A survey of proper-motion stars. XV. Orbital solutions for 34 double-lined spectroscopic binaries

We present orbital solutions for 34 double-lined spectroscopic binaries found in the Carney-Latham sample of 1464 stars selected for high proper motion. We use TODCOR, a two-dimensional correlation technique, to extract the velocities for the primary and secondary stars and their light ratio. For our single-order echelle spectra, obtained with the Center for Astrophysics Digital Speedometers, we find that we can reach secondaries that are as much as 2 mag fainter than their primaries. The ratio of the primary to secondary velocity residuals from the orbital fit equals approximately the secondary-to-primary light ratio, as would be expected for the photon-limited case. We use our mass and light ratios to evaluate the mass-luminosity relation for metal-poor main-sequence dwarfs in the mass range 0.55-0.8 M_⊙. We assume an L ∝ script M sign^β relation and find that the exponent at around 5200 Å is 7.4 ± 0.6. We find this is in good agreement with the slope of the corresponding theoretical M_V-script M sign 14 Gyr isochrones from the VandenBerg & Bell models for metal-poor stars.