Letter to the Editor

The methanol lines and hot core of OMC2-FIR4, an intermediate-mass protostar, with Herschel/HIFI^*

¹ Astronomical Institute “Anton Pannekoek”, University of Amsterdam, Amsterdam, The Netherlands

² Department of Astrophysics/IMAPP, Radboud University Nijmegen, Nijmegen, The Netherlands

³ Laboratoire d'Astrophysique de Grenoble, UMR 5571-CNRS, Université Joseph Fourier, Grenoble, France

⁴ SRON Netherlands Institute for Space Research, Groningen, The Netherlands

⁵ Kapteyn Astronomical Institute, University of Groningen, The Netherlands

⁶ Centre d'Étude Spatiale des Rayonnements, Université Paul Sabatier, Toulouse, France

⁷ CNRS/INSU, UMR 5187, Toulouse, France

⁸ Université de Bordeaux, Laboratoire d'Astrophysique de Bordeaux, Floirac, France

⁹ CNRS/INSU, UMR 5804, Floirac Cedex, France

¹⁰ IGN Observatorio Astronómico Nacional, Alcalá de Henares, Spain
¹¹ Centro de Astrobiologìa, CSIC-INTA, Madrid, Spain

¹² Infared Processing and Analysis Center, Caltech, Pasadena, USA

¹³ California Institute of Technology, Pasadena, USA

¹⁴ INAF - Istituto di Fisica dello Spazio Interplanetario, Roma, Italy

¹⁵ Department of Astronomy, University of Michigan, Ann Arbor, USA

¹⁶ Laboratoire d'Études du Rayonnement et de la Matière en Astrophysique, UMR 8112 CNRS/INSU, OP, ENS, UPMC, UCP, Paris, France

¹⁷ School of Physics and Astronomy, University of Leeds, Leeds, UK

¹⁸ INAF Osservatorio Astrofisico di Arcetri, Florence, Italy

¹⁹ Max-Planck-Institut für Radioastronomie, Bonn, Germany

²⁰ Jet Propulsion Laboratory, Caltech, Pasadena, CA 91109, USA

²¹ Ohio State University, Columbus, OH, USA
²² Max-Planck-Institut für Astronomie, Heidelberg, Germany

²³ Harvard-Smithsonian Center for Astrophysics, Cambridge MA, USA

²⁴ INAF - Osservatorio Astronomico di Roma, Monte Porzio Catone, Italy

²⁵ Physikalisches Institut, Universität zu Köln, Köln, Germany

²⁶ Institut de RadioAstronomie Millimétrique, Grenoble, France

²⁷ Leiden Observatory, Leiden University, Leiden, The Netherlands


Received: 31 May 2010
Accepted: 29 July 2010

Abstract

In contrast with numerous studies on the physical and chemical structure of low- and high-mass protostars, much less is known about their intermediate-mass counterparts, a class of objects that could help to elucidate the mechanisms of star formation on both ends of the mass range. We present the first results from a rich HIFI spectral dataset on an intermediate-mass protostar, OMC2-FIR4, obtained in the CHESS (Chemical HErschel Survey of Star forming regions) key programme. The more than 100 methanol lines detected between 554 and 961 GHz cover a range in upper level energy of 40 to 540 K. Our physical interpretation focusses on the hot core, but likely the cold envelope and shocked regions also play a role in reality, because an analysis of the line profiles suggests the presence of multiple emission components. An upper limit of 10^-6 is placed on the methanol abundance in the hot core, using a population diagram, large-scale source model and other considerations. This value is consistent with abundances previously seen in low-mass hot cores. Furthermore, the highest energy lines at the highest frequencies display asymmetric profiles, which may arise from infall around the hot core.