EDP Sciences
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Volume 434, Number 3, May II 2005
Page(s) 939 - 948
Section Galactic structure, stellar clusters and populations
DOI http://dx.doi.org/10.1051/0004-6361:20042164

A&A 434, 939-948 (2005)
DOI: 10.1051/0004-6361:20042164

A deep, wide-field search for substellar members in NGC 2264

T. R. Kendall1, J. Bouvier1, E. Moraux2, D. J. James1, 3 and F. Ménard1

1  Laboratoire d'Astrophysique, Observatoire de Grenoble, Université Joseph Fourier, 38041 Grenoble Cedex 09, France
    e-mail: [tkendall;jbouvier]@obs.ujf-grenoble.fr
2  Institute of Astronomy, University of Cambridge, Madingley Road, Cambridge CB3 0HA, UK
    e-mail: moraux@ast.cam.ac.uk
3  Department of Physics and Astronomy, Vanderbilt University, 1807 Station B, Nashville, TN 37235, USA

(Received 12 October 2004 / Accepted 16 January 2005)

We report the first results of our ongoing campaign to discover the first brown dwarfs (BD) in NGC 2264, a young (3 Myr), populous star forming region for which our optical studies have revealed a very high density of potential candidates - 236 in <1 deg2 - from the substellar limit down to at least ~20  $M_{\rm Jup}$ for zero reddening. Candidate BD were first selected using wide field (I,z) band imaging with CFH12K, by reference to current theoretical isochrones. Subsequently, 79 (33%) of the I,z sample were found to have near-infrared 2MASS photometry ( $JHK_{\rm s}\pm0.3$ mag or better), yielding dereddened magnitudes and allowing further investigation by comparison with the location of NextGen and DUSTY isochrones in colour-colour and colour-magnitude diagrams involving various combinations of I, J, H and $K_{\rm s}$. We discuss the status and potential substellarity of a number of relatively unreddened ( $A_{\rm v}\la5$) likely low-mass members in our sample, but in spite of the depth of our observations in I,z, we are as yet unable to unambiguously identify substellar candidates using only 2MASS data. Nevertheless, there are excellent arguments for considering two faint (observed $I\sim18.4$ and 21.2) objects as cluster candidates with masses respectively at or rather below the hydrogen burning limit. More current candidates could be proven to be cluster members with masses around 0.1 $M_{\odot}$ via gravity-sensitive spectroscopy, and deeper near-infrared imaging will surely reveal a hitherto unknown population of young brown dwarfs in this region, accessible to the next generation of deep near-infrared surveys.

Key words: stars: low-mass, brown dwarfs -- infrared: stars -- surveys -- Galaxy: open clusters and associations: individual: NGC 2264

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