Volume 484, Number 2, June III 2008
|Page(s)||469 - 478|
|Section||Stellar structure and evolution|
|Published online||16 April 2008|
Finding ultracool brown dwarfs with MegaCam on CFHT: method and first results *
Laboratoire d'Astrophysique de Grenoble,Université J. Fourier, CNRS, UMR5571, Grenoble, France e-mail: Philippe.Delorme@obs.ujf-grenoble.fr
2 University of Ottawa, Physics Department, 150 Louis Pasteur, MacDonald Hall, Ottawa, ON K1N 6N5, Canada
3 Observatoire de Besançon, Institut Utinam, UMR CNRS 6213, BP 1615, 25010 Besançon Cedex, France
4 Institut d'Astrophysique de Paris-CNRS, 98bis Boulevard Arago, 75014, Paris, France
5 Canada-France-Hawaii Telescope Corporation, 65-1238 Mamalahoa Highway, Kamuela, HI96743, USA
6 Gemini Observatory Southern Operations Center c/o AURA, Casilla 603 La Serena, Chile
7 C.R.A.L. (UMR 5574 CNRS), École Normale Supérieure, 69364 Lyon Cedex 07, France
8 Département de physique and Observatoire du Mont Mégantic, Université de Montréal, CP 6128, Succursale Centre-Ville, Montréal, QC H3C 3J7, Canada
9 McDonald Observatory, University of Texas at Austin, 1 University Station C1402, Austin, TX 78712-0259, USA
Accepted: 2 April 2008
Aims. We present the first results of a wide field survey for cool brown dwarfs with the MegaCam camera on the CFHT telescope, the Canada-France Brown Dwarf Survey, hereafter CFBDS. Our objectives are to find ultracool brown dwarfs and to constrain the field-brown dwarf mass function thanks to a larger sample of L and T dwarfs.
Methods. We identify candidates in CFHT/MegaCam i' and z' images using optimised psf-fitting within Source Extractor, and follow them up with pointed near-infrared imaging on several telescopes.
Results. We have so far analysed over 350 square degrees and found 770 brown dwarf candidates brighter than . We currently have J-band photometry for 220 of these candidates, which confirms 37% as potential L or T dwarfs. Some are among the reddest and farthest brown dwarfs currently known, including an independent identification of the recently published ULAS J003402.77-005206.7 and the discovery of a second brown dwarf later than T8, CFBDS J005910.83-011401.3. Infrared spectra of three T dwarf candidates confirm their nature, and validate the selection process.
Conclusions. The completed survey will discover ~100 T dwarfs and ~500 L dwarfs or M dwarfs later than M8, approximately doubling the number of currently known brown dwarfs. The resulting sample will have a very well-defined selection function, and will therefore produce a very clean luminosity function.
Key words: stars: low-mass, brown dwarfs / techniques: spectroscopic / techniques: photometric / methods: data analysis / surveys
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 under programme ID 76.C-0540(A), 77.C-0594, 77.A-0707, 78.A-0651, 78.C-0629 and 79.A-0663. 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. This paper includes data taken at The McDonald Observatory of The University of Texas at Austin.
© ESO, 2008
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