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Does IRAS 16293–2422 have a hot core? Chemical inventory and abundance changes in its protostellar environment

Schöier, F. L. and Jørgensen, J. K. and van Dishoeck, E. F. and Blake, G. A. (2002) Does IRAS 16293–2422 have a hot core? Chemical inventory and abundance changes in its protostellar environment. Astronomy and Astrophysics, 390 (3). pp. 1001-1021. ISSN 0004-6361. http://resolver.caltech.edu/CaltechAUTHORS:20120919-111530648

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Abstract

A detailed radiative transfer analysis of the observed continuum and molecular line emission toward the deeply embedded young stellar object IRAS 16293-2422 is performed. Accurate molecular abundances and abundance changes with radius are presented. The continuum modelling is used to constrain the temperature and density distributions in the envelope, enabling quantitative estimates of various molecular abundances. The density structure is well described by a single power-law falling off as r^(-1.7), i.e., in the range of values predicted by infall models. A detailed analysis of the molecular line emission strengthens the adopted physical model and lends further support that parts of the circumstellar surroundings of IRAS are in a state of collapse. The molecular excitation analysis reveals that the emission from some molecular species is well reproduced assuming a constant fractional abundance throughout the envelope. The abundances and isotope ratios are generally close to typical values found in cold molecular clouds in these cases, and there is a high degree of deuterium fractionation. There are, however, a number of notable exceptions. Lines covering a wide range of excitation conditions indicate for some molecules, e.g., H_2CO, CH_3OH, SO, SO_2 and OCS, a drastic increase in their abundances in the warm and dense inner region of the circumstellar envelope. The location at which this increase occurs is consistent with the radius at which ices are expected to thermally evaporate off the grains. In all, there is strong evidence for the presence of a "hot core" close to the protostar, whose physical properties are similar to those detected towards most high mass protostars except for a scaling factor. However, the small scale of the hot gas and the infalling nature of the envelope lead to very different chemical time scales between low mass and high mass hot cores, such that only very rapidly produced second-generation complex molecules can be formed in IRAS 16293-2422 . Alternatively, the ices may be liberated due to grain-grain collisions in turbulent shear zones where the outflow interacts with the envelope. Higher angular resolution observations are needed to pinpoint the origin of the abundance enhancements and distinguish these two scenarios. The accurate molecular abundances presented for this low-mass protostar serve as a reference for comparison with other objects, in particular circumstellar disks and comets.


Item Type:Article
Related URLs:
URLURL TypeDescription
http://dx.doi.org/10.1051/0004-6361:20020756DOIArticle
http://www.aanda.org/index.php?option=com_article&access=doi&doi=10.1051/0004-6361:20020756&Itemid=129PublisherArticle
ORCID:
AuthorORCID
van Dishoeck, E. F.0000-0001-7591-1907
Blake, G. A.0000-0003-0787-1610
Additional Information:© 2002 ESO. Received 18 March 2002. Accepted 25 May 2002. The authors are grateful to R. Stark and S. Doty for useful discussions. The referee J. Hatchell is thanked for comments that helped to improve the paper. This research was supported by the Netherlands Organization for Scientific Research (NWO) grant 614.041.004, the Netherlands Research School for Astronomy (NOVA) and a NWO Spinoza grant. This article made use of data obtained through the JCMT archive as Guest User at the Canadian Astronomy Data Center, which is operated by the Dominion Astrophysical Observatory for the National Research Council of Canada's Herzberg Institute of Astrophysics.
Funders:
Funding AgencyGrant Number
Nederlandse Organisatie voor Wetenschappelijk Onderzoek (NWO)614.041.004
Nederlandse Onderzoekschool voor de Astronomie (NOVA)UNSPECIFIED
Subject Keywords:stars: formation; stars: individual: IRAS 16293–2422; ISM: abundances; stars: circumstellar matter; radiative transfer; astrochemistry
Record Number:CaltechAUTHORS:20120919-111530648
Persistent URL:http://resolver.caltech.edu/CaltechAUTHORS:20120919-111530648
Official Citation:Does IRAS 16293–2422 have a hot core? Chemical inventory and abundance changes in its protostellar environment F. L. Schöier, J. K. Jørgensen, E. F. van Dishoeck and G. A. Blake A&A 390 (3) 1001-1021 (2002) DOI: http://dx.doi.org/10.1051/0004-6361:20020756
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:34209
Collection:CaltechAUTHORS
Deposited By: Ruth Sustaita
Deposited On:19 Sep 2012 18:39
Last Modified:23 Aug 2017 22:41

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