Prospects of Brown Dwarf Detection by Near-Infrared Surveys (DENIS, 2MASS)

Abstract

Forthcoming large-scale near-infrared surveys (DENIS/2MASS) will certainly discover thousands of new very low-mass stars, but it is less clear how many brown dwarfs. Until recently, there were no good examples of these elusive substellar objects. Hence, it was difficult to foresee the number of them that near-IR surveys could detect. Fortunately, the situation has radically changed within the last year, and three bona-fide brown dwarfs have been officially reported so far. We have focused on the properties of the first two brown dwarfs discovered, namely Teide 1 and Gl229B, to estimate the sensitivity of DENIS/2MASS to this new kind of object. The privileged photometric band is J, because it sets the limit for the faintest brown dwarfs that can be detected. We estimate that several hundreds of brown dwarfs will be present in the J-band all-sky surveys. The majority of them will be luminous and young like Teide 1, and a hand-ful will be faint and old like Gl229B. Photometric detection is a necessary, but not at all sufficient condition for indentifying brown dwarfs. An im-portant corollary is that follow-up observations (parallax, proper motion, spectroscopy, lithium) of photometric candidates are indispensable to assess their substellar nature.