System of astrometric databases of Pulkovo observatory. ... Pulkovo database of observations of visual double stars . ... The 3rd database contains relative positions of selected double and multiple stars, and stars with possible invisible satellites. The database requires catalog of relative positions of visual double stars, based on photographic observations performed since 1960 on Pulkovo 26-inch refractor, and similar catalog based on CCD observations, obtained since 1995. ...