APPLICATION POSSIBILITIES FOR THE HIPPARCOS INTERMEDIATE ASTROMETRIC DATA F. van Leeuwen

Examples of how and when to use the Hipparcos intermediate astrometric data are presented. It is shown how, through the use of the intermediate astrometric data, correlation problems can be properly accounted for. Applications are in general limited to three kinds: calibrations of a common parallax and proper motion for stars in clusters, calibrations of common luminosity properties for stars distributed over the entire sky, and the determination of orbital motion caused by an unseen companion. In the first case, the main advantage is the possibility to eliminate correlations between astrometric parameters and the possibility to incorporate ground-based observations. In the second case, the advantage is in the reduction of degrees of freedom and the homogeneity in which all original observations are incorporated in one solution. In both cases a much improved distinction of faulty measurements is possible. The analysis of possible orbital motions and the detection of unseen companions i..