Letter to the Editor

The distribution of water in the high-mass star-forming region NGC 6334 I ^*,**

¹ California Institute of Technology, Pasadena, USA e-mail: emprecht@caltech.edu
² Physikalisches Institut, Universität zu Köln, Köln, Germany
³ Max-Planck-Institut für Radioastronomie, Bonn, Germany
⁴ SRON, Groningen, The Netherlands
⁵ Laboratoire d'Astrophysique de Grenoble, UMR 5571-CNRS, Université Joseph Fourier, Grenoble, France
⁶ Université de Bordeaux, Laboratoire d'Astrophysique de Bordeaux, France; CNRS/INSU, UMR 5804, Floirac, France
⁷ INAF - Istituto di Fisica dello Spazio Interplanetario, Roma, Italy
⁸ Department of Astronomy, University of Michigan, Ann Arbor, USA
⁹ Infared Processing and Analysis Center, Caltech, Pasadena, USA
¹⁰ CESR, Université Toulouse 3 and CNRS, Toulouse, France
¹¹ Observatoire de Paris-Meudon, LERMA UMR CNRS 8112, Meudon, France
¹² School of Physics and Astronomy, University of Leeds, Leeds UK
¹³ Centro de Astrobiologìa, CSIC-INTA, Madrid, Spain
¹⁴ INAF Osservatorio Astrofisico di Arcetri, Florence, Italy
¹⁵ Astronomical Institute “Anton Pannekoek”, University of Amsterdam, Amsterdam, The Netherlands
¹⁶ Department of Astrophysics/IMAPP, Radboud University Nijmegen, Nijmegen, The Netherlands
¹⁷ IGN Observatorio Astronómico Nacional, Alcalá de Henares, Spain
¹⁸ Jet Propulsion Laboratory, Caltech, Pasadena, CA 91109, USA
¹⁹ Max-Planck-Institut fur Astronomie, Heidelberg, Germany
²⁰ Ohio State University, Columbus, OH, USA
²¹ Max-Planck-Institut fur Sonnenphysikforschung, Lindau, Germany
²² Center for Astrophysics, Cambridge MA, USA
²³ Johns Hopkins University, Baltimore MD, USA
²⁴ INAF - Osservatorio Astronomico di Roma, Monte Porzio Catone, Italy
²⁵ Institut de RadioAstronomie Millimétrique, Grenoble, France
²⁶ Leiden Observatory, Leiden University, Leiden, The Netherlands
²⁷ Department of Physics and Astronomy, University College London, London, UK

Received: 30 May 2010
Accepted: 23 July 2010

Abstract

Aims. We present observations of twelve rotational transitions of H₂¹⁶O, H₂¹⁸O, and H₂¹⁷O toward the massive star-forming region NGC 6334 I, carried out with Herschel/HIFI as part of the guaranteed time key program Chemical HErschel Surveys of Star forming regions (CHESS). We analyze these observations to obtain insights into physical processes in this region.

Methods. We identify three main gas components (hot core, cold foreground, and outflow) in NGC 6334 I and derive the physical conditions in these components.

Results. The hot core, identified by the emission in highly excited lines, shows a high excitation temperature of ~200 K, whereas water in the foreground component is predominantly in the ortho- and para- ground states. The abundance of water varies between 4 × 10^-5 (outflow) and 10^-8 (cold foreground gas). This variation is most likely due to the freeze-out of water molecules onto dust grains. The H₂¹⁸O/H₂¹⁷O abundance ratio is 3.2, which is consistent with the ¹⁸O/¹⁷O ratio determined from CO isotopologues. The ortho/para ratio in water appears to be relatively low (1.6±1) in the cold, quiescent gas, but close to the equilibrium value of three in the warmer outflow material (2.5±0.8).