ULAS J141623.94+134836.3: A BLUE T DWARF COMPANION TO A BLUE L DWARF

We confirm the substellar nature of ULAS J141623.94+134836.3 (aka SDSS J1416+1348B), a common proper motion companion to the blue L dwarf SDSS J141624.08+134826.7 identified by Burningham et al. and Scholz. Low-resolution 0.8-2.4 mu m spectroscopy obtained with the Infrared Telescope Facility/SpeX shows strong H(2)O and CH(4) absorption bands, consistent with a T7.5 spectral type, and we see possible indications of NH(3) absorption in the 1.0-1.3 mu m region. More importantly, the spectrum of SDSS J1416+1348B shows a broadened Y-band peak and highly suppressed K-band flux, both indicative of high surface gravity and/or subsolar metallicity. These traits are verified through spectral model fits, from which we derive atmospheric parameters T(eff) = 650 +/- 60 K, log g = 5.2 +/- 0.4 cgs, [M/H] <= -0.3, and K(zz) = 10(4) cm(2) s(-1), the temperature being significantly warmer than that estimated by Burningham et al. These fits also indicate a model-dependent spectroscopic distance of 10.6(-2.8)(+3.0) pc for SDSS J1416+1348B, formally consistent with the 7.9 +/- 1.7 pc astrometric distance for SDSS J1416+1348A from Scholz. The common peculiarities of these two co-spatial, co-moving sources suggest that their unusual blue colors-and those of other blue L and T dwarfs in general-arise from age/gravity or metallicity effects, rather than cloud properties alone.