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Issue
A&A
Volume 392, Number 2, September III 2002
Page(s) 691 - 698
Section Diffuse matter in space
DOI http://dx.doi.org/10.1051/0004-6361:20020942


A&A 392, 691-698 (2002)
DOI: 10.1051/0004-6361:20020942

Submillimeter dust emission of the M 17 complex measured with PRONAOS

X. Dupac1, M. Giard1, J.-P. Bernard1, 2, N. Boudet1, J.-M. Lamarre3, C. Mény1, F. Pajot2, É. Pointecouteau1, I. Ristorcelli1, G. Serra1, B. Stepnik2 and J.-P. Torre4

1  Centre d'Étude Spatiale des Rayonnements, 9 Av. du colonel Roche, BP 4346, 31028 Toulouse Cedex 4, France
2  Institut d'Astrophysique Spatiale, Campus d'Orsay, Bât. 121, 15 rue Clémenceau, 91405 Orsay Cedex, France
3  LERMA, Observatoire de Paris, 61 avenue de l'Observatoire, 75014 Paris, France
4  Service d'Aéronomie du CNRS, BP 3, 91371 Verrières-le-Buisson Cedex, France

(Received 15 January 2002 / Accepted 12 June 2002)

Abstract
We map a 50 $' \times 30'$ area in and around the M 17 molecular complex with the French submillimeter balloon-borne telescope PRONAOS, in order to better understand the thermal emission of cosmic dust and the structure of the interstellar medium. The PRONAOS-SPM instrument has an angular resolution of about 3 ', corresponding to a size of 2 pc at the distance of this complex, and a high sensitivity up to 0.8 MJy/sr. The observations are made in four wide submillimeter bands corresponding to effective wavelengths of 200  ${\mu}{\rm m}$, 260  ${\mu}{\rm m}$, 360  ${\mu}{\rm m}$ and 580  ${\mu}{\rm m}$. Using an improved map-making method for PRONAOS data, we map the M 17 complex and faint condensations near the dense warm core. We derive maps of both the dust temperature and the spectral index, which vary over a wide range, from about 10 K to 100 K for the temperature and from about 1 to 2.5 for the spectral index. We show that these parameters are anticorrelated, the cold areas (10-20 K) having a spectral index around 2, whereas the warm areas have a spectral index between 1 and 1.5. We discuss possible causes of this effect, and we propose an explanation involving intrinsic variations of the grain properties. Indeed, to match the observed spectra with two dust components having a spectral index equal to 2 leads to very large and unlikely amounts of cold dust. We also give estimates of the column densities and masses of the studied clumps. Three cold clumps (14-17 K) could be gravitationally unstable.


Key words: dust -- infrared: ISM: continuum -- ISM: clouds -- ISM: individual (M 17)

Offprint request: X. Dupac, dupac@cesr.fr

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