Speckle observations with PISCO in Merate - V. Astrometric measurements of visual binaries in 2006

International audienceWe present relative astrometric measurements of visual binaries made during the first semester of 2006, with the Pupil Interferometry Speckle camera and COronagraph at the 102-cm Zeiss telescope of the Brera Astronomical Observatory, in Merate. Our sample contains orbital couples as well as binaries whose motion is still uncertain. We obtained 217 new measurements of 194 objects, with angular separations in the range 0.1-4.2arcsec, and an average accuracy of 0.01arcsec. The mean error on the position angles is 0.5°. About half of those angles could be determined without the usual 180° ambiguity by the application of triple-correlation techniques. We also present a revised orbit for ADS 277 for which the previously published orbit resulted in a large residual from our measurements

The High Angular Resolution Multiplicity of Massive Stars

We present the results of a speckle interferometric survey of Galactic massive stars that complements and expands upon a similar survey made over a decade ago. The speckle observations were made with the KPNO and CTIO 4 m telescopes and USNO speckle camera, and they are sensitive to the detection of binaries in the angular separation regime between 0.03" and 5" with relatively bright companions (Delta V < 3). We report on the discovery of companions to 14 OB stars. In total we resolved companions of 41 of 385 O-stars (11%), 4 of 37 Wolf-Rayet stars (11%), and 89 of 139 B-stars (64%; an enriched visual binary sample that we selected for future orbital determinations). We made a statistical analysis of the binary frequency among the subsample that are listed in the Galactic O Star Catalog by compiling published data on other visual companions detected through adaptive optics studies and/or noted in the Washington Double Star Catalog and by collecting published information on radial velocities and spectroscopic binaries. We find that the binary frequency is much higher among O-stars in clusters and associations compared to the numbers for field and runaway O-stars, consistent with predictions for the ejection processes for runaway stars. We present a first orbit for the O-star Delta Orionis, a linear solution of the close, apparently optical, companion of the O-star Iota Orionis, and an improved orbit of the Be star Delta Scorpii. Finally, we list astrometric data for another 249 resolved and 221 unresolved targets that are lower mass stars that we observed for various other science programs.Comment: 76 pages, 6 figures, 11 table