ULAS J141623.94+134836.3: A blue t dwarf companion to a blue l dwarf

Abstract

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 μm spectroscopy obtained with the Infrared Telescope Facility/SpeX shows strong H2O and CH4 absorption bands, consistent with a T7.5 spectral type, and we see possible indications of NH3 absorption in the 1.0-1.3 μm 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 Kzz = 104cm2s-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 +3.0-2.8 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. © 2010. The American Astronomical Society. All rights reserved.