Volume 518, July-August 2010
Herschel: the first science highlights
|Number of page(s)||5|
|Published online||16 July 2010|
Letter to the Editor
Water cooling of shocks in protostellar outflows*
Herschel-PACS map of L1157
INAF - Osservatorio Astronomico di Roma, Via di Frascati 33, 00040 Monte Porzio Catone, Italy e-mail: firstname.lastname@example.org
2 INAF - Istituto di Fisica dello Spazio Interplanetario, Area di Ricerca di Tor Vergata, via Fosso del Cavaliere 100, 00133 Roma, Italy
3 INAF - Osservatorio Astrofisico di Arcetri, Largo E. Fermi 5, 50125 Firenze, Italy
4 Department of Radio and Space Science, Chalmers University of Technology, Onsala Space Observatory, 439 92 Onsala, Sweden
5 Department of Physics and Astronomy, Johns Hopkins University, 3400 North Charles Street, Baltimore, MD 21218, USA
6 IGN Observatorio Astronómico Nacional, Apartado 1143, 28800 Alcalá de Henares, Spain
7 Leiden Observatory, Leiden University, PO Box 9513, 2300 RA Leiden, The Netherlands
8 Max Planck Institut for Extraterestrische Physik, Garching, Germany
9 Université de Bordeaux, Laboratoire d'Astrophysique de Bordeaux, France; CNRS/INSU, UMR 5804, Floirac, France
10 Institute of Astronomy, ETH Zurich, 8093 Zurich, Switzerland
11 Department of Astronomy, The University of Michigan, 500 Church Street, Ann Arbor, MI 48109-1042, USA
12 California Institute of Technology, Division of Geological and Planetary Sciences, MS 150-21, Pasadena, CA 91125, USA
13 School of Physics and Astronomy, University of Leeds, Leeds LS2 9JT, UK
14 Centro de Astrobiología. Departamento de Astrofísica. CSIC-INTA. Carretera de Ajalvir, Km 4, Torrejón de Ardoz. 28850, Madrid, Spain
15 LERMA and UMR 8112 du CNRS, Observatoire de Paris, 61 Av. de l'Observatoire, 75014 Paris, France
16 Astronomical Institute Anton Pannekoek, University of Amsterdam, Kruislaan 403, 1098 SJ Amsterdam, The Netherlands
17 Department of Astrophysics/IMAPP, Radboud University Nijmegen, PO Box 9010, 6500 GL Nijmegen, The Netherlands
18 Department of Physics and Astronomy, Denison University, Granville, OH, 43023, USA
19 University of Waterloo, Department of Physics and Astronomy, Waterloo, Ontario, Canada
20 SRON Netherlands Institute for Space Research, PO Box 800, 9700 AV, Groningen, The Netherlands
21 National Research Council Canada, Herzberg Institute of Astrophysics, 5071 West Saanich Road, Victoria, BC V9E 2E7, Canada
22 Department of Physics and Astronomy, University of Victoria, Victoria, BC V8P 1A1, Canada
23 Centre for Star and Planet Formation, Natural History Museum of Denmark, University of Copenhagen, Øster Voldgade 5-7, 1350 Copenhagen, Denmark
24 Department of Physics and Astronomy, San Jose State University, One Washington Square, San Jose, CA 95192, USA
25 Department of Astronomy, Stockholm University, AlbaNova, 106 91 Stockholm, Sweden
26 Harvard-Smithsonian Center for Astrophysics, 60 Garden Street, MS 42, Cambridge, MA 02138, USA
27 Jet Propulsion Laboratory, California Institute of Technology, Pasadena, CA 91109, USA
28 Department of Physics and Astronomy, University of Calgary, Calgary, T2N 1N4, AB, Canada
29 Department of Physics and Astronomy, University College London, Gower Street, London WC1E6BT, UK
30 Max-Planck-Institut für Radioastronomie, Auf dem Hügel 69, 53121 Bonn, Germany
31 Kapteyn Astronomical Institute, University of Groningen, PO Box 800, 9700 AV, Groningen, The Netherlands
32 Institute Laboratoire d'Etudes du Rayonnement et de la Matire en Astrophysique, UMR 8112 CNRS/INSU, OP, ENS, UPMC, UCP, Paris, France
33 CNRS/INSU, UMR 5804, B.P. 89, 33271 Floirac cedex, France
34 Institute Institut de Radioastronomie Millimetrique, IRAM, 300 rue de la Piscine, 38406 St Martin d'Heres, France
35 KOSMA, I. Physik. Institut, Universität zu Köln, Zülpicher Str. 77, 50937 Köln, Germany
36 European Space Astronomy Centre, ESA, PO Box 78, 28691 Villanueva de la Caada, Madrid, Spain
Accepted: 23 April 2010
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 H2O 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-H2O 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 H2O abundance and total cooling.
Results. Strong H2O peaks are localized on both shocked emission knots and the central source position. The H2O 179 μm emission is spatially correlated with emission from H2 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 NH3. A strong H2O 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 H2O 557 GHz line previously observed with Odin/SWAS indicate that the water emission originates in warm compact clumps, spatially unresolved by PACS, having a H2O 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 H2O cooling is ~10-1 , about 40% of the cooling due to H2 and 23% of the total energy released in shocks along the L1157 outflow.
Key words: stars: formation / ISM: jets and outflows / ISM: molecules
© ESO, 2010
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