Jørgensen, J. K. and Hogerheijde, M. R. and Blake, G. A. and van Dishoeck, E. F. and Mundy, L. G. and Schöier, F. L. (2004) The impact of shocks on the chemistry of molecular clouds - High resolution images of chemical differentiation along the NGC 1333–IRAS 2A outflow. Astronomy and Astrophysics, 415 (3). pp. 1021-1037. ISSN 0004-6361 http://resolver.caltech.edu/CaltechAUTHORS:20120918-115240547
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This paper presents a detailed study of the chemistry in the outflow associated with the low-mass protostar NGC 1333-IRAS 2A down to 3" (650 AU) scales. Millimeter-wavelength aperture-synthesis observations from the Owens Valley and Berkeley-Illinois-Maryland-Association interferometers and (sub)millimeter single-dish observations from the Onsala Space Observatory 20 m telescope and Caltech Submillimeter Observatory are presented. The interaction of the highly collimated protostellar outflow with a molecular condensation ~15000 AU from the central protostar is clearly traced by molecular species such as HCN, SiO, SO, CS, and CH_(3)OH. Especially SiO traces a narrow high velocity component at the interface between the outflow and the molecular condensation. Multi-transition single-dish observations are used to distinguish the chemistry of the shock from that of the molecular condensation and to address the physical conditions therein. Statistical equilibrium calculations reveal temperatures of 20 and 70 K for the quiescent and shocked components, respectively, and densities near 10^6 cm^(-3). The line-profiles of low- and high-excitation lines are remarkably similar, indicating that the physical properties are quite homogeneous within each component. Significant abundance enhancements of two to four orders of magnitude are found in the shocked region for molecules such as CH_(3)OH, SiO and the sulfur-bearing molecules. HCO^+ is seen only in the aftermath of the shock consistent with models where it is destroyed through release of H_(2)O from grain mantles in the shock. N_(2)H^+ shows narrow lines, not affected by the outflow but rather probing the ambient cloud. The overall molecular inventory is compared to other outflow regions and protostellar environments. Differences in abundances of HCN, H_(2)CO and CS are seen between different outflow regions and are suggested to be related to differences in the atomic carbon abundance. Compared to the warm inner parts of protostellar envelopes, higher abundances of in particular CH_(3)OH and SiO are found in the outflows, which may be related to density differences between the regions.
|Additional Information:||© 2004 ESO. Article published by EDP Sciences. Received 21 August 2003; accepted 3 November 2003. We thank the referee for a prompt and well-considered report. The research of JKJ is funded by the Netherlands Research School for Astronomy (NOVA) through a network 2 Ph.D. stipend and research in astrochemistry in Leiden is supported by a Spinoza grant. GAB acknowledges support from the NASA Origins of Solar Systems program. FLS further acknowledges financial support from the Swedish Research Council.|
|Subject Keywords:||ISM: individual objects: NGC 1333–IRAS 2; stars: formation; ISM: jets and outflows; ISM: abundances|
|Official Citation:||The impact of shocks on the chemistry of molecular clouds - High resolution images of chemical differentiation along the NGC 1333–IRAS 2A outflow J. K. Jørgensen, M. R. Hogerheijde, G. A. Blake, E. F. van Dishoeck, L. G. Mundy and F. L. Schöier A&A 415 (3) 1021-1037 (2004) DOI: http://dx.doi.org/10.1051/0004-6361:20034216|
|Usage Policy:||No commercial reproduction, distribution, display or performance rights in this work are provided.|
|Deposited By:||Jason Perez|
|Deposited On:||18 Sep 2012 22:19|
|Last Modified:||26 Dec 2012 16:12|
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