Orbits and dynamical masses for the active Hyades multiple system HD 284163

We report near-infrared long-baseline interferometric observations of the Hyades multiple system HD 284163, made with the Center for High Angular Resolution Astronomy array, as well as almost 43 yr of high-resolution spectroscopic monitoring at the Center for Astrophysics. Both types of observations resolve the 2.39 d inner binary, and also an outer companion in a 43.1 yr orbit. Our observations, combined with others from the literature, allow us to solve for the 3D inner and outer orbits, which are found to be at nearly right angles to each other. We determine the dynamical masses of the three stars (good to better than 1.4 per cent for the inner pair), as well as the orbital parallax. The secondary component (0.5245 +/- 0.0047 M-circle dot) is now the lowest mass star with a dynamical mass measurement in the cluster. A comparison of these measurements with current stellar evolution models for the age and metallicity of the Hyades shows good agreement. All three stars display significant levels of chromospheric activity, consistent with the classification of HD 284163 as an RS CVn object. We present evidence that a more distant fourth star is physically associated, making this a hierarchical quadruple system.