Binary Star Masses from Hipparcoss

The parallaxes from Hipparcos are an important ingredient to derive more accurate masses for known orbital binaries. In order to exploit the parallaxes fully, the orbital elements have to be known to similar precision, and the present work is a rst survey of the orbital systems with parallax errors below about 5 per cent. With methods combining the inter-mediatèTransit Data' (published in the Hipparcos Catalogue) with the existing ground-based data, we have made solutions that improve both the orbital elements and in some cases also the Hipparcos data. In particular, some systems with only a photocentre position or orbit in the Hipparcos Catalogue can now bèresolved' and a magnitude-diierence estimated. In all, we have made provisional re-derivations of some 130 sets of orbital elements, giving in the end some 45 mass-sum values with an estimated relative accuracy better than 15 per cent. For some 15 short-period systems, a pure astrometric mass ratio has been determined , but for main-sequence systems, suuciently accurate mass ratios can be estimated from the observed magnitude-diierences. This gives nally an observed`mass-luminosity relation' in good agreement with stellar evolution theory.