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Astron. Astrophys. 315, L185-L188 (1996)

ISOCAM observations of low-luminosity young stellar objects in the Chamaeleon dark clouds*

L. Nordh1, G. Olofsson1, A. Abergel2, Ph. Andr'e3, J. Blommaert4, S. Bontemps1, F. Boulanger2, M. Burgdorf4, C.J. C'esarsky3, D. C'esarsky2, E. Copet5, J. Davies6, E. Falgarone7, M. Huldtgren1, A.A. Kaas1, G. Lagache2, T. Montmerle3, M. Perault7, P. Persi8, T. Prusti4, J.L. Puget2, and F. Sibille9

1 Stockholm Observatory, S-133 36 Saltsjöbaden, Sweden (nordh@astro.su.se, olofsson@astro.su.se)
2 Institut dAstrophysique Spatiale, Universit'e Paris XI, Bât. 121, F-91405 Orsay Cedex, France
3 DAPNIA/SAp, C.E.A. Saclay, F-91191 Gif-Sur-Yvette Cedex, France
4 ISO, Villafranca del Castillo, ESA Satellite tracking station, P.O. Box 50727, E-28080 Madrid, Spain
5 DESPA, Observatoire de Paris-Meudon, 5 Place Jules Janssen, F-92195 Meudon Cedex, France
6 Joint Astronomy Centre, 660 N. A,Ohoku Place, University Park, Hilo, HI 96720, USA
7 ENS Radioastronomie, 24 rue Lhomond, F-75231 Paris Cedex 05, France
8 Instituto Astrofisica Spaziale, CNR, v. E. Fermi 21, I-00044 Frascati, Italy
9 Observatoire de Lyon, F-69230 Saint Genis Laval, France

Received 9 July 1996 / Accepted 29 August 1996

Abstract. We report the first results from an ISOCAM survey for low-luminosity, young stellar objects (YSOs) in nearby star formation regions. The present Letter concerns three regions within the Chamaeleon dark clouds, with a total area coverage of img1.gif 0.8 square degrees, representing 35% of the presently approved survey programme. The survey is conducted in two broad-band filters, LW2 (6.75 img2.gifm) and LW3 (15 img2.gifm), with a somewhat variable sensitivity limit in order to avoid saturation. For the nominal setup with 2.1 seconds integration time and 6 arcsec per pixel the detection limit is 1.9 mJy and 2.5 mJy in LW2 and LW3, respectively.

The Chamaeleon observations demonstrate that embedded YSOs can be effectively separated from background stars through distinctly different [15/6.75] colour indices. This allows us to identify 65 YSO candidates, of which more than 40% were not previously known. The observed LW3 luminosity function of the identified YSOs seems to be truncated by the sensitivity limit of the survey.

Key words: infrared: stars - stars: formation - stars: pre-main sequence - stars: luminosity function, mass function

* 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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