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Astron. Astrophys. 336, 490-502 (1998)


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Brown dwarfs and very low-mass stars in the Pleiades cluster:
a deep wide-field imaging survey *

J. Bouvier 1, J.R. Stauffer 2, E.L. Martín 3, 4, D. Barrado y Navascués 3, B. Wallace 5 and V.J.S. Béjar 4

1 Laboratoire d'Astrophysique, Observatoire de Grenoble, Université Joseph Fourier, B.P. 53, F-38041 Grenoble Cedex 9, France (jbouvier@laog.obs.ujf-grenoble.fr, http://gag.observ-gr.fr/liens/starform/formation.html)
2 Harvard-Smithsonian Center for Astrophysics, 60 Garden Street, Cambridge, MA 02138, USA
3 University of California at Berkeley, 601 Campbell Hall, Berkeley, CA 94720, USA
4 Instituto de Astrofísica de Canarias, E-38200 La Laguna, Tenerife, Spain
5 University of Victoria, B.C., Canada

Received 20 March 1998 / Accepted 29 May 1998

Abstract

We have performed a deep, wide-field imaging survey of the Pleiades cluster (Melotte 22) in the R and I-bands to search for very low-mass stars and brown dwarfs. The survey extends over [FORMULA]2.5 square degrees around the cluster's center down to a [FORMULA]90% completeness limit of R[FORMULA]23 and I[FORMULA]22. We find 26 objects whose location in the (I, R-I) color-magnitude diagram is consistent with them being Pleiades members. Of these, 17 have extremely red (R-I) colors and low I luminosity, which make them prime brown dwarf candidates. We present the luminosity function of the Pleiades cluster down to [FORMULA]. Using current-generation theoretical models, we compute the mass of the brown dwarf candidates which is found to range from the hydrogen-burning limit down to about 0.045[FORMULA]. Based on these results, a preliminary estimate of the Pleiades mass function is presented. While the stellar portion of the Pleiades mass function is well approximated by the log-normal IMF of Miller & Scalo (1979), the substellar part of it is found to be slightly higher than predicted by Miller & Scalo's IMF. In a log-log plot, the IMF is found to be still rising in the substellar domain, with a slope consistent with dN/dM [FORMULA] M-0.6 if a power-law functional form is assumed. We estimate a total of about 250 objects below the hydrogen burning mass limit in the Pleiades which nevertheless make up only a few per cent of the mass of the cluster.

Key words: stars: low-mass, brown dwarfs – stars: luminosity function, mass function – Galaxy: open clusters and associations: individual: Pleiades = Melotte 22 – Galaxy: open clusters and associations: general

* Based on observations obtained at the Canada-France-Hawaii Telescope and the KPNO 4m telescope.

Send offprint requests to: J. Bouvier

© European Southern Observatory (ESO) 1998

Online publication: July 20, 1998

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