The Orbits and Dynamical Masses of the Castor System

Abstract Castor is a system of six stars in which the two brighter objects, A and B, revolve around each other every ∼450 yr are both short-period spectroscopic binaries. They attended by more distant C, also binary. Here we report interferometric observations with Center for High Angular Resolution Astronomy (CHARA) array that spatially resolve companions B first time. We complement these new radial velocity measurements spanning 30 yr, Hipparcos intermediate data, existing astrometric visual AB pair obtained over past three centuries. perform joint orbital solution to solve simultaneously three-dimensional orbits as well orbit. find they far from being coplanar: orbit nearly at right angles (92°) relative wide orbit, inclined about 59° compared AB. determine dynamical masses four precision better than 1%. radii primary subsystems their angular diameters measured CHARA array, use them together stellar evolution models infer an age 290 Myr. The knowledge enables us measure slow motion C well, may assist future studies this remarkable sextuple system.