Double Stars in the Tycho-2 Catalogue

Abstract

The Tycho-2 Catalogue provides astrometric and photometric information for 2.5 million stars. Within the Tycho-2 Catalogue, while there is no separate listing of double-star parameters, there is a wealth of double-star data. For all measured double-star systems, each component has its own entry in Tycho-2 (this corresponds to the Hipparcos ii double-entry systems ˇˇ), and the classical double-star parameters of separation, position angle, and magnitude diUerence can be calculated for these systems. Most double stars in the Tycho-2 Catalogue are identi—ed by a code indicating a double, failed double, or photo- centric solution. Stars —agged in this manner include 6251 known double stars and 1234 new double-star systems (designated in the Washington Double Star Catalog (WDS) with a ii TDS ˇˇ discovery code). Also, 4726 systems solved via Tycho-2 ii single-star treatment ˇˇ not only matched one component of a WDS pair but also had a nearby star that closely approximated the position and magnitude of the other WDS component. Finally, 1133 WDS systems were seen as single in Tycho-2 whose historical double- star parameters would indicate that Tycho-2 should have measured them. The observational statistics of these various classes of objects are presented together with catalog statistics for those with single-star solutions. A quantitative assessment of Tycho-2 double-star measures is provided via a comparison of Tycho-2 O(C residuals to known orbits. Finally, a subset of systems measured by Tycho-2 have been veri—ed via speckle interferometry using the 82 inch (2 m) telescope of McDonald Observatory. These results are presented here.