Tracing the cold and warm physico-chemical structure of deeply embedded protostars: IRAS 16293−2422 vs. VLA 1623−2417
Leiden Observatory, Leiden University,
PO Box 9513,
Leiden, The Netherlands
2 Max-Planck-Institut für extraterrestrische Physik, Giessenbachstraße 1, 85748 Garching bei München, Germany
3 Centre for Star and Planet Formation, Niels Bohr Institute & Natural History Museum of Denmark, University of Copenhagen, Øster Voldgade 5–7, 1350 Copenhagen K., Denmark
4 ASTRON, the Netherlands Institute for Radio Astronomy, Postbus 2, 7990 AA Dwingeloo, The Netherlands
5 Center for Space and Habitability (CSH), University of Bern, Sidlerstrasse 5, 3012 Bern, Switzerland
Accepted: 29 April 2018
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.
Key words: astrochemistry / stars: formation / stars: low-mass / stars: individual: IRAS 16293–2422 / methods: observational / stars: individual: VLA 1623–2417
© ESO 2018