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Water cooling of shocks in protostellar outflows: Herschel-PACS map of L1157

Nisini, B. and Blake, G. A. and Lis, D. (2010) Water cooling of shocks in protostellar outflows: Herschel-PACS map of L1157. Astronomy and Astrophysics, 518 . L120. ISSN 0004-6361.

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Context. The far-IR/sub-mm spectral mapping facility provided by the Herschel-PACS and HIFI instruments has made it possible to obtain, for the first time, images of H_2O emission with a spatial resolution comparable to ground based mm/sub-mm observations. Aims. In the framework of the Water In Star-forming regions with Herschel (WISH) key program, maps in water lines of several outflows from young stars are being obtained, to study the water production in shocks and its role in the outflow cooling. This paper reports the first results of this program, presenting a PACS map of the o-H_2O 179 μm transition obtained toward the young outflow L1157. Methods. The 179 μm map is compared with those of other important shock tracers, and with previous single-pointing ISO, SWAS, and Odin water observations of the same source that allow us to constrain the H_2O abundance and total cooling. Results. Strong H_2O peaks are localized on both shocked emission knots and the central source position. The H_2O 179 μm emission is spatially correlated with emission from H_2 rotational lines, excited in shocks leading to a significant enhancement of the water abundance. Water emission peaks along the outflow also correlate with peaks of other shock-produced molecular species, such as SiO and NH_3. A strong H_2O peak is also observed at the location of the proto-star, where none of the other molecules have significant emission. The absolute 179 μm intensity and its intensity ratio to the H_2O 557 GHz line previously observed with Odin/SWAS indicate that the water emission originates in warm compact clumps, spatially unresolved by PACS, having a H_2O  abundance of the order of 10^(-4). This testifies that the clumps have been heated for a time long enough to allow the conversion of almost all the available gas-phase oxygen into water. The total H_2O cooling is ~10^(-1) L_☉, about 40% of the cooling due to H_2 and 23% of the total energy released in shocks along the L1157 outflow.

Item Type:Article
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Blake, G. A.0000-0003-0787-1610
Lis, D.0000-0002-0500-4700
Additional Information:© 2010 ESO. Received 31 March 2010; Accepted 23 April 2010; Published online 16 July 2010. Herschel is an ESA space observatory with science instruments provided by European-led Principal Investigator consortia and with important partecipation from NASA. This program is made possible thanks to the HIFI guaranteed time and the PACS instrument builders.
Subject Keywords:stars: formation; ISM: jets and outflows; ISM: molecules
Record Number:CaltechAUTHORS:20101123-111630361
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Official Citation:Water cooling of shocks in protostellar outflows - Herschel-PACS map of L1157 B. Nisini, M. Benedettini, C. Codella, T. Giannini, R. Liseau, D. Neufeld, M. Tafalla, E. F. van Dishoeck, R. Bachiller, A. Baudry, A. O. Benz, E. Bergin, P. Bjerkeli, G. Blake, S. Bontemps, J. Braine, S. Bruderer, P. Caselli, J. Cernicharo, F. Daniel, P. Encrenaz, A. M. di Giorgio, C. Dominik, S. Doty, M. Fich, A. Fuente, J. R. Goicoechea, Th. de Graauw, F. Helmich, G. Herczeg, F. Herpin, M. Hogerheijde, T. Jacq, D. Johnstone, J. Jørgensen, M. Kaufman, L. Kristensen, B. Larsson, D. Lis, M. Marseille, C. McCoey, G. Melnick, M. Olberg, B. Parise, J. Pearson, R. Plume, C. Risacher, J. Santiago, P. Saraceno, R. Shipman, T. A. van Kempen, R. Visser, S. Viti, S. Wampfler, F. Wyrowski, F. van der Tak, U. A. Yıldız, B. Delforge, J. Desbat, W. A. Hatch, I. Péron, R. Schieder, J. A. Stern, D. Teyssier and N. Whyborn A&A 518 L120 (2010) DOI: 10.1051/0004-6361/201014603
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:20983
Deposited By: Jason Perez
Deposited On:30 Nov 2010 23:43
Last Modified:03 Oct 2019 02:18

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