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Astron. Astrophys. 352, 277-286 (1999)

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Grain populations in the M 17 south-west star forming complex *

E. Crété 1, M. Giard 1, C. Joblin 1, I. Vauglin 2, A. Léger 3 and D. Rouan 4

1 Centre d'Etude Spatiale des Rayonnements, 9 av. du Colonel Roche, B.P. 4346, 31028 Toulouse Cedex 04, France
2 Observatoire de Lyon, 69561 Saint Genis Laval Cedex, France
3 Institut d'Astrophysique Spatiale, 91405 Orsay Cedex, France
4 Observatoire de Paris, 92195 Meudon Cedex, France

Received 10 May 1999 / Accepted 3 August 1999


The different spectral components of the 3-12[FORMULA]m dust emission are imaged in the M 17 south-west molecular cloud / HII region interface. The various images result from a combination of space borne (ISO) and ground based (CFHT) observations. A spatial correlation analysis shows that there are two main components, which correspond to the continuum (including broad features) and to the emission bands (3.3, 6.2, 7.7 and 11.3[FORMULA]m) respectively. The former peaks towards the HII region whereas the later dominates at the molecular cloud interface. This is consistent with a model which attributes the bands to PAH molecules and the continuum to very small grains. In the frame of the coal dust model, these observations put constraints on the properties of the grains, implying a band-to-continuum ratio which varies strongly with the excitation conditions. This analysis, which points out the signature of very small particles, does not favor one model relative to the other.

Key words: ISM: dust, extinction – ISM: clouds – ISM: individual objects: M 17 SW – infrared: ISM: lines and bands

* Based on observations with ISO, an ESA project with instruments funded by ESA Member States (especially the PI countries: France, Germany, the Netherlands and the United Kingdom) with the participation of ISAS and NASA. And based on observations with the C10 µ camera at the CHFT.

Send offprint requests to: Emmanuel.Crete@cesr.fr

© European Southern Observatory (ESO) 1999

Online publication: November 23, 1999