Tracing the cold and warm physico-chemical structure of deeply embedded protostars: IRAS 16293-2422 vs. VLA 1623-2417
Abstract
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-C3H2 and 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-C3H2 and C2H. For IRAS 16293-2422, c-C3H2 traces 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.
- Publication:
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Astronomy and Astrophysics
- Pub Date:
- September 2018
- DOI:
- 10.1051/0004-6361/201731724
- arXiv:
- arXiv:1805.05205
- Bibcode:
- 2018A&A...617A.120M
- Keywords:
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- astrochemistry;
- stars: formation;
- stars: low-mass;
- stars: individual: IRAS 16293-2422;
- methods: observational;
- stars: individual: VLA 1623-2417;
- Astrophysics - Solar and Stellar Astrophysics;
- Astrophysics - Astrophysics of Galaxies
- E-Print:
- 24 pages, 15 figures, accepted to A&