Letter to the Editor

Sensitive limits on the abundance of cold water vapor in the DM Tauri protoplanetary disk^*

¹ Department of Astronomy, The University of Michigan, 500 Church Street, Ann Arbor, MI 48109-1042, USA e-mail: ebergin@umich.edu
² Leiden Observatory, Leiden University, PO Box 9513, 2300 RA Leiden, The Netherlands
³ Max Planck Institut für Extraterrestrische Physik, Giessenbachstrasse 1, 85748 Garching, Germany
⁴ California Institute of Technology, Cahill Center for Astronomy and Astrophysics, MS 301-17, Pasadena, CA 91125, USA
⁵ California Institute of Technology, Division of Geological and Planetary Sciences, MS 150-21, Pasadena, CA 91125, USA
⁶ Centro de Astrobiología. Departamento de Astrofísica, CSIC-INTA, Carretera de Ajalvir, Km 4, Torrejón de Ardoz, 28850 Madrid, Spain
⁷ Astronomical Institute Anton Pannekoek, University of Amsterdam, Kruislaan 403, 1098 SJ Amsterdam, The Netherlands
⁸ Department of Astrophysics/IMAPP, Radboud University Nijmegen, PO Box 9010, 6500 GL Nijmegen, The Netherlands
⁹ Harvard-Smithsonian Center for Astrophysics, 60 Garden Street, MS 42, Cambridge, MA 02138, USA
¹⁰ Department of Physics and Astronomy, Johns Hopkins University, 3400 North Charles Street, Baltimore, MD 21218, USA
¹¹ European Southern Observatory, Karl-Schwarzschild-Str. 2, 85748 Garching, Germany
¹² Jet Propulsion Laboratory, California Institute of Technology, Pasadena, CA 91109, USA
¹³ Observatorio Astronómico Nacional (IGN), Calle Alfonso XII 3, 28014 Madrid, Spain
¹⁴ INAF - Istituto di Fisica dello Spazio Interplanetario, Area di Ricerca di Tor Vergata, via Fosso del Cavaliere 100, 00133 Roma, Italy
¹⁵ INAF - Osservatorio Astrofisico di Arcetri, Largo E. Fermi 5, 50125 Firenze, Italy
¹⁶ Institute of Astronomy, ETH Zurich, 8093 Zurich, Switzerland
¹⁷ Department of Radio and Space Science, Chalmers University of Technology, Onsala Space Observatory, 439 92 Onsala, Sweden
¹⁸ Université de Bordeaux, Laboratoire d'Astrophysique de Bordeaux, France; CNRS/INSU, UMR 5804, Floirac, France
¹⁹ School of Physics and Astronomy, University of Leeds, Leeds LS2 9JT, UK
²⁰ Department of Physics and Astronomy, Denison University, Granville, OH, 43023, USA
²¹ LERMA and UMR 8112 du CNRS, Observatoire de Paris, 61 Av. de l'Observatoire, 75014 Paris, France
²² University of Waterloo, Department of Physics and Astronomy, Waterloo, Ontario, Canada
²³ Observatorio Astronómico Nacional, Apartado 112, 28803 Alcalá de Henares, Spain
²⁴ INAF - Osservatorio Astronomico di Roma, 00040 Monte Porzio catone, Italy
²⁵ SRON Netherlands Institute for Space Research, PO Box 800, 9700 AV, Groningen, The Netherlands
²⁶ National Research Council Canada, Herzberg Institute of Astrophysics, 5071 West Saanich Road, Victoria, BC V9E 2E7, Canada
²⁷ Department of Physics and Astronomy, University of Victoria, Victoria, BC V8P 1A1, Canada
²⁸ Centre for Star and Planet Formation, Natural History Museum of Denmark, University of Copenhagen, Øster Voldgade 5-7, 1350 Copenhagen K., Denmark
²⁹ Department of Astronomy, Stockholm University, AlbaNova, 106 91 Stockholm, Sweden
³⁰ The University of Western Ontario, Department of Physics and Astronomy, London, Ontario, N6A 3K7, Canada
³¹ Max-Planck-Institut für Radioastronomie, Auf dem Hügel 69, 53121 Bonn, Germany
³² Department of Physics and Astronomy, University of Calgary, Calgary, T2N 1N4, AB, Canada
³³ Instituto de Radioastronomía Milimétrica (IRAM), Avenida Divina Pastora 7, Núcleo Central, 18012 Granada, Spain
³⁴ Kapteyn Astronomical Institute, University of Groningen, PO Box 800, 9700 AV, Groningen, The Netherlands
³⁵ Max-Planck-Insitut für Sonnensystemforschung, 37191 Katlenburg-Lindau, Germany
³⁶ KOSMA, I. Physik. Institut, Universität zu Köln, Zülpicher Str. 77, D 50937 Köln, Germany
³⁷ N. Copernicus Astronomical Center, Rabianska 8, 87-100, Torun, Poland

Received: 31 May 2010
Accepted: 26 June 2010

Abstract

We performed a sensitive search for the ground-state emission lines of ortho- and para-water vapor in the DM Tau protoplanetary disk using the Herschel/HIFI instrument. No strong lines are detected down to 3σ levels in 0.5 km s^-1 channels of 4.2 mK for the 1₁₀–1₀₁ line and 12.6 mK for the 1₁₁–0₀₀ line. We report a very tentative detection, however, of the 1₁₀–1₀₁ line in the wide band spectrometer, with a strength of T_mb = 2.7 mK, a width of 5.6 km s^-1 and an integrated intensity of 16.0 mK km s^-1. The latter constitutes a 6σ detection. Regardless of the reality of this tentative detection, model calculations indicate that our sensitive limits on the line strengths preclude efficient desorption of water in the UV illuminated regions of the disk. We hypothesize that more than 95–99% of the water ice is locked up in coagulated grains that have settled to the midplane.