Speckle observations with PISCO in Merate: VI. Astrometric measurements of visual binaries in 2006

We present relative astrometric measurements of visual binaries made during the second semester of 2006, with the speckle camera 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 175 new measurements of 169 objects, with angular separations in the range 0″.1–4″.2, and an average accuracy of 0″.01. The mean error on the position angles is 0°.6. Most of the position angles could be determined without the usual 180° ambiguity with the application of triplecorrelation techniques and/or by inspection of the long integration files.We also present the new orbits we have computed for ADS 11479, 11584 and 16538, for which our measurements lead to large residuals and/or for which the revision was justified by the significant number of observations made since the last orbit computation (© 2009 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)