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2010 CFHT Users Meeting
November 16-18, 2010
ASIAA Auditorium, Taipei, Taiwan

Oral Presentation

Brown Dwarfs from the CFBDS: Their Space Density and Ultracool Atmospheres

Author(s): Delorme P., Albert L., Reyle C., Artigau E., Delfosse X., Forveille T.

Presenter: Philippe Delorme (Laboratoire d’Astrophysique de Grenoble)

A vast majority of the hundreds of brown dwarfs identified since the first discoveries in 1995 come from large scale surveys such as 2MASS, SDSS and DENIS. The Canada-France Brown Dwarfs Survey (CFBDS), conducted at the Canada-France-Hawaii Telescope (CFHT), and ULAS, at UKIRT, are second generation surveys exploring a smaller fraction of the sky but at an increased depth. The CFBDS is based on deep multi-colour MegaCam optical imaging obtained in part in the course of the Legacy Survey but mostly by PI programs. Candidate
brown dwarfs and quasars are initially identified on the MegaCam optical images as objects which have very red colours (high i'-z' colours). Near-infrared J-band imaging is subsequently performed to separate high redshift quasars and brown dwarfs. Beside isolating tens of high redshift quasars so important in probing the reionization of the Universe, the J-band photometry very
efficiently rejected the remaining observational artifacts, such as M-stars scattered in the colour-colour diagram into the brown dwarf/quasar selection region by large noise excursions. Together with the CFBDSIR, its near-infrared extension targeted at the coolest brown dwarfs, CFBDS has identified a sample of over 80 T-type and hundreds L-type brown dwarfs which puts constraints on their space density and mass function. We also discovered several of the
coolest substellar objects known and analysed their spectra to probe atmosphere physics in the 500K range and contrain atmosphere models.

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