EDP Sciences
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Volume 400, Number 3, March IV 2003
Page(s) 891 - 902
Section Stellar clusters and associations
DOI http://dx.doi.org/10.1051/0004-6361:20021903

A&A 400, 891-902 (2003)
DOI: 10.1051/0004-6361:20021903

Brown dwarfs in the Pleiades cluster: Clues to the substellar mass function

E. Moraux1, J. Bouvier1, J. R. Stauffer2 and J.-C. Cuillandre3, 4

1  Laboratoire d'Astrophysique, Observatoire de Grenoble, BP 53, 38041 Grenoble Cedex 9, France
2  SIRTF Science Center, California Institute of Technology, Pasadena, CA 91125, USA
3  Canada-France-Hawaii Telescope Corp., Kamuela, HI 96743, USA
4  Observatoire de Paris, 61 Av. de l'Observatoire, 75014 Paris, France

(Received 4 November 2002 / Accepted 19 December 2002 )

We present the results of a 6.4 square degrees imaging survey of the Pleiades cluster in the I and Z-bands. The survey extends up to 3 degrees from the cluster center and is $90\%$ complete down to $I\simeq 22$. It covers a mass range from 0.03  $M_{\odot}$ to 0.48  $M_{\odot}$ and yields 40 brown dwarf candidates (BDCs) of which 29 are new. The spatial distribution of BDCs is fitted by a King profile in order to estimate the cluster substellar core radius. The Pleiades mass function is then derived accross the stellar-substellar boundary and we find that, between $0.03~M_{\odot}$ and $0.48~M_{\odot}$, it is well represented by a single power-law, ${\rm d}N/{\rm d}M\propto M^{-\alpha}$, with an index $\alpha=0.60\pm 0.11$. Over a larger mass domain, however, from 0.03  $M_{\odot}$ to 10  $M_{\odot}$, the mass function is better fitted by a log-normal function. We estimate that brown dwarfs represent about 25% of the cluster population which nevertheless makes up less than 1.5% of the cluster mass. The early dynamical evolution of the cluster appears to have had little effect on its present mass distribution at an age of 120 Myr. Comparison between the Pleiades mass function and the Galactic field mass function suggests that apparent differences may be mostly due to unresolved binary systems.

Key words: stars: low-mass, brown dwarfs -- stars: luminosity function, mass function -- open clusters and associations: individual: Pleiades

Offprint request: E. Moraux, Estelle.Moraux@obs.ujf-grenoble.fr

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