Letter to the Editor

Herschel observations of deuterated water towards Sgr B2(M)^*

¹ Max-Planck-Institut für Radioastronomie, Auf dem Hügel 69, 53121 Bonn, Germany e-mail: ccomito@mpifr.de
² I. Physikalisches Institut, Universität zu Köln, Zülpicher Str. 77, 50937 Köln, Germany
³ California Institute of Technology, Cahill Center for Astronomy and Astrophysics 301-17, Pasadena, CA 91125, USA
⁴ Department of Astronomy, University of Michigan, 500 Church Street, Ann Arbor, MI 48109, USA
⁵ Centre d'étude Spatiale des Rayonnements, Université de Toulouse [UPS], 31062 Toulouse Cedex 9, France
⁶ CNRS/INSU, UMR 5187, 9 avenue du Colonel Roche, 31028 Toulouse Cedex 4, France
⁷ Laboratoire d'Astrophysique de l'Observatoire de Grenoble, BP 53, 38041 Grenoble, Cedex 9, France
⁸ Centro de Astrobiología (CSIC/INTA), Laboratiorio de Astrofísica Molecular, Ctra. de Torrejón a Ajalvir, km 4 28850, Torrejón de Ardoz, Madrid, Spain
⁹ LERMA, CNRS UMR8112, Observatoire de Paris and École Normale Supérieure, 24 Rue Lhomond, 75231 Paris Cedex 05, France
¹⁰ LPMAA, UMR7092, Université Pierre et Marie Curie, Paris, France
¹¹ LUTH, UMR8102, Observatoire de Paris, Meudon, France
¹² Jet Propulsion Laboratory, Caltech, Pasadena, CA 91109, USA
¹³ Departments of Physics, Astronomy and Chemistry, Ohio State University, Columbus, OH 43210, USA
¹⁴ National Research Council Canada, Herzberg Institute of Astrophysics, 5071 West Saanich Road, Victoria, BC V9E 2E7, Canada
¹⁵ Infrared Processing and Analysis Center, California Institute of Technology, MS 100-22, Pasadena, CA 91125, USA
¹⁶ Canadian Institute for Theoretical Astrophysics, University of Toronto, 60 St George St, Toronto, ON M5S 3H8, Canada
¹⁷ Harvard-Smithsonian Center for Astrophysics, 60 Garden Street, Cambridge MA 02138, USA
¹⁸ National University of Ireland Maynooth. Ireland
¹⁹ Department of Physics and Astronomy, Johns Hopkins University, 3400 North Charles Street, Baltimore, MD 21218, USA
²⁰ SRON Netherlands Institute for Space Research, PO Box 800, 9700 AV, Groningen, The Netherlands
²¹ Department of Physics and Astronomy, University of Calgary, 2500 University Drive NW, Calgary, AB T2N 1N4, Canada
²² Chalmers University of Technology, 412 96 Göteborg, Sweden
²³ N. Copernicus Astronomical Center, Rabianska 8, 87-100, Torun, Poland
²⁴ Department of Astronomy, Stockholm University, 106 91 Stockholm, Sweden

Received: 31 May 2010
Accepted: 26 July 2010

Abstract

Observations of HDO are an important complement for studies of water, because they give strong constraints on the formation processes – grain surfaces versus energetic process in the gas phase, e.g. in shocks. The HIFI observations of multiple transitions of HDO in Sgr B2(M) presented here allow the determination of the HDO abundance throughout the envelope, which has not been possible before with ground-based observations only. The abundance structure has been modeled with the spherical Monte Carlo radiative transfer code RATRAN, which also takes radiative pumping by continuum emission from dust into account. The modeling reveals that the abundance of HDO rises steeply with temperature from a low abundance (2.5 × 10^-11) in the outer envelope at temperatures below 100 K through a medium abundance (1.5 × 10^-9) in the inner envelope/outer core at temperatures between 100 and 200 K, and finally a high abundance (3.5 × 10^-9) at temperatures above 200 K in the hot core.