Letter to the Editor

Herschel-PACS spectroscopy of the intermediate mass protostar NGC 7129 FIRS 2 ^*,**

M. Fich¹, D. Johnstone^2,3, T. A. van Kempen^4,5, C. McCoey^1,6, A. Fuente⁷, P. Caselli^8,9, L. E. Kristensen³, R. Plume¹⁰, J. Cernicharo¹¹, G. J. Herczeg¹², E. F. van Dishoeck^4,12, S. Wampfler¹³, P. Gaufre¹⁴, J. J. Gill¹⁵, H. Javadi¹⁵, M. Justen¹⁶, W. Laauwen¹⁷, W. Luinge¹⁷, V. Ossenkopf¹⁶, J. Pearson¹⁵, R. Bachiller⁷, A. Baudry¹⁴, M. Benedettini^18,19, E. Bergin¹⁹, A. O. Benz¹³, P. Bjerkeli²⁰, G. Blake²¹, S. Bontemps¹⁴, J. Braine¹⁴, S. Bruderer¹³, C. Codella¹⁸, F. Daniel^22,23, A. M. di Giorgio¹⁸, C. Dominik²⁴, S. D. Doty²⁵, P. Encrenaz²⁶, T. Giannini¹⁸, J. R. Goicoechea¹¹, Th. de Graauw¹⁷, F. Helmich¹⁷, F. Herpin¹⁴, M. R. Hogerheijde⁴, T. Jacq¹⁴, J. K. Jørgensen²⁷, B. Larsson²⁸, D. Lis²¹, R. Liseau²⁰, M. Marseille¹⁷, G. Melnick⁴, B. Nisini¹⁸, M. Olberg²⁰, B. Parise^29,30, C. Risacher¹⁷, J. Santiago⁷, P. Saraceno¹⁸, R. Shipman¹⁷, M. Tafalla⁷, F. van der Tak^17,31, R. Visser⁴, F. Wyrowski²⁹ and U. A. Yıldız⁴

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

Received: 31 March 2010
Accepted: 15 May 2010

Abstract

Aims. We present preliminary results of the first Herschel spectroscopic observations of NGC 7129 FIRS2, an intermediate mass star-forming region. We attempt to interpret the observations in the framework of an in-falling spherical envelope.

Methods. The PACS instrument was used in line spectroscopy mode (R = 1000–5000) with 15 spectral bands between 63 and 185 μm. This provided good detections of 26 spectral lines seen in emission, including lines of H₂O, CO, OH, O I, and C II.

Results. Most of the detected lines, particularly those of H₂O and CO, are substantially stronger than predicted by the spherical envelope models, typically by several orders of magnitude. In this paper we focus on what can be learned from the detected CO emission lines.

Conclusions. It is unlikely that the much stronger than expected line emission arises in the (spherical) envelope of the YSO. The region hot enough to produce such high excitation lines within such an envelope is too small to produce the amount of emission observed. Virtually all of this high excitation emission must arise in structures such as as along the walls of the outflow cavity with the emission produced by a combination of UV photon heating and/or non-dissociative shocks.