Measurements of visual binaries with PISCO2 at the Nice 76‐cm refractor in 2011–2012

We present relative astrometric and photometric measurements of visual binaries made in 2011–2012, with PISCO2 installed at the 76‐cm refractor of Côte d'Azur Observatory in Nice (France). Our observing list contains orbital couples as well as binaries whose motion is still uncertain. Three different techniques have been used for obtaining those measurements: Lucky imaging, speckle interferometry, and the direct vector autocorrelation method. From our observations of 3,136 multiple stars, we obtained 3,568 new measurements with angular separations in the range of 0 ″ .1–10 ″ and an average accuracy of 0 ″ .016. The mean error on the position angles is 1°.7. Most of the position angles were determined without the usual 180° ambiguity with the application of the direct vector autocorrelation technique and/or by inspection of the Lucky images or the long integration files. We managed to routinely monitor faint systems ( m V  ≈ 9–11) with large magnitude difference (up to Δ m V  ≈ 5). We have thus been able to measure many systems containing red dwarf stars that had been poorly monitored since their discovery. We also measured the magnitude difference of the two components of 326 binaries with an estimated error of 0.2 mag. Except for a few objects that have been discussed, our measurements are in a good agreement with the ephemerides computed with published orbital elements, even for the binaries closer than the diffraction limit. Thanks to good seeing images and with the use of high‐contrast numerical filters, we have also been able to obtain 196 measurements with an angular separation smaller than the diffraction limit of our instrumentation, and consistent with those obtained with larger telescopes. We also obtained new measurements of the 15th magnitude multiple system CON37, and discovered a faint new double star in its vicinity. Finally, we report 47 measurements of 28 new binaries found during our observations.