THE DETECTION OF LOW-MASS COMPANIONS IN HYADES CLUSTER SPECTROSCOPIC BINARY STARS

We have observed a large sample of spectroscopic binary stars in the Hyades cluster, using high-resolution infrared spectroscopy to detect low-mass companions. We combine our double-lined infrared measurements with well-constrained orbital parameters from visible light single-lined observations to derive dynamical mass ratios. Using these results, along with photometry and theoretical mass-luminosity relationships, we estimate the masses of the individual components in our binaries. In this paper we present double-lined solutions for 25 binaries in our sample, with mass ratios from similar to 0.1 to 0.8. This corresponds to secondary masses as small as similar to 0.15 M(circle dot). We include here our preliminary detection of the companion to vB 142, with a very small mass ratio of q = 0.06 +/- 0.04; this indicates that the companion may be a brown dwarf. This paper is an initial step in a program to produce distributions of mass ratio and secondary mass for Hyades cluster binaries with a wide range of periods, in order to better understand binary star formation. As such, our emphasis is on measuring these distributions, not on measuring precise orbital parameters for individual binaries.