Visual binary orbits and masses post Hipparcos

The parallaxes from Hipparcos are an important ingredient to derive more accurate masses for known orbital binaries, but in order to exploit the parallaxes fully, the orbital elements have to be known to similar precision. The present work gives improved orbital elements for some 205 systems by combining the Hipparcos astrometry with existing ground-based observations. The new solutions avoid the linearity constraints and omissions in the Hipparcos Catalog by using the intermediate Transit Data which can be combined with ground-based observations in arbitarily complex orbital models. The new orbital elements and parallaxes give new mass-sum Values together with realistic total error-estimates. To get individual masses at least for main-sequence systems, the mass-ratios have been generally estimated from theoretical isochrones and observed magnitude-differences. For some 25 short-period systems, however, true astrometric mass-ratios have been determined through the observed orbital curvature in the 3-year Hipparcos observation interval. The final result is an observed 'mass-luminosity relation' which falls close to theoretical expectation, but with 'outliers' due to undetected multiplicity or to composition- and age-effects in the nonuniform near-star sample.