  The star HD 28363 in the Hyades cluster has been known for over a century as
a visual binary with a period of 40 yr. The secondary is, in turn, a
single-lined spectroscopic binary with a 21-day period. Here we report
extensive spectroscopic monitoring of this hierarchical triple system that
reveals the spectral lines of the third star for the first time. Combined with
astrometric information, this makes it possible to determine the dynamical
masses of all three stars. Only six other binaries in the Hyades have had their
individual component masses determined dynamically. We infer the properties of
the system by combining our radial velocity measurements with visual
observations, lunar occultation measurements, and with proper motions from the
Hipparcos and Gaia missions that provide a constraint on the astrometric
acceleration. We derive a mass of 1.341 +/- 0.026/0.024 M(Sun) for the visual
primary, and 1.210 +/- 0.021 M(Sun) and 0.781 +/- 0.014 M(Sun) for the other
two stars. These measurements along with those for the other six systems
establish an empirical mass-luminosity relation in the Hyades that is in broad
agreement with current models of stellar evolution for the known age and
chemical composition of the cluster.
