DIVA -: A space-borne fizeau interferometer for global astrometry and photometry

DIVA (Double Interferometer for Visual Astrometry) is a small space mission planned to be launched in 2003. It will perform an astrometric and photometric sky survey unbiased from a specific input catalogue. DIVA will measure the positions, proper motions and parallaxes of all stars down to 15th visual magnitude. After 2 years of observations, the typical accuracy for a star with V = 9 and B-V = 0.9 will be 0.2 milliarcseconds (mas) for the parallaxes, 0.15 mas for the positions and 0.3 mas/y for the proper motions. DIVA will improve the parallaxes of the Hipparcos stars by a factor of 5; the proper motions by a factor of 10 when combined with the Hipparcos results. This will maintain and improve the Hipparcos optical reference system for the foreseeable future. Broad-band photometry will be obtained for all the 35 million objects of the survey. Additionally, multi-channel intermediate-band photometry will be provided by DIVA for the brightest 10 million stars (V less than or equal to 13.5).