Dynamical Masses for the Hyades Binary System vB 120

Abstract

We report spectroscopic observations of vB 120 (HD 30712), a 5.7 yr astrometric–spectroscopic binary system in the Hyades cluster. We combine our radial velocities with others from the literature, and with existing speckle interferometry measurements, to derive an improved 3D orbit for the system. We infer component masses of M 1 = 1.065 ± 0.018 M ☉ and M 2 = 1.008 ± 0.016 M ☉, and an orbital parallax of 21.86 ± 0.15 mas, which we show to be more accurate than the parallax from Gaia DR3. This is the ninth binary or multiple system in the Hyades with dynamical mass determinations, and one of the examples with the highest precision. An analysis of its spectral energy distribution yields the absolute radii of the stars, R 1 = 0.968 ± 0.012 R ☉ and R 2 = 0.878 ± 0.013 R ☉, and effective temperatures of 5656 ± 56 K and 5489 ± 60 K for the primary and secondary, respectively. A comparison of these properties with the predictions of current stellar evolution models for the known age and metallicity of the cluster shows only minor differences.