EDP Sciences Journals List
Advanced Search
Subscriber Authentication Point
Home All issues Volume 389/1 Article
Free access article

Issue A&A
Volume 389, Number 1, July I 2002
Page(s) 239 - 251
Section Diffuse matter in space
DOI http://dx.doi.org/10.1051/0004-6361:20020324



A&A 389, 239-251 (2002)
DOI: 10.1051/0004-6361:20020324

Evolution of very small particles in the southern part of Orion B observed by ISOCAM

A. Abergel1, J. P. Bernard1, F. Boulanger1, D. Cesarsky1, 2, E. Falgarone3, A. Jones1, M.-A. Miville-Deschenes1, 3, M. Perault3, J.-L. Puget1, M. Huldtgren4, A. A. Kaas4, L. Nordh4, G. Olofsson4, P. André5, S. Bontemps6, M. M. Casali7, C. J. Cesarsky5, M. E. Copet8, J. Davies9, T. Montmerle5, P. Persi10 and F. Sibille11

1  Institut d'Astrophysique Spatiale, Université Paris-Sud, Bât. 121, 91405 Orsay Cedex, France
2  Max Planck Institut fur extraterrestrische Physik, 85741 Garching, Germany
3  Radioastronomie Millimétrique, École Normale Supérieure, 24 rue Lhomond, 75005 Paris, France
4  Stockholm Observatory, 133 36 Saltsjöbaden, Sweden
5  Service d'Astrophysique, Centre d'Études de Saclay, 91191 Gif-Sur-Yvette Cedex, France
6  Observatoire de Bordeaux, BP 89, 33270 Floirac, France
7  Royal Observatory, Blackford Hill, Edinburgh, UK
8  DESPA, Observatoire de Paris-Meudon, 5 place Jules Janssen, 92195 Meudon Cedex, France
9  Joint Astronomy Center, 660 N. A'Ohoku Place, University Park, Hilo, HI 96720, USA
10  Istituto Astrofisica Spaziale, CNR, Area di Ricerca Tor Vergata, Roma, Italy
11  Observatoire de Lyon, 69230 Saint Genis Laval, France

(Received 30 July 2001 / Accepted 28 February 2002 )

Abstract
We present ISOCAM observations (5-18  $\mu$m) of the southern part of Orion B, including the reflection nebula NGC 2023 and the Horsehead nebula illuminated by the B star HD 37903 and the O star $\sigma$ Orionis, respectively. Due to the limited radiation field, the emission in these wavelengths is due to very small particles which are heated each time they absorb a UV photon. A filamentary structure is detected at small angular scales (down to the angular resolution of 6 $^{\prime\prime}$) on top of a smoother background. The particular case of the Horsehead nebula suggests that the filaments in general result from the illuminated surfaces of dense structures, while the smoother background comes from lower density matters probably ionised. Striking spatial variations of the infrared colour (5-8.5  $\mu$m/12-18  $\mu$m) are also detected. Spectroscopic observations show that they are due to variations of the intensity of the aromatic features (especially at $7.7~\mu$m) relative to a continuum emission increasing in intensity towards longer wavelengths. The contribution of the continuum relative to the aromatic features appears significantly higher at the illuminated surfaces of dense structures than in lower density matter. This effect could be the signature of the evolution of the very small particles from shielded molecular material to photo-dissociated and photo-ionised matter. We also show that size segregation due to grain dynamics in uni-directional radiation fields may play a major role.


Key words: methods: data analysis -- ISM: individual objects: Orion -- ISM: dust, extinction -- ISM: clouds -- ISM: structure -- infrared: ISM

Offprint request: A. Abergel, abergel@ias.u-psud.fr

SIMBAD Objects



© ESO 2002


What is OpenURL?

The OpenURL standard is a protocol for transmission of metadata describing the resource that you wish to access. An OpenURL link contains article metadata and directs it to the OpenURL server of your choice. The OpenURL server can provide access to the resource and also offer complementary services (specific search engine, export of references...). The OpenURL link can be generated by different means.
  • If your librarian has set up your subscription with an OpenURL resolver, OpenURL links appear automatically on the abstract pages.
  • You can define your own OpenURL resolver with your EDPS Account. In this case your choice will be given priority over that of your library.
  • You can use an add-on for your browser (Firefox or I.E.) to display OpenURL links on a page (see http://www.openly.com/openurlref/). You should disable this module if you wish to use the OpenURL server that you or your library have defined.