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Quantifying Gaia Star Problems for Asteroidal Occultation Predictions

JOA 2021, Vol. 11, No. 3, Page 24

Author(s): David W. Dunham, Steve Preston, Dave Herald, Ted Blank, Roger Venable, Salvador Aguirre, John Moore, Paolo Tanga

Abstract: The title for this paper might rather be, “Beware of High RUWE and Duplicated Source Flag”, since that is the main lesson learned from the occultations that we describe. All three stars have high RUWE (Renormalized Unit Weight Error), a measure of the quality of the astrometric solution for the Gaia positional information of the star. Also, of concern is the “Duplicated Source Flag” that may (but not always) mean that the star’s astrometric information might be degraded by unresolved close duplicity of the star. Fortunately, in each of these cases, we were able to deploy enough stations so that at least a few had occultations, showing where the actual occultation path was, and thus, giving a measure of the actual error in the Gaia astrometric information for the star. One of the stars was a close double; the prediction for it turned out to be more accurate than expected. In another case, the asteroid was (99942) Apophis, opening a new age in near-Earth asteroid precision astrometry.