Speckle observations with PISCO in Merate - IX. Astrometric measurements of visual binaries in 2008

Abstract

We present relative astrometric measurements of visual binaries, made in 2008 with the Pupil Interferometry Speckle camera and Coronagraph (PISCO) at the 102 cm Zeiss telescope of Brera Astronomical Observatory, in Merate. Our sample contains orbital couples as well as binaries whose motion is still uncertain. We obtained 240 new measurements of 237 objects with angular separations in the range 0.15–4.6 arcsec, and an average accuracy of 0.014 arcsec. The mean error on the position angles is . Most of the position angles were determined without the usual 180° ambiguity with the application of triple-correlation techniques and/or by inspection of the long integration files. We have found a new component in ADS 11074. This component was not fully resolved in our previous observations of 2006, but it was clearly separated with the observations presented here. We also present the new revised orbits we have computed for ADS 11468, 13850 and 16057, for which our measurements lead to large residuals with the last published orbits. For ADS 13850, we propose to extend the quadrant correction that was previously used by the other authors to the first measurements made before 1930. In this way, we obtain an orbit with a longer period which leads to a much more plausible value for the total mass of the system.