Speckle observations with PISCO in Merate (Italy): XVI. Astrometric measurements of visual binaries in 2015, and new orbits for DUN 5, ADS 5958, 6276, 7294, 8211, and 13169

We present relative astrometric measurements of visual binaries, made in 2015 with the speckle camera PISCO at the 102-cm Zeiss telescope of Brera Astronomical Observatory, in Merate. Our observing list contains orbital couples as well as binaries whose motion is still uncertain. We obtained 196 new measurements of 173 visual binary stars, with angular separations in the range 0 ′′ .27-11.3 ′′ , and an average accuracy of 0 ′′ .019. The mean error on the position angles is 0 • .6. 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 present new revised orbits for DUN 5, ADS 5958, 6276, 7294, 8211 and 13169, partly derived from PISCO observations. The corresponding estimated values for the masses of those systems are compatible with the spectral types. We also computed new rectilinear elements for ADS 4841 for which the physical connection is doubtful from our (and other recent) observations.