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The mass and age of substellar objects are degenerate parameters leaving the evolutionary state of brown dwarfs ambiguous without additional information. Theoretical models are normally used to help distinguish between old, massive brown dwarfs and young, low mass brown dwarfs but these models have yet to be properly calibrated. We have carried out an infrared high-contrast imaging program with the goal of detecting substellar objects as companions to nearby stars to help break degeneracies in inferred physical properties such as mass, age, and composition. Rather than using imaging observations alone, our targets are pre-selected based on the existence of dynamical accelerations informed from years of stellar radial velocity (RV) measurements. In this paper, we present the discovery of a rare benchmark brown dwarf orbiting the nearby ($d=18.69pm0.19$ pc), solar-type (G9V) star HD 4747 ([Fe/H]=$-0.22pm0.04$) with a projected separation of only $rho=11.3pm0.2$ AU ($theta approx$ 0.6). Precise Doppler measurements taken over 18 years reveal the companions orbit and allow us to place strong constraints on its mass using dynamics ($m sin(i) = 55.3pm1.9M_J$). Relative photometry ($Delta K_s=9.05pm0.14$, $M_{K_s}=13.00pm0.14$, $K_s - L = 1.34pm0.46$) indicates that HD 4747 B is most-likely a late-type L-dwarf and, if near the L/T transition, an intriguing source for studying cloud physics, variability, and polarization. We estimate a model-dependent mass of $m=72^{+3}_{-13}M_J$ for an age of $3.3^{+2.3}_{-1.9}$ Gyr based on gyrochronology. Combining astrometric measurements with RV data, we calculate the companion dynamical mass ($m=60.2pm3.3M_J$) and orbit ($e=0.740pm0.002$) directly. As a new mass, age, and metallicity benchmark, HD 4747 B will serve as a laboratory for precision astrophysics to test theoretical models that describe the emergent radiation of brown dwarfs.
The physical properties of faint stellar and substellar objects often rely on indirect, model-dependent estimates. For example, the masses of brown dwarfs are usually inferred using evolutionary models, which are age dependent and have yet to be prop
The physical properties of brown dwarf companions found to orbit nearby, solar-type stars can be benchmarked against independent measures of their mass, age, chemical composition, and other parameters, offering insights into the evolution of substell
Monitoring the long-term radial velocity (RV) and acceleration of nearby stars has proven an effective method for directly detecting binary and substellar companions. Some fraction of nearby RV trend systems are expected to be comprised of compact ob
We present L band (3.8 $mu m$) MMT/Clio high-contrast imaging data for the nearby star GJ 758, which was recently reported by Thalmann et al. (2009) to have one -- possibly two-- faint comoving companions (GJ 758B and ``C, respectively). GJ 758B is d
The nearby Sun-like star HD 19467 shows a subtle radial velocity (RV) acceleration of -1.37+/-0.09 m/s/yr over an 16.9 year time baseline (an RV trend), hinting at the existence of a distant orbiting companion. We have obtained high-contrast adaptive