ABSOLUTE QUADRANT DETERMINATIONS FROM SPECKLE OBSERVATIONS OF BINARY STARS

Reduction of speckle data obtained for binary stars is typically carried out using power spectrum or, equivalently, autocorrelation methods. An especially powerful algorithm from which accurate differential astrometry can be obtained is the vector-autocorrelation technique. While such methods are highly suited to extracting astrometric information from very large volumes of speckle data in near real time, they inherently introduce a 180-degrees ambiguity in the position angle measurement. We here briefly describe why this can be a problem in determining the orbital motions in binaries, present a new algorithm which maintains most of the simplicity of vector autocorrelation while removing the quadrant ambiguity, and provide results of new absolute quadrant determinations for 66 binary star systems first resolved by the long-term GSU/CHARA speckle program carried out at the National Optical Astronomy Observatories. Finally, we use this new algorithm to eliminate the period ambiguity in the orbit of the close visual binary ADS 9744.