子的潜在影响。
The carriers of the 21 and 30 μm emission features in infrared spectra of circumstellar envelopes are a long-standing enigma. In this paper, we present the results of molecular line observations toward two circumstellar envelopes exhibiting the 21 and/or 30 μm features, IRAS 21318+5631 and 22272+5435. We investigate whether they have unusual gas-phase chemistry and search for a possible gas-phase precursor of the carriers of the two dust features. The spectra cover several discrete frequency ranges of 130–164 GHz and 216.5–273 GHz, resulting in a detection of 13 molecular species and isotopologues in each object. A rotation-diagram analysis is carried out to determine the molecular abundances, column densities, and excitation temperatures. We did not discover any molecular species that would be unexpected in a normal C-rich star. Nevertheless, there exists subtle differences between their molecular abundances. IRAS 22272+5435 shows stronger SiC2 and HC3N lines and weaker SiS lines than IRAS 21318+5631, suggesting that this 21 μm source is more carbon-rich and has experienced more efficient dust formation. We discuss the potential implications of the results for the carriers of the 21 μm and 30 μm features.