Speckle observations of binary stars with the WIYN telescope. II. Relative astrometry measures during 1998-2000

Five hundred twelve relative astrometry measures are presented for 253 double stars, including 53 double stars discovered by Hipparcos. In 15 cases, relative astrometry is reported for the first time for newly confirmed pairs. In addition, 20 high-quality nondetections of companions are reported for stars suspected of being nonsingle by Hipparcos. Observations were taken using a fast-readout CCD camera system at the WIYN 3.5 m telescope at Kitt Peak, Arizona. In comparing these measures with ephemeris predictions for binary stars with very well known orbits, we find that the measurement precision is better than 3 mas in separation and 1degrees in position angle per individual observation. Measurement precision and detection capabilities are fully discussed, and confirmed orbital motion is reported in four cases of the Hipparcos double star discoveries.