Speckle observations with PISCO in Merate - I. Astrometric measurements of visual binaries in 2004

We present relative astrometric measurements of visual binaries made with the Pupil Interferometry Speckle camera and Coronagraph (PISCO) at the 1-m Zeiss telescope of Brera Astronomical Observatory, in Merate. We provide 135 new observations of 103 objects, with angular separations in the range 0.1-4.0 arcsec and with an accuracy better than similar to0.01 arcsec. Our sample is made of orbital couples as well as binaries whose motion is still uncertain. Our purpose is to improve the accuracy of the orbits and constrain the masses of the components. This work already leads to the revision of the orbits of three systems (ADS 5447, 8035 and 8739).