Hipparcos astrometric binaries

The Input Catalogue of some 100000 stars that is presently prepared for observation by the astrometric satellite HIPPARCOS, will contain many double and multiple systems. Because of the Hipparcos observation technique, these systems have to be divided in a few particular categories that are described and discussed. Each of them leads to specific considerations concerning the contribution of the Hipparcos observations. The category of very close pairs to which Hipparcos will certainly add many systems newly discovered during the mission, is compared to that of the few astrometric pairs that have been discovered by groundbased techniques.Hipparcos appears finally as a very important tool in double star astronomy research and especially in the field of very close systems.Communication presented at the International Conference on Astrometric Binaries, held on 13–15 June, 1984, at the Remeis-Sternwarte Bamberg, Germany, to commemorate the 200th anniversary of the birth of Friedrich Wilhelm Bessel (1784–1846).