Kelu-1 : A Free-floating Brown Dwarf in the Solar Neighborhood

Abstract

We present the discovery of a field brown dwarf, Kelu-1. The object has a peculiar optical spectrum that, in spite of its extremely red color, shows no sign of the TiO and VO absorption bands typical of cool, low-mass stars. The optical spectrum does show the Li i l6708 absorption line and Ha in emission. The infrared spectrum of Kelu-1 has strong H 2 O absorption and also shows the effect of pressure-induced H 2 opacity. Kelu-1 was discovered through its large proper motion of 0Љ .35 yr Ϫ1 , with position angle . A distance of ∼10 pc is ⅙ v ϭ 265 estimated astrometrically for the object, which implies absolute magnitudes of and . Comparison M ∼ 22 M ∼ 12 V K of the observed energy distribution of Kelu-1 to synthetic spectra generated by atmosphere models of Allard et al., and structural and evolutionary models of Chabrier & Baraffe, implies that the object has T ϭ 1900 ‫ע‬ eff K and a mass below 0.075 . 100 M/M ,