Astrometric Standard Fields for CCD Observations of Double Stars

The number of known double stars is steadily increasing, thanks to ground-based and space observations. Therefore the ratio of known double to single stars has to be revised upwards continuously. With the Hipparcos parallaxes it will be possible to get stellar statistics for precisely defined volumes of space. This will lead to strong constraints on all astrophysical calibrations of masses, spectral types and luminosities in the solar neighbourhood. A European network of laboratories was created in August 1990 in order to remedy the lack of photometric data for close visual double stars. This network intends to study all aspects of formation and evolution of double and multiple star systems. The immediate goal of the group is to provide the scientific community with a compilation of known photometric data on a large selection of close visual double stars and to significantly enlarge this information by new observations with modern devices. A photometric database of stellar systems is being compiled from most widely used photometric systems in collaboration with the ‘Centre de Donnees Stellaires’ of Strasbourg.