Volume 522, November 2010
|Number of page(s)||15|
|Section||Galactic structure, stellar clusters and populations|
|Published online||09 November 2010|
The ultracool-field dwarf luminosity-function and space density from the Canada-France Brown Dwarf Survey⋆,⋆⋆
Observatoire de Besançon, Université de Franche-Comté, Institut Utinam, UMR
, BP 1615,
2 School of Physics and Astronomy, University of St Andrews, North Haugh, St Andrews KY16 9SS, UK
3 Herzberg Institute of Astrophysics, National Research Council, 5071 West Saanich Rd, Victoria, BC V9E 2E7, Canada
4 Canada-France-Hawaii Telescope Corporation, 65-1238 Mamalahoa Highway, Kamuela, HI96743, USA
5 Laboratoire d’Astrophysique de Grenoble, Université J. Fourier, CNRS, UMR5571, Grenoble, France
6 Département de physique and Observatoire du Mont Mégantic, Université de Montréal, C.P. 6128, Succursale Centre-Ville, Montréal, QC H3C 3J7, Canada
7 McDonald Observatory, University of Texas at Austin, 1 University Station C1402, Austin, TX 78712-0259, USA
Accepted: 7 August 2010
Context. Thanks to recent and ongoing large scale surveys, hundreds of brown dwarfs have been discovered in the last decade. The Canada-France Brown Dwarf Survey is a wide-field survey for cool brown dwarfs conducted with the MegaCam camera on the Canada-France-Hawaii Telescope.
Aims. Our objectives are to find ultracool brown dwarfs and to constrain the field brown-dwarf luminosity function and the mass function from a large and homogeneous sample of L and T dwarfs.
Methods. We identify candidates in CFHT/MegaCam i′ and z′ images and follow them up with pointed near infrared (NIR) imaging on several telescopes. Halfway through our survey we found ~ 50 T dwarfs and ~ 170 L or ultra cool M dwarfs drawn from a larger sample of 1400 candidates with typical ultracool dwarfs i′ − z′ colours, found in 780 square degrees.
Results. We have currently completed the NIR follow-up on a large part of the survey for all candidates from mid-L dwarfs down to the latest T dwarfs known with utracool dwarfs’ colours. This allows us to draw on a complete and well defined sample of 102 ultracool dwarfs to investigate the luminosity function and space density of field dwarfs.
Conclusions. We found the density of late L5 to T0 dwarfs to be objects pc-3, the density of T0.5 to T5.5 dwarfs to be objects pc-3, and the density of T6 to T8 dwarfs to be objects pc-3. We found that these results agree better with a flat substellar mass function. Three latest dwarfs at the boundary between T and Y dwarfs give the high density objects pc-3. Although the uncertainties are very large this suggests that many brown dwarfs should be found in this late spectral type range, as expected from the cooling of brown dwarfs, whatever their mass, down to very low temperature.
Key words: stars: low-mass / brown dwarfs / stars: luminosity function, mass function / Galaxy: stellar content
Based on observations obtained with MegaPrime/MegaCam, a joint project of CFHT and CEA/DAPNIA, at the Canada-France-Hawaii Telescope (CFHT), which is operated by the National Research Council (NRC) of Canada, the Institut National des Sciences de l’Univers of the Centre National de la Recherche Scientifique (CNRS) of France, and the University of Hawaii. This work is based in part on data products produced at TERAPIX and the Canadian Astronomy Data Centre as part of the Canada-France-Hawaii Telescope Legacy Survey, a collaborative project of NRC and CNRS. Based on observations made with the ESO New Technology Telescope at the La Silla Observatory. Based on observations obtained at the Gemini Observatory, which is operated by the Association of Universities for Research in Astronomy, Inc., under a cooperative agreement with the NSF on behalf of the Gemini partnership: the National Science Foundation (United States), the Science and Technology Facilities Council (United Kingdom), the National Research Council (Canada), CONICYT (Chile), the Australian Research Council (Australia), CNPq (Brazil) and CONICET (Argentina). Based on observations with the Kitt Peak National Observatory, National Optical Astronomy Observatory, which is operated by the Association of Universities for Research in Astronomy, Inc. (AURA) under cooperative agreement with the National Science Foundation. Based on observations made with the Nordic Optical Telescope, operated on the island of La Palma jointly by Denmark, Finland, Iceland, Norway, and Sweden, in the Spanish Observatorio del Roque de los Muchachos of the Instituto de Astrofisica de Canarias. Based on observations made at The McDonald Observatory of the University of Texas at Austin.
Tables 3, 5 and 8 are only available in electronic form at http://www.aanda.org
© ESO, 2010
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