Letter to the Editor

Hydrides in young stellar objects: Radiation tracers in a protostar-disk-outflow system ^*,**

¹ Institute of Astronomy, ETH Zurich, 8093 Zurich, Switzerland e-mail: benz@astro.phys.ethz.ch
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 Institute of 4D Technologies, University of Applied Sciences NW, 5210 Windisch, Switzerland
⁵ Max-Planck-Institut für Radioastronomie, Auf dem Hügel 69, 53121 Bonn, Germany
⁶ Department of Physics and Astronomy, Denison University, Granville, OH, 43023, USA
⁷ SRON Netherlands Institute for Space Research, PO Box 800, 9700 AV, Groningen, The Netherlands
⁸ Kapteyn Astronomical Institute, University of Groningen, PO Box 800, 9700 AV, Groningen, The Netherlands
⁹ Laboratory for Electromagnetic Fields and Microwave Electronics, ETH Zurich, 8092 Zurich, Switzerland
¹⁰ Observatorio Astronómico Nacional (IGN), Calle Alfonso XII 3, 28014 Madrid, Spain
¹¹ Université de Bordeaux, Laboratoire d'Astrophysique de Bordeaux, France; CNRS/INSU, UMR 5804, Floirac, France
¹² INAF - Istituto di Fisica dello Spazio Interplanetario, Area di Ricerca di Tor Vergata, via Fosso del Cavaliere 100, 00133 Roma, Italy
¹³ Department of Astronomy, The University of Michigan, 500 Church Street, Ann Arbor, MI 48109-1042, USA
¹⁴ Department of Radio and Space Science, Chalmers University of Technology, Onsala Space Observatory, 439 92 Onsala, Sweden
¹⁵ California Institute of Technology, Division of Geological and Planetary Sciences, MS 150-21, Pasadena, CA 91125, USA
¹⁶ School of Physics and Astronomy, University of Leeds, Leeds LS2 9JT, UK
¹⁷ INAF - Osservatorio Astrofisico di Arcetri, Largo E. Fermi 5, 50125 Firenze, Italy
¹⁸ Centro de Astrobiología. Departamento de Astrofísica. CSIC-INTA. Carretera de Ajalvir, Km 4, Torrejón de Ardoz, 28850 Madrid, Spain.
¹⁹ Astronomical Institute Anton Pannekoek, University of Amsterdam, Kruislaan 403, 1098 SJ Amsterdam, The Netherlands
²⁰ Department of Astrophysics/IMAPP, Radboud University Nijmegen, PO Box 9010, 6500 GL Nijmegen, The Netherlands
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 National Research Council Canada, Herzberg Institute of Astrophysics, 5071 West Saanich Road, Victoria, BC V9E 2E7, Canada
²⁶ Department of Physics and Astronomy, University of Victoria, Victoria, BC V8P 1A1, Canada
²⁷ Centre for Star and Planet Formation, Natural History Museum of Denmark, University of Copenhagen, Øster Voldgade 5-7, 1350 Copenhagen K., Denmark
²⁸ Department of Astronomy, Stockholm University, AlbaNova, 106 91 Stockholm, Sweden
²⁹ California Institute of Technology, Cahill Center for Astronomy and Astrophysics, MS 301-17, Pasadena, CA 91125, USA
³⁰ The University of Western Ontario, Department of Physics and Astronomy, London, Ontario, N6A 3K7, Canada
³¹ Harvard-Smithsonian Center for Astrophysics, 60 Garden Street, MS 42, Cambridge, MA 02138, USA
³² Department of Physics and Astronomy, Johns Hopkins University, 3400 North Charles Street, Baltimore, MD 21218, USA
³³ KOSMA, I. Physik. Institut, Universität zu Köln, Zülpicher Str. 77, 50937 Köln, Germany
³⁴ Jet Propulsion Laboratory, California Institute of Technology, Pasadena, CA 91109, USA
³⁵ Department of Physics and Astronomy, University of Calgary, Calgary, T2N 1N4, AB, Canada
³⁶ Instituto de Radioastronomía Milimétrica (IRAM), Avenida Divina Pastora 7, Núcleo Central, 18012 Granada, Spain

Received: 31 May 2010
Accepted: 14 July 2010

Abstract

Context. Hydrides of the most abundant heavier elements are fundamental molecules in cosmic chemistry. Some of them trace gas irradiated by UV or X-rays.

Aims. We explore the abundances of major hydrides in W3 IRS5, a prototypical region of high-mass star formation.

Methods. W3 IRS5 was observed by HIFI on the Herschel Space Observatory with deep integration (2500 s) in 8 spectral regions.

Results. The target lines including CH, NH, H₃O⁺, and the new molecules SH⁺, H₂O⁺, and OH⁺ are detected. The H₂O⁺ and OH⁺ J = 1–0 lines are found mostly in absorption, but also appear to exhibit weak emission (P-Cyg-like). Emission requires high density, thus originates most likely near the protostar. This is corroborated by the absence of line shifts relative to the young stellar object (YSO). In addition, H₂O⁺ and OH⁺ also contain strong absorption components at a velocity shifted relative to W3 IRS5, which are attributed to foreground clouds.

Conclusions. The molecular column densities derived from observations correlate well with the predictions of a model that assumes the main emission region is in outflow walls, heated and irradiated by protostellar UV radiation.