Herschel observations of EXtra-Ordinary Sources (HEXOS): Methanol as a probe of physical conditions in Orion KL^⋆

¹ Department of Astronomy, University of Michigan, 500 Church Street, Ann Arbor, MI 48109, USA
e-mail: shiya@umich.edu
² Jet Propulsion Laboratory, Caltech, Pasadena, CA 91109, USA
³ California Institute of Technology, Cahill Center for Astronomy and Astrophysics 301-17, Pasadena, CA 91125, USA
⁴ Max-Planck-Institut für Radioastronomie, Auf dem Hügel 69, 53121 Bonn, Germany
⁵ I. Physikalisches Institut, Universität zu Köln, Zülpicher Str. 77, 50937 Köln, Germany
⁶ California Institute of Technology, Division of Geological and Planetary Sciences, MS 150-21, Pasadena, CA 91125, USA
⁷ Centre d’étude Spatiale des Rayonnements, Université de Toulouse [UPS], 31062 Toulouse Cedex 9, France
⁸ CNRS/INSU, UMR 5187, 9 avenue du Colonel Roche, 31028 Toulouse Cedex 4, France
⁹ Laboratoire d’Astrophysique de l’Observatoire de Grenoble, BP 53, 38041 Grenoble, Cedex 9, France
¹⁰ Centro de Astrobiología (CSIC/INTA), Laboratiorio de Astrofísica Molecular, Ctra. de Torrejón a Ajalvir, km 4 28850, Torrejón de Ardoz, Madrid, Spain
¹¹ LERMA, CNRS UMR8112, Observatoire de Paris and École Normale Supérieure, 24 Rue Lhomond, 75231 Paris Cedex 05, France
¹² LPMAA, UMR7092, Université Pierre et Marie Curie, Paris, France
¹³ LUTH, UMR8102, Observatoire de Paris, Meudon, France
¹⁴ Departments of Physics, Astronomy and Chemistry, Ohio State University, Columbus, OH 43210, USA
¹⁵ National Research Council Canada, Herzberg Institute of Astrophysics, 5071 West Saanich Road, Victoria, BC V9E 2E7, Canada
¹⁶ Infrared Processing and Analysis Center, California Institute of Technology, MS 100-22, Pasadena, CA 91125, USA
¹⁷ Canadian Institute for Theoretical Astrophysics, University of Toronto, 60 St George St, Toronto, ON M5S 3H8, Canada
¹⁸ Harvard-Smithsonian Center for Astrophysics, 60 Garden Street, Cambridge MA 02138, USA
¹⁹ National University of Ireland Maynooth. Ireland
²⁰ Department of Physics and Astronomy, Johns Hopkins University, 3400 North Charles Street, Baltimore, MD 21218, USA
²¹ SRON Netherlands Institute for Space Research, PO Box 800, 9700 AV, Groningen, The Netherlands
²² Department of Physics and Astronomy, University of Calgary, 2500 University Drive NW, Calgary, AB T2N 1N4, Canada

Received: 28 May 2010
Accepted: 21 December 2010

Abstract

We have examined methanol emission from Orion KL withthe Herschel/HIFI instrument, and detected two methanol bands centered at 524 GHz and 1061 GHz. The 524 GHz methanol band (observed in HIFI band 1a) is dominated by the isolated ΔJ = 0, K = −4 → −3, v_t = 0 Q branch, and includes 25 E-type and 2 A-type transitions. The 1061 GHz methanol band (observed in HIFI band 4b) is dominated by the ΔJ = 0, K = 7 → 6, v_t = 0 Q branch transitions which are mostly blended. We have used the isolated E-type v_t = 0 methanol transitions to explore the physical conditions in the molecular gas. With HIFI’s high velocity resolution, the methanol emission contributed by different spatial components along the line of sight toward Orion KL (hot core, low velocity flow, and compact ridge) can be distinguished and studied separately. The isolated transitions detected in these bands cover a broad energy range (upper state energy ranging from 80 K to 900 K), which provides a unique probe of the thermal structure in each spatial component. The observations further show that the compact ridge is externally heated. These observations demonstrate the power of methanol lines as probes of the physical conditions in warm regions in close proximity to young stars.