Finding Ultracool Brown Dwarfs With MegaCam On CFHT: Method And First Results

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Delorme, P.
Willott, C. J.
Forveille, T.
Delfosse, X.
Reyle, C.
Bertin, E.
Albert, L.
Artigau, E.
Robin, A. C.
Allard, F.

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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 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. Conclusions. The completed survey will discover similar to 100 T dwarfs and similar to 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.



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Delorme, Philippe, Chris J. Willott, Thierry Forveille, Xavier Delfosse, Céline Reylé, Emmanuel Bertin, Loic Albert et al. >Finding ultracool brown dwarfs with MegaCam on CFHT: method and first results.> Astronomy & Astrophysics, Vol. 484, No. 2 (Jun., 2008): 469-478.