Letter to the Editor

Water in massive star-forming regions: HIFI observations of W3 IRS5^*

¹ Université de Bordeaux, Laboratoire d'Astrophysique de Bordeaux, France; CNRS/INSU, UMR 5804, Floirac, France e-mail: luisagustinchavarria@gmail.com
² SRON Netherlands Institute for Space Research, PO Box 800, 9700 AV, Groningen, The Netherlands
³ Kapteyn Astronomical Institute, University of Groningen, PO Box 800, 9700 AV, Groningen, The Netherlands
⁴ École des Mines de Nantes, 4 rue Alfred Kastler, 44300 Nantes, France
⁵ Max-Planck-Institut für Radioastronomie, Auf dem Hügel 69, 53121 Bonn, Germany
⁶ Leiden Observatory, Leiden University, PO Box 9513, 2300 RA Leiden, The Netherlands
⁷ Max Planck Institut für Extraterrestrische Physik, Giessenbachstrasse 1, 85748 Garching, Germany
⁸ Centro de Astrobiología. Departamento de Astrofísica. CSIC-INTA. Carretera de Ajalvir, Km 4, Torrejón de Ardoz, 28850 Madrid, Spain
⁹ Observatorio Astronómico Nacional (IGN), Calle Alfonso XII,3. 28014 Madrid, Spain
¹⁰ INAF – Istituto di Fisica dello Spazio Interplanetario, Area di Ricerca di Tor Vergata, via Fosso del Cavaliere 100, 00133 Roma, Italy
¹¹ Institute of Astronomy, ETH Zurich, 8093 Zurich, Switzerland
¹² Department of Astronomy, The University of Michigan, 500 Church Street, Ann Arbor, MI 48109-1042, USA
¹³ Department of Radio and Space Science, Chalmers University of Technology, Onsala Space Observatory, 439 92 Onsala, Sweden
¹⁴ California Institute of Technology, Division of Geological and Planetary Sciences, MS 150-21, Pasadena, CA 91125, USA
¹⁵ School of Physics and Astronomy, University of Leeds, Leeds LS2 9JT, UK
¹⁶ INAF – Osservatorio Astrofisico di Arcetri, Largo E. Fermi 5, 50125 Firenze, Italy
¹⁷ Astronomical Institute Anton Pannekoek, University of Amsterdam, Kruislaan 403, 1098 SJ Amsterdam, The Netherlands
¹⁸ Department of Astrophysics/IMAPP, Radboud University Nijmegen, PO Box 9010, 6500 GL Nijmegen, The Netherlands
¹⁹ Department of Physics and Astronomy, Denison University, Granville, OH 43023, USA
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 
MPI für Sonnensystemforschung, 37191 Katlenburg-Lindau, Germany
²⁵ National Research Council Canada, Herzberg Institute of Astrophysics, 5071 West Saanich Road, Victoria, BC V9E 2E7, Canada
²⁶ Department of Physics and Astronomy, University of Victoria, Victoria, BC V8P 1A1, Canada
²⁷ Centre for Star and Planet Formation, Natural History Museum of Denmark, University of Copenhagen, Øster Voldgade 5-7, 1350 Copenhagen K., Denmark
²⁸ Department of Astronomy, Stockholm University, AlbaNova, 106 91 Stockholm, Sweden
²⁹ California Institute of Technology, Cahill Center for Astronomy and Astrophysics, MS 301-17, Pasadena, CA 91125, USA
³⁰ The University of Western Ontario, Department of Physics and Astronomy, London, Ontario, N6A 3K7, Canada
³¹ Harvard-Smithsonian Center for Astrophysics, 60 Garden Street, MS 42, Cambridge, MA 02138, USA
³² Jet Propulsion Laboratory, California Institute of Technology, Pasadena, CA 91109, USA
³³ Department of Physics and Astronomy, University of Calgary, Calgary, T2N 1N4, AB, Canada
³⁴ Instituto de Radioastronomía Milimétrica (IRAM), Avenida Divina Pastora 7, Núcleo Central, 18012 Granada, Spain
³⁵ KOSMA, I. Physik. Institut, Universität zu Köln, Zülpicher Str. 77, 50937 Köln, Germany
³⁶ N. Copernicus Astronomical Center, Rabianska 8, 87-100, Torun, Poland

Received: 31 May 2010
Accepted: 20 July 2010

Abstract

We present Herschel observations of the water molecule in the massive star-forming region W3 IRS5. The o-H₂¹⁷O 1₁₀-1₀₁, p-H₂¹⁸O 1₁₁-0₀₀, p-H₂O 2₀₂-1₁₁, p-H₂O 1₁₁-0₀₀, o-H₂O 2₂₁-2₁₂, and o-H₂O 2₁₂-1₀₁ lines, covering a frequency range from 552 up to 1669 GHz, have been detected at high spectral resolution with HIFI. The water lines in W3 IRS5 show well-defined high-velocity wings that indicate a clear contribution by outflows. Moreover, the systematically blue-shifted absorption in the H₂O lines suggests expansion, presumably driven by the outflow. No infall signatures are detected. The p-H₂O 1₁₁-0₀₀ and o-H₂O 2₁₂-1₀₁ lines show absorption from the cold material (T ~ 10 K) in which the high-mass protostellar envelope is embedded. One-dimensional radiative transfer models are used to estimate water abundances and to further study the kinematics of the region. We show that the emission in the rare isotopologues comes directly from the inner parts of the envelope (T ≳ 100 K) where water ices in the dust mantles evaporate and the gas-phase abundance increases. The resulting jump in the water abundance (with a constant inner abundance of 10^-4) is needed to reproduce the o-H₂¹⁷O 1₁₀-1₀₁ and p-H₂¹⁸O 1₁₁-0₀₀ spectra in our models. We estimate water abundances of 10^-8 to 10^-9 in the outer parts of the envelope (T ≲ 100 K). The possibility of two protostellar objects contributing to the emission is discussed.