干旱区生态环境知识资源中心

We use three field L and T dwarfs that were discovered to be wide companions to known stars by the Two Micron All-Sky Survey to derive a preliminary brown dwarf companion frequency. Observed L and T dwarfs indicate that brown dwarfs are not unusually rare as wide (Delta > 1000 AU) systems to F-M0 main-sequence stars (M > 0.5 M., M-v < 9.5), even though they are rare at close separation ( < 3 AU; the "brown dwarf desert"). Stellar companions in these separation ranges are equally frequent, but brown dwarfs are 10 times as frequent for wide than close separations. A brown dwarf wide-companion frequency as low as the 0.5% seen in the brown dwarf desert is ruled out by currently available observations.