Letter to the Editor

Water in low-mass star-forming regions with Herschel ^*,**

HIFI spectroscopy of NGC 1333

¹ Leiden Observatory, Leiden University, PO Box 9513, 2300 RA Leiden, The Netherlands
² Max Planck Institut für Extraterrestrische Physik, Giessenbachstrasse 1, 85748 Garching, Germany
³ Department of Physics and Astronomy, Denison University, Granville, OH, 43023, USA
⁴ Max-Planck-Institut für Radioastronomie, Auf dem Hügel 69, 53121 Bonn, Germany
⁵ Centre for Star and Planet Formation, Natural History Museum of Denmark, University of Copenhagen, Øster Voldgade 5–7, 1350 Copenhagen K., Denmark
⁶ Harvard-Smithsonian Center for Astrophysics, 60 Garden Street, MS 42, Cambridge, MA 02138, USA
⁷ Institute of Astronomy, ETH Zurich, 8093 Zurich, Switzerland
⁸ Observatorio Astronómico Nacional (IGN), Calle Alfonso XII 3, 28014 Madrid, Spain
⁹ Université de Bordeaux, Laboratoire d'Astrophysique de Bordeaux, France; CNRS/INSU, UMR 5804, Floirac, France
¹⁰ INAF – Instituto di Fisica dello Spazio Interplanetario, Area di Ricerca di Tor Vergata, via Fosso del Cavaliere 100, 00133 Roma, Italy
¹¹ Department of Astronomy, University of Michigan, 500 Church Street, Ann Arbor, MI 48109-1042, USA
¹² Department of Radio and Space Science, Chalmers University of Technology, Onsala Space Observatory, 439 92 Onsala, Sweden
¹³ California Institute of Technology, Division of Geological and Planetary Sciences, MS 150-21, Pasadena, CA 91125, USA
¹⁴ School of Physics and Astronomy, University of Leeds, Leeds LS2 9JT, UK
¹⁵ INAF – Osservatorio Astrofisico di Arcetri, Largo E. Fermi 5, 50125 Firenze, Italy
¹⁶ Centro de Astrobiología, Departamento de Astrofísica, CSIC-INTA, Carretera de Ajalvir, Km 4, Torrejón de Ardoz, 28850 Madrid, Spain
¹⁷ SRON Netherlands Institute for Space Research, PO Box 800, 9700 AV Groningen, The Netherlands
¹⁸ Astronomical Institute Anton Pannekoek, University of Amsterdam, Kruislaan 403, 1098 SJ Amsterdam, The Netherlands
¹⁹ Department of Astrophysics/IMAPP, Radboud University Nijmegen, PO Box 9010, 6500 GL Nijmegen, The Netherlands
²⁰ LERMA and UMR 8112 du CNRS, Observatoire de Paris, 61 Av. de l'Observatoire, 75014 Paris, France
²¹ University of Waterloo, Department of Physics and Astronomy, Waterloo, Ontario, Canada
²² Observatorio Astronómico Nacional, Apartado 112, 28803 Alcalá de Henares, Spain
²³ INAF – Osservatorio Astronomico di Roma, 00040 Monte Porzio catone, Italy
²⁴ National Research Council Canada, Herzberg Institute of Astrophysics, 5071 West Saanich Road, Victoria, BC V9E 2E7, Canada
²⁵ Department of Physics and Astronomy, University of Victoria, Victoria, BC V8P 1A1, Canada
²⁶ Department of Physics and Astronomy, San Jose State University, One Washington Square, San Jose, CA 95192, USA
²⁷ Department of Astronomy, Stockholm University, AlbaNova, 106 91 Stockholm, Sweden
²⁸ California Institute of Technology, Cahill Center for Astronomy and Astrophysics, MS 301-17, Pasadena, CA 91125, USA
²⁹ University of Western Ontario, Department of Physics & Astronomy, London, Ontario, N6A 3K7, Canada
³⁰ Department of Physics and Astronomy, Johns Hopkins University, 3400 North Charles Street, Baltimore, MD 21218, USA
³¹ Jet Propulsion Laboratory, California Institute of Technology, Pasadena, CA 91109, USA
³² Department of Physics and Astronomy, University of Calgary, Calgary, T2N 1N4, AB, Canada
³³ Instituto de RadioAstronomía Milimétrica, Avenida Divina Pastora, 7, Núcleo Central E 18012 Granada, Spain
³⁴ Kapteyn Astronomical Institute, University of Groningen, PO Box 800, 9700 AV, Groningen, The Netherlands
³⁵ KOSMA, I. Physik. Institut, Universität zu Köln, Zülpicher Str. 77, 50937 Köln, Germany
³⁶ Atacama Large Millimeter/Submillimeter Array, Joint ALMA Office, Santiago, Chile

Received: 31 May 2010
Accepted: 13 July 2010

Abstract

“Water In Star-forming regions with Herschel” (WISH) is a key programme dedicated to studying the role of water and related species during the star-formation process and constraining the physical and chemical properties of young stellar objects. The Heterodyne Instrument for the Far-Infrared (HIFI) on the Herschel Space Observatory observed three deeply embedded protostars in the low-mass star-forming region NGC 1333 in several H₂¹⁶O, H₂¹⁸O, and CO transitions. Line profiles are resolved for five H₂¹⁶O transitions in each source, revealing them to be surprisingly complex. The line profiles are decomposed into broad (>20 km s^-1), medium-broad (~5-10 km s^-1), and narrow (<5 km s^-1) components. The H₂¹⁸O emission is only detected in broad 1₁₀–1₀₁ lines (>20 km s^-1), indicating that its physical origin is the same as for the broad H₂¹⁶O component. In one of the sources, IRAS4A, an inverse P Cygni profile is observed, a clear sign of infall in the envelope. From the line profiles alone, it is clear that the bulk of emission arises from shocks, both on small (1000 AU) and large scales along the outflow cavity walls (~10 000 AU). The H₂O line profiles are compared to CO line profiles to constrain the H₂O abundance as a function of velocity within these shocked regions. The H₂O/CO abundance ratios are measured to be in the range of ~0.1-1, corresponding to H₂O abundances of ~10^-5–10^-4 with respect to H₂. Approximately 5–10% of the gas is hot enough for all oxygen to be driven into water in warm post-shock gas, mostly at high velocities.