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Astron. Astrophys. 315, L305-L308 (1996)

Infrared spectrophotometry of NGC 7023 with ISOCAM*

D. Cesarsky1, J. Lequeux2, A. Abergel1, M. Perault1, E. Palazzi3, S. Madden4, and D. Tran4

1 Institut d'Astrophysique Spatiale, Bat. 121, Université Paris XI, F-91450 Orsay Cedex, France
2 Observatoire de Paris, 61 Av. de l'Observatoire, F-75014 Paris, France
3 Istituto TESRE/CNR, via Gobetti 101, I-40129 Bologna, Italy,
4 SAp/DAPNIA/DSM, CEA-Saclay, F-91191 Gif-sur-Yvette, France

Received 16 July 1996 / Accepted 20 August 1996

Abstract. We present spectrophotometric observations of the reflection nebula NGC7023  obtained with the ISOCAM Circular Variable Filter (CVF) in the spectral range 5.15 to 16.5 img2.gifm. Maps in the 16 img2.gifm continuum emission and in the Unidentified Infrared Bands (UIBs) have been obtained. The continuum emission peaks at the dense interface between the surrounding molecular cloud and the inner photodissociated region. The whole spectrum (UIBs and continuum) becomes systematically harder closer to the exciting star. Our observations show that it is entirely due to the same category of carriers, probably PAHs heated transiently by single photons, and that the systematic spectral changes inside NGC7023  are due to changes in the size distribution or/and ionization degree of these particles.

Key words: ISM: NGC7023  - ISM: dust - ISM: molecules - ISM: reflection nebulae - infrared: ISM: lines and bands - infrared: ISM: continuum

* ISO is an ESA project with instruments funded by ESA Member States (especially the PI countries: France, Germany, the Netherlands and the United Kingdom) and with the participation of ISAS and NASA.

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