Letter to the Editor

Herschel/HIFI spectroscopy of the intermediate mass protostar NGC 7129 FIRS 2 ^*,**

¹ National Research Council Canada, Herzberg Institute of Astrophysics, 5071 West Saanich Rd, Victoria, BC, V9E 2E7, Canada e-mail: doug.johnstone@nrc-cnrc.gc.ca
² Department of Physics & Astronomy, University of Victoria, Victoria, BC, V8P 1A1, Canada
³ Department of Physics and Astronomy, University of Waterloo, Waterloo, Ontario, N2L 3G, Canada
⁴ Department of Physics and Astronomy, the University of Western Ontario, London, Ontario, N6A 3K7, Canada
⁵ Leiden Observatory, Leiden University, PO Box 9513, 2300 RA Leiden, The Netherlands
⁶ Harvard-Smithsonian Center for Astrophysics, 60 Garden Street, MS 42, Cambridge, MA 02138, USA
⁷ Observatorio Astronómico Nacional (IGN), Apartado 1143, 28800 Alcalá de Henares, Spain
⁸ Department of Astrophysics, CAB, INTA-CSIC, Crta Torrejón a Ajalvir km 4, 28850 Torrejón de Ardoz, Spain
⁹ School of Physics and Astronomy, University of Leeds, Leeds LS2 9JT, UK
¹⁰ INAF - Osservatorio Astrofisico di Arcetri, Largo E. Fermi 5, 50125 Firenze, Italy
¹¹ Department of Physics and Astronomy, University of Calgary, Calgary, Alberta, Canada
¹² Max-Planck-Institut für extraterrestrische Physik, Garching, Germany
¹³ Institute of Astronomy, ETH Zürich, 8093 Zürich, Switzerland
¹⁴ INAF - Istituto di Fisica dello Spazio Interplanetario, Area di Ricerca di Tor Vergata, via Fosso del Cavaliere 100, 00133 Roma, Italy
¹⁵ Department of Astronomy, The University of Michigan, 500 Church Street, Ann Arbor, MI 48109-1042, USA
¹⁶ Department of Radio and Space Science, Chalmers University of Technology, Onsala Space Observatory, 439 92 Onsala, Sweden
¹⁷ California Institute of Technology, Division of Geological and Planetary Sciences, MS 150-21, Pasadena, CA 91125, USA
¹⁸ Université de Bordeaux, Laboratoire d'Astrophysique de Bordeaux, France; CNRS/INSU, UMR 5804, Floirac, France
¹⁹ Observatoire de Paris-Meudon, LERMA UMR CNRS 8112, 5 place Jules Janssen, 92195 Meudon Cedex, France
²⁰ Department of Molecular and Infrared Astrophysics, Consejo Superior de Investigaciones Cientificas, C/ Serrano 121, 28006 Madrid, Spain
²¹ Astronomical Institute Anton Pannekoek, University of Amsterdam, Kruislaan 403, 1098 SJ Amsterdam, The Netherlands
²² Department of Physics and Astronomy, Denison University, Granville, OH, 43023, USA
²³ LERMA and UMR 8112 du CNRS, Observatoire de Paris, 61 Av. de l'Observatoire, 75014 Paris, France
²⁴ Atacama Large Millimeter/Submillimeter Array, Joint ALMA Office, Santiago, Chile
²⁵ SRON Netherlands Institute for Space Research, Landleven 12, 9747 AD Groningen, The Netherlands
²⁶ Centre for Star and Planet Formation, Natural History Museum of Denmark, University of Copenhagen, Øster Voldgade 5-7, 1350 Copenhagen, Denmark
²⁷ Department of Astronomy, Stockholm University, AlbaNova, 106 91 Stockholm, Sweden
²⁸ Department of Physics and Astronomy, Johns Hopkins University, 3400 North Charles Street, Baltimore, MD 21218, USA
²⁹ Max-Planck-Institut für Radioastronomie, Auf dem Hügel 69, 53121 Bonn, Germany
³⁰ KOSMA, Physikalisches Institut, Universität zu Köln, Zülpicher Str. 77, 50937 Köln, Germany
³¹ Jet Propulsion Laboratory, California Institute of Technology, Pasadena, CA 91109, USA
³² Kapteyn Astronomical Institute, University of Groningen, PO Box 800, 9700 AV, Groningen, The Netherlands
³³ European Space Astronomy Centre, ESA, PO Box 78, 28691 Villanueva de la Cañada, Madrid, Spain

Received: 1 June 2010
Accepted: 23 July 2010

Abstract

Herschel/HIFI observations of water from the intermediate mass protostar NGC 7129 FIRS 2 provide a powerful diagnostic of the physical conditions in this star formation environment. Six spectral settings, covering four H₂¹⁶O and two H₂¹⁸O lines, were observed and all but one H₂¹⁸O line were detected. The four H₂¹⁶O  lines discussed here share a similar morphology: a narrower, ≈6 km s^-1, component centered slightly redward of the systemic velocity of NGC 7129 FIRS 2 and a much broader, ≈25 km s^-1 component centered blueward and likely associated with powerful outflows. The narrower components are consistent with emission from water arising in the envelope around the intermediate mass protostar, and the abundance of H₂O is constrained to ≈10^-7 for the outer envelope. Additionally, the presence of a narrow self-absorption component for the lowest energy lines is likely due to self-absorption from colder water in the outer envelope. The broader component, where the H₂O/CO relative abundance is found to be ≈0.2, appears to be tracing the same energetic region that produces strong CO emission at high J.