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Astron. Astrophys. 333, 280-286 (1998)

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New observations of H2 vibrational fluorescence in NGC 2023

D. Field * 1, J.L. Lemaire* 2, 3, G. Pineau des Forêts 2, M. Gerin 2, S. Leach 2, F. Rostas 2 and D. Rouan 2

1 Institute of Physics and Astronomy, University of Aarhus, DK-8000, Aarhus C, Denmark
and University of Bristol, School of Chemistry, Cantock's Close, Bristol BS8 1TS, UK
2 Observatoire de Paris-Meudon, F-92195 Meudon Cedex, France
3 Université de Cergy-Pontoise, F-95806 Cergy-Pontoise, France

Received 20 June 1997 / Accepted 18 December 1997


The Canada-France-Hawaii Telescope has been used to obtain images of NGC 2023 in the 1-0 S(1) and 1-0 S(2) lines of vibrationally excited H2 at 2.121 µm and 2.033 µm, respectively, at a spatial resolution of 0.8". Images show the presence of widespread emission exhibiting structure on a milliparsec scale. Using the latest estimates of the VUV field of the exciting star HD 37903, steady-state photodissociation region (PDR) models are able to reproduce the brightness of the observed emission with good accuracy, showing that the number density in the emitting region is [FORMULA] 105 cm-3.

Key words: ISM: individual objects: NGC 2023 – reflection nebulae; molecules – molecular processes – infrared: ism: lines; continuum

* Visiting astronomers (DF and JLL) at the Canada-France-Hawaii Telescope operated by the Conseil National de Recherche de Canada, the Conseil National de la Recherche Scientifique de France and the University of Hawaii

Send offprint requests to: D.Field (first address above)

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© European Southern Observatory (ESO) 1998

Online publication: April 15, 1998