Letter to the Editor

SPIRE spectroscopy of the prototypical Orion Bar photodissociation region^*

¹ Institut d'Astrophysique Spatiale, UMR 8617, CNRS/Université Paris-Sud 11, 91405 Orsay, France e-mail: emilie.habart@ias.u-psud.fr
² 
Laboratoire d'Astrophysique de Marseille (UMR 6110 CNRS & Université de Provence), 38 rue F. Joliot-Curie, 13388 Marseille Cedex 13, France
³ 
Institute for Space Imaging Science, University of Lethbridge, Lethbridge, Canada
⁴ 
The Rutherford Appleton Laboratory, Chilton, Didcot OX11 0QX, UK
⁵ 
 CESR, Université de Toulouse, UPS, CESR, 9 Av. du colonel Roche, 31028 Toulouse Cedex 4, France
⁶ CNRS, UMR5187, 31028 Toulouse, France
⁷ 
Department of Physics and Astronomy, Cardiff University, Cardiff, UK
⁸ 
CEA, Laboratoire AIM, Irfu/SAp, Orme des Merisiers, 91191 Gif-sur-Yvette, France
⁹ Canadian Institute for Theoretical Astrophysics, Toronto, Ontario, M5S 3H8, Canada
¹⁰ CNRS/INSU, Laboratoire d'Astrophysique de Bordeaux, UMR 5804, BP 89, 33271 Floirac Cedex, France
¹¹ 
University of California, Radio Astronomy Laboratory, Berkeley, 601 Campbell Hall, US Berkeley CA 94720-3411, USA
¹² 
Institut de Radioastronomie Millimétrique (IRAM), 300 rue de la Piscine, 38406 Saint-Martin-d'Hères, France
¹³ 
Joint Astronomy Centre, University Park, Hilo, USA
¹⁴ 
Blue Sky Spectrosocpy Inc, Lethbridge, Canada
¹⁵ National Astronomical Observatories, PR China
¹⁶ 
Istituto di Fisica dello Spazio Interplanetario, INAF, via del Fosso del Cavaliere 100, 00133 Roma, Italy
¹⁷ 
NASA - Goddard SFC, USA
¹⁸ 
Department of Physics & Astronomy, The Open University, Milton Keynes MK7 6AA, UK

Received: 31 March 2010
Accepted: 14 May 2010

Abstract

Aims. We present observations of the Orion Bar photodissociation region (PDR) obtained with the SPIRE instrument on-board Herschel.

Methods. We obtained SPIRE Fourier-transform spectrometer (FTS) sparse sampled maps of the Orion bar.

Results. The FTS wavelength coverage and sensitivity allow us to detect a wealth of rotational lines of CO (and its isotopologues), fine structure lines of C and N⁺, and emission lines from radicals and molecules such as CH⁺, CH, H₂O or H₂S. For species detected from the ground, our estimates of the column densities agree with previously published values. The comparison between ¹²CO and ¹³CO maps shows particularly the effects of optical depth and excitation in the molecular cloud. The distribution of the ¹²CO and ¹³CO lines with upper energy levels indicates the presence of warm (~100–150 K) CO. This warm CO component is a significant fraction of the total molecular gas, confirming previous ground based studies.