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Astron. Astrophys. 354, L87-L91 (2000)

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Letter to the Editor

ISO observations of the reflection nebula Ced 201: evolution of carbonaceous dust  *

D. Cesarsky 1,2, J. Lequeux 3, C. Ryter 4 and M. Gérin 5

1 Université Paris XI, Institut d'Astrophysique Spatiale, Bat. 121, 91450 Orsay Cedex, France
2 Max Plank Institut für Extraterrestrische Physik, Postfach 1603, 85740 Garching, Germany
3 DEMIRM,Observatoire de Paris, 61 Avenue de l'Observatoire, 75014 Paris, France
4 SAp/DAPNIA/DSM, CEA-Saclay, 91191 Gif sur Yvette Cedex, France
5 Ecole Normale Supérieure, 24 Rue Lhomond, 75238 Paris Cedex 05, France

Received 30 November 1999 / Accepted 28 January 2000


We present spectrophotometric imaging mid-IR observations of the reflection nebula Ced 201. Ced 201 is a part of a molecular cloud illuminated by a B9.5V star moving through it at more than 12 km s-1. The spectra of Ced 201 give evidence for transformation of very small carbonaceous grains into the carriers of the Aromatic Infrared Bands (AIBs), due to the radiation field of the illuminating star and/or to shock waves created by its motion. These very small grains emit mainly very broad bands and a continuum. We suggest that they are present everywhere in the interstellar medium but can only be detected in the mid-IR under special circumstances such as those prevailing in this reflection nebula. The efficiency of energy conversion of stellar light into mid-infrared emission is 7.5% for both the very small grains and the AIB carriers, and the fraction of interstellar carbon locked in these emitters is approximately 15%.

Key words: ISM: individual objects: Ced 201 – ISM: dust, extinction – infrared: ISM: lines and bands

* Based on observations at the Cal Tech submillimeter observatory (CSO) and with ISO, 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.

Send offprint requests to: james.lequeux@obspm.fr

© European Southern Observatory (ESO) 2000

Online publication: February 25, 2000