History of the solar-type protostar IRAS 16293-2422 as told by the cyanopolyynes
History of the solar-type protostar IRAS 16293-2422 as told by the cyanopolyynes
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DOI：
10.1051/0004-6361/201629506
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发表时间：
2017-01-01
影响因子：
6.5
通讯作者：
Wiesenfeld, L.
中科院分区：
文献类型：
--
作者：
Al-Edhari, A. Jaber;Ceccarelli, C.;Wiesenfeld, L.
上下文。氰聚醚是由碳原子链和一个氢原子组成，两边各有一个CN基团。它们在星际介质（ISM）和彗星中几乎无处不在。在过去，它们被用来限制一些分子云的年龄，因为它们的丰度被预测为时间的强烈函数。最后，氰聚乙烯可能含有大量的碳分子。我们对太阳型原恒星IRAS 16293-2422中的氰多炔分布进行了广泛的研究。目标是(i)对这一来源的氰多炔及其同位素进行普查；（ii）推导出它们的丰度如何在原恒星包膜中变化；（iii）通过将观测结果与化学模型的预测结果进行比较，获得IRAS 16293-2422的历史约束。我们分析了IRAM-30对IRAS 162932422的无偏毫米和亚毫米光谱调查数据，命名为TIMASSS。利用所得的谱线能量分布（SLED）与辐射传输代码GRenoble Analysis of Protostellar Envelope Spectra （GRAPES）的预测结果进行比较，得出了IRAS 16293-2422包络层上的cyanpolyyne丰度。最后，将得到的丰度与化学模型ucl_chem的预测结果进行了比较。我们发现了氰乙炔（HC3N）和氰二乙炔（HC5N）的几个谱线，并报道了在太阳型原恒星中首次发现氘化氰乙炔（DC3N）。我们发现，在IRAS 16293-2422的外部冷包膜中，HC3N丰度大致恒定（类似于1.3 x 10(11)），而在尘埃温度超过80 K的内部区域，即预测火山冰解吸发生时，HC3N丰度增加了约100倍。HC5N在外包膜中的丰度与HC3N相似，而在内包膜中的丰度则低约十倍。与化学模型预测的比较提供了对外包层中氧和碳气体丰度的限制，最重要的是，对来源年龄的限制。在内部区域得到的HC3N丰度，以及增加发生的地方，也对尘埃升温到80k所需的时间提供了强烈的限制，这必须比类似的10(3)- 10(4)年短。最后，氰乙炔氘化在外层包络层约为50%
Context. Cyanopolyynes are chains of carbon atoms with an atom of hydrogen and a CN group on either side. They are detected almost everywhere in the interstellar medium (ISM), as well as in comets. In the past, they have been used to constrain the age of some molecular clouds, since their abundance is predicted to be a strong function of time. Finally, cyanopolyynes can potentially contain a large portion of molecular carbon.Aims. We present an extensive study of the cyanopolyynes distribution in the solar-type protostar IRAS 16293-2422. The goals are (i) to obtain a census of the cyanopolyynes in this source and of their isotopologues; (ii) to derive how their abundance varies across the protostar envelope; and (iii) to obtain constraints on the history of IRAS 16293-2422 by comparing the observations with the predictions of a chemical model.Methods. We analysed the data from the IRAM-30 m unbiased millimeter and submillimeter spectral survey towards IRAS 162932422 named TIMASSS. The derived spectral line energy distribution (SLED) of each detected cyanopolyyne was compared with the predictions from the radiative transfer code GRenoble Analysis of Protostellar Envelope Spectra (GRAPES) to derive the cyanopolyyne abundances across the envelope of IRAS 16293-2422. Finally, the derived abundances were compared with the predictions of the chemical model UCL_CHEM.Results. We detect several lines from cyanoacetylene (HC3N) and cyanodiacetylene (HC5N), and report the first detection of deuterated cyanoacetylene, DC3N, in a solar-type protostar. We found that the HC3N abundance is roughly constant (similar to 1.3 x 10(11)) in the outer cold envelope of IRAS 16293-2422, and it increases by about a factor 100 in the inner region where the dust temperature exceeds 80 K, namely when the volcano ice desorption is predicted to occur. The HC5N has an abundance similar to HC3N in the outer envelope and about a factor of ten lower in the inner region. The comparison with the chemical model predictions provides constraints on the oxygen and carbon gaseous abundance in the outer envelope and, most importantly, on the age of the source. The HC3N abundance derived in the inner region, and where the increase occurs, also provide strong constraints on the time taken for the dust to warm up to 80 K, which has to be shorter than similar to 10(3) - 10(4) yr. Finally, the cyanoacetylene deuteration is about 50% in the outer envelope and