Letter to the Editor
Water abundance variations around high-mass protostars: HIFI observations of the DR21 region*
SRON Netherlands Institute for Space Research, Landleven 12, 9747 AD Groningen, The Netherlands e-mail: firstname.lastname@example.org
2 Kapteyn Institute, University of Groningen, The Netherlands
3 Laboratoire d'Astrophysique de Bordeaux, Floirac, France
4 Max-Planck-Institut für Radioastronomie, Bonn, Germany
5 Denison University, Granville OH, USA
6 Harvard-Smithsonian Center for Astrophysics, Cambridge, USA
7 Sterrewacht, Universiteit Leiden, The Netherlands
8 MPI für Extraterrestrische Physik, Garching, Germany
9 Institute of Astronomy, ETH Zürich, 8093 Zürich, Switzerland
10 School of Physics and Astronomy, University of Leeds, UK
11 Herzberg Institute of Astrophysics, Victoria, Canada
12 Dept. of Physics and Astronomy, University of Victoria, Canada
13 Chalmers University of Technology, 41296 Göteborg, Sweden
14 Observatorio Astronómico Nacional, Alcalá de Henares, Spain
15 INAF – Istituto di Fisica dello Spazio Interplanetario, Roma, Italy
16 Dept. of Astronomy, University of Michigan, Ann Arbor, USA
17 California Institute of Technology, Pasadena CA 91125, USA
18 CAB, INTA-CSIC, Torrejón de Ardoz, Spain
19 Observatoire de Paris-Meudon, Meudon, France
20 University of Amsterdam, The Netherlands
21 LERMA and UMR 8112 du CNRS, Observatoire de Paris, France
22 Dept. of Physics and Astronomy, University of Waterloo, Canada
23 Joint ALMA Observatory, Santiago, Chile
24 Centre for Star and Planet Formation, U. of Copenhagen, Denmark
25 Department of Astronomy, Stockholm University, Sweden
26 Johns Hopkins University, Baltimore, USA
27 KOSMA, I. Physik. Institut, Universität zu Köln, Germany
28 JPL, California Institute of Technology, Pasadena, CA 91109, USA
29 Dept. of Physics and Astronomy, University of Calgary, Canada
30 CESR, Université de Toulouse, France
31 European Space Astronomy Centre, ESA, Madrid, Spain
Accepted: 20 April 2010
Context. Water is a key molecule in the star formation process, but its spatial distribution in star-forming regions is not well known.
Aims. We study the distribution of dust continuum and H2O and 13CO line emission in DR21, a luminous star-forming region with a powerful outflow and a compact H ii region.
Methods. Herschel-HIFI spectra near 1100 GHz show narrow 13CO 10–9 emission and H2O 111–000 absorption from the dense core and broad emission from the outflow in both lines. The H2O line also shows absorption by a foreground cloud known from ground-based observations of low-J CO lines.
Results. The dust continuum emission is extended over 36” FWHM, while the 13CO and H2O lines are confined to ≈24” or less. The foreground absorption appears to peak further North than the other components. Radiative transfer models indicate very low abundances of ~2×10-10 for H2O and ~8×10-7 for 13CO in the dense core, and higher H2O abundances of ~4×10-9 in the foreground cloud and ~7×10-7 in the outflow.
Conclusions. The high H2O abundance in the warm outflow is probably due to the evaporation of water-rich icy grain mantles, while the H2O abundance is kept down by freeze-out in the dense core and by photodissociation in the foreground cloud.
Key words: ISM: molecules / stars: formation / astrochemistry / ISM: individual objects: DR21
© ESO, 2010