Finding ultracool brown dwarfs with MegaCam on CFHT: method and first results

Philippe Delorme (1) , Chris W, C.J. Willott (2) , Thierry Forveille (1, 3, 4) , Xavier Delfosse (1, 4) , Céline Reylé (5) , Emmanuel Bertin (6) , Loic Albert (3) , Etienne Artigau (7) , Annie C. Robin (5) , France Allard (8) , Rene Doyon (9) , Gary J. Hill (10)

1 LAOG - Laboratoire d'Astrophysique de Grenoble
2 Department of Physics [Ottawa]
3 CFHT - Canada-France-Hawaii Telescope Corporation
4 OSUG - Observatoire des Sciences de l'Univers de Grenoble
5 LAOB - Laboratoire d'astrophysique de l'observatoire de Besançon (UMR 6091)
6 IAP - Institut d'Astrophysique de Paris
7 Gemini Observatory [Southern Operations Center]
8 CRAL - Centre de Recherche Astrophysique de Lyon
9 Departement de physique and Observatoire du Mont Megantic
10 McDonald Observatory

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. 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. We have so far analysed over 350 square degrees and found 770 brown dwarf candidates brighter than z'{AB}=22.5. 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. 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.

Domaines: Cosmologie et astrophysique extra-galactique [astro-ph.CO]

Philippe Delorme, Chris W, C.J. Willott, Thierry Forveille, Xavier Delfosse, Céline Reylé, et al.. Finding ultracool brown dwarfs with MegaCam on CFHT: method and first results. 2008. ⟨hal-00398510v1⟩