Relative astrometry with Hipparcos: double stars with orbital motion.

Abstract

During the Hipparcos data analysis an algorithm was developed to study orbital motion in double stars and to derive the seven Dommanget parameters in the positive cases. Three approaches were followed: linear motion model, quadratic motion model and orbital model. In the last model the algorithm needs sufficiently good starting values and it has been applied to a set (756) of known orbital doubles. 600 of the obtained solutions have been considered acceptable for further detailed analysis and critical discussion. It turned out that for long period orbits the results are useful just as an estimate of relative positions at the Hipparcos mission time, while for short periods the whole reconstructed orbit can assume interesting physical meaning. The method is described and the results are globally discussed.