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 H[subscript 2]O and CH[subscript 4] absorption bands, consistent with a T7.5 spectral type, and we see possible indications of NH[subscript 3] 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 [subscript eff] = 650 ± 60 K, log g = 5.2 ± 0.4 cgs, [M/H] ≤ –0.3, and K[subscript zz] = 10[superscript 4] cm[superscript 2] s[superscript –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 over –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.