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标题：Tracing the cold and warm physico-chemical structure of deeply embedded protostars: IRAS 16293−2422 vs. VLA 1623−2417
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作者：N. M. Murillo ; E. F. van Dishoeck ; M. H. D. van der Wiel 等
期刊名称：Astronomy & Astrophysics
印刷版ISSN：0004-6361
电子版ISSN：1432-0746
出版年度：2018
卷号：617
DOI：10.1051/0004-6361/201731724
语种：English
出版社：EDP Sciences
摘要：Context.Much attention has been placed on the dust distribution in protostellar envelopes, but there are still many unanswered questions regarding the physico-chemical structure of the gas.Aims.Our aim is to start identifying the factors that determine the chemical structure of protostellar regions, by studying and comparing low-mass embedded systems in key molecular tracers.Methods.The cold and warm chemical structures of two embedded Class 0 systems, IRAS 16293−2422 and VLA 1623−2417 were characterized through interferometric observations. DCO+, N2H+, and N2D+were used to trace the spatial distribution and physics of the cold regions of the envelope, while c-C3H2and C2H from models of the chemistry are expected to trace the warm (UV-irradiated) regions.Results.The two sources show a number of striking similarities and differences. DCO+consistently traces the cold material at the disk-envelope interface, where gas and dust temperatures are lowered due to disk shadowing. N2H+and N2D+, also tracing cold gas, show low abundances toward VLA 1623−2417, but for IRAS 16293−2422, the distribution of N2D+is consistent with the same chemical models that reproduce DCO+. The two systems show different spatial distributions c-C3H2and C2H. For IRAS 16293−2422, c-C3H2traces the outflow cavity wall, while C2H is found in the envelope material but not the outflow cavity wall. In contrast, toward VLA 1623−2417 both molecules trace the outflow cavity wall. Finally, hot core molecules are abundantly observed toward IRAS 16293−2422 but not toward VLA 1623−2417.Conclusions.We identify temperature as one of the key factors in determining the chemical structure of protostars as seen in gaseous molecules. More luminous protostars, such as IRAS 16293−2422, will have chemical complexity out to larger distances than colder protostars, such as VLA 1623−2417. Additionally, disks in the embedded phase have a crucial role in controlling both the gas and dust temperature of the envelope, and consequently the chemical structure.
关键词：Key wordsenastrochemistrystars: formationstars: low-massstars: individual: IRAS 16293–2422methods: observationalstars: individual: VLA 1623–2417