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Astron. Astrophys. 349, 253-258 (1999)

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High resolution Fourier transform spectroscopy of H2 IR emission in NGC 7023 *

J.L. Lemaire 1,2, D. Field 3, J.P. Maillard 4, G. Pineau des Forêts 5, E. Falgarone 6, F.P. Pijpers 7, M. Gerin 6 and F. Rostas 5

1 Observatoire de Paris-Meudon, F-92195 Meudon Principal Cedex, France
2 UMR8588 du CNRS, Université de Cergy-Pontoise, F-95806 Cergy Cedex, France
3 Institute for Storage Ring Facilities, University of Aarhus, DK-8000 Aarhus C, Denmark
and UMR8588 du CNRS, Observatoire de Paris-Meudon
4 UPR341 du CNRS, Institut d'Astrophysique, 98bis, Boulevard Arago, F-75014 Paris, France
5 UMR8631 du CNRS, Observatoire de Paris-Meudon, F-92195 Meudon Principal Cedex, France
6 UMR8540 du CNRS, Ecole Normale Supérieure, 24 Rue Lhomond, F-75231 Paris Cedex 05, France
7 Theoretical Astrophysics Centre, University of Aarhus, DK-8000 Aarhus C, Denmark

Received 22 February 1999 / Accepted 22 June 1999


A Fourier transform spectrum at a resolution of [FORMULA] 125,000 has been recorded of molecular hydrogen emission in the reflection nebula NGC 7023, in the S(1) v=1-0 line at 2.121 µm for a region 5 arcsec in diameter. The line is resolved and the derived linewidth corresponds to a kinetic temperature of 500[FORMULA] 70 K, if all motions are thermal. Comparison with data for HI, CI, CII and CO shows that there is a velocity gradient in the molecular material in the photodissociation region, demonstrating the motion of the photodissociation front relative to the molecular cloud. Models of the photodissociation region experience only limited success in reproducing the known brightness of the H2 emission in conjunction with the kinetic temperature determined here.

Key words: ISM: clouds – ISM: individual objects: – ISM: kinematics and dynamics – ISM: lines and bands – ISM: molecules – ISM: reflection nebulae

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

Send offprint requests to: D. Field

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© European Southern Observatory (ESO) 1999

Online publication: August 25, 1999