2011ApJ...740..108L

We have identified CFBDSIR J1458+1013 as a 0".11 (2.6 AU) physical binary using Keck laser guide star adaptive optics imaging and have measured a distance of 23.1±2.4 pc to the system based on near-IR parallax data from the Canada-France-Hawaii Telescope. The integrated-light near-IR spectrum indicates a spectral type of T9.5, and model atmospheres suggest a slightly higher temperature and surface gravity than the T10 dwarf UGPS J0722-05. Thus, CFBDSIR J1458+1013AB is the coolest brown dwarf binary found to date. Its secondary component has an absolute H-band magnitude that is 1.9±0.3 mag fainter than UGPS J0722-05, giving an inferred spectral type of >T10. The secondary's bolometric luminosity of ∼2x10^–7 L_☉ makes it the least luminous known brown dwarf by a factor of 4-5. By comparing to evolutionary models and T9-T10 objects, we estimate a temperature of 370±40 K and a mass of 6-15 M_Jup for CFBDSIR J1458+1013B. At such extremes, atmospheric models predict the onset of novel photospheric processes, namely, the appearance of water clouds and the removal of strong alkali lines, but their impact on the emergent spectrum is highly uncertain. Our photometry shows that strong CH₄absorption persists in the H band, the J - K color is bluer than the latest known T dwarfs but not as blue as predicted by current models, and the J - H color delineates a possible inflection in the blueward trend for the latest T dwarfs. Given its low luminosity, atypical colors, and cold temperature, CFBDSIR J1458+1013B is a promising candidate for the hypothesized Y spectral class. However, regardless of its ultimate classification, CFBDSIR J1458+1013AB provides a new benchmark for measuring the properties of brown dwarfs and gas-giant planets, testing substellar models, and constraining the low-mass limit for star formation.