DIVA - An interferometric minisatellite for astrometry and photometry

We propose a small interferometer on a minisatellite, named DIVA (Deutsches Interferometer für Vielkanalphotometrie und Astrometrie), to perform astrometric and photometric observations of at least one million stars. It would exceed the performance of Hipparcos in all important parameters. With a possible launch in 2002 DIVA would provide for all stars brighter than V = 10^m.5 - parallaxes better than 0.8 milliarcseconds (mas) - proper motions better than 2 mas/y - broad-band photometry with a typical accuracy of 0.002 mag - multi-channel intermediate-band photometry with a typical accuracy of 0.01 to 0.02 mag For the 100 000 stars observed by Hipparcos, proper motions with a typical accuracy of 0.1 to 0.2 mas/y and parallaxes of 0.3 to 0.5 mas can be obtained in combination with the Hipparcos results. The scientific potential of this mission and a possible layout of its optical system are described in this paper.