2014ApJ...781...29C

The nearby Sun-like star HD 19467 shows a subtle radial velocity (RV) acceleration of -1.37±0.09 m/s/yr over a 16.9 yr time baseline (an RV trend), hinting at the existence of a distant orbiting companion. We have obtained high-contrast images of the star using NIRC2 at Keck Observatory and report the direct detection of the body that causes the acceleration. The companion, HD 19467 B, is ΔK_s= 12.57±0.09 mag fainter than its parent star (contrast ratio of 9.4x10^–6), has blue colors J - K_s= -0.36±0.14 (J - H = -0.29±0.15), and is separated by ρ = 1.''653±0.''004 (51.1±1.0 AU). Follow-up astrometric measurements obtained over a 1.1 yr time baseline demonstrate physical association through common parallactic and proper motion. We calculate a firm lower-limit of m ≥ 51.9_–4.3^+3.6M_J for the companion mass from orbital dynamics using a combination of Doppler observations and imaging. We estimate a model-dependent mass of m = 56.7_–7.2^+4.6M_Jup from a gyrochronological age of 4.3_–1.2^+1.0 Gyr. Isochronal analysis suggests a much older age of 9±1 Gyr, which corresponds to a mass of m = 67.4_–1.5+0.9^M_J. HD 19467 B's measured colors and absolute magnitude are consistent with a late T dwarf [~T5-T7]. We may infer a low metallicity of [Fe/H] =-0.15±0.04 for the companion from its G3V parent star. HD 19467 B is the first directly imaged benchmark T dwarf found orbiting a Sun-like star with a measured RV acceleration.