Blake, Geoffrey A. and Sandell, Göran and van Dishoeck, Ewine F. and Groesbeck, T. D. and Mundy, Lee G. and Aspin, Colin (1995) A molecular line study of NGC 1333/IRAS 4. Astrophysical Journal, 441 (2). pp. 689-701. ISSN 0004-637X. http://resolver.caltech.edu/CaltechAUTHORS:20120912-131307372
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Molecular line surveys and fully sampled spectral line maps at 1.3 and 0.87 mm are used to examine the physical and chemical characteristics of the extreme Class I sources IRAS 4A and 4B in the L1450/NGC 1333 molecular cloud complex. A very well collimated, jetlike molecular outflow emanates from IRAS 4A, with a dynamical age of a few thousand years. Symmetric, clumpy structure along the outflow lobes suggests that there is considerable variability in the mass-loss rate or wind velocity even at this young age. Molecular emission lines toward IRAS 4A and 4B are observed to be weak in the velocity range corresponding to quiescent material surrounding the young stellar objects (YSOs). Depletion factors of 10-20 are observed for αll molecules, including CO, even for very conservative mass estimates from the measured millimeter and submillimeter dust continuum. However, abundances scaled with respect to CO are similar to other dark molecular cloud cores. Such depletions could be mimicked by high dust optical depths or increased grain emissivities at the observing frequencies of 230 and 345 GHz, but the millimeter and submillimeter spectral energy distributions suggest that this is unlikely over the single-dish size scales of 5000-10,000 AU. Dense, outflowing gas is found to be kinematically, but not spatially, distinct from the quiescent material on these size scales. If CO is used as a chemical standard for the high-velocity gas, we find substantial enhancements in the abundances of several molecules in outflowing material, most notably CS, SiO, and CH_30H. The SiO emission is kinematically well displaced from the bulk cloud velocity and likely arises from directly shocked material. As is the case for CO, however, the outflow features from more volatile species are centered near the cloud velocity and are often characterized by quite low rotational temperatures. We suggest that grain-grain collisions induced by velocity shear zones surrounding the outflow axes transiently desorb the grain mantles, resulting in large abundance enhancements of selected species. Similar results have recently been obtained in several other low-mass YSOs, where the outflowing gas is often both kinematically and spatially distinct, and are illustrative of the ability of accretion and outflow processes to simultaneously modify the composition of the gas and dust surrounding young stars.
|Additional Information:||© 1995 American Astronomical Society. Provided by the NASA Astrophysics Data System. Received 1994 June 16; accepted 1994 September 22. G. A. B. would like to acknowledge support from NASA (NAGW-2297) as well as the David and Lucille Packard and Alfred P. Sloan Foundations, which work on astrochemistry in Leiden is supported by a PIONIER grant from the Netherlands Organization for Scientific Research (NWO). L. G. M. acknowledges support from NASA (NAGW-3066). The authors would also like to thank M. Greenberg and S. Sandford for helpful discussions on grain mantle processing.|
|Subject Keywords:||ISM: abundances; ISM: individual (NGC 1333); ISM: jets and outflows; ISM: molecules; stars: formation|
|Official Citation:||A molecular line study of NGC 1333/IRAS 4 Blake, Geoffrey A.; Sandell, Goran; van Dishoeck, Ewine F.; Groesbeck, T. D.; Mundy, Lee G.; Aspin, Colin|
|Usage Policy:||No commercial reproduction, distribution, display or performance rights in this work are provided.|
|Deposited By:||Ruth Sustaita|
|Deposited On:||12 Sep 2012 20:38|
|Last Modified:||26 Dec 2012 16:09|
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