Hipparcos Astrometric Binaries in the Ninth Catalogue of Spectroscopic Binary Orbits: A Testbench for the Detection of Astrometric Binaries with Gaia

The Ninth Catalogue of Spectroscopic Binary Orbits1 and the Hipparcos Intermediate Astrometric Data (IAD) are used to retrieve astrometric binaries from the Hipparcos data. It is found that basically all (non-SB2) systems with periods larger than about 100 d, and parallaxes larger than 5-10 mas exhibit an astrometric orbital motion which can be extracted from the IAD. The lessons learned from this kind of approach will be very valuable for the design of the Gaia reduction pipeline.