Astrometry Of Double Stars With Hipparcos

After the processing of 30 months of the observations carried out by HIPPARCOS it is possible to provide reliable statistics on the number of double and multiple stars to be detected at the mission completion and on the quality of the astrometric and photometric results on these objects. About 21 000 stars have been recognized as non-single, including 12 000 already known as double and multiple before the mission and 9000 discovered by Hipparcos. Also, a subset of 16 000 stars among the 21 000 have been successfully solved for their relative coordinates (position angle and separation) with an accuracy in the range of 3 to 30 mas, including 6000 new double stars. We outline in this paper the principle of the processing specific to double, and present the first nearly real size analysis of the results for both the relative and absolute astrometry.