Cross Matching Sources In the Hubble Legacy Archive (HLA)

Lubow, Steve

We have begun a project to cross identify sources observed in different HST exposures. We first determine the set of overlapping exposures which would have objects in common. We apply the object source lists for the exposures currently available in the HLA. For each set of overlapping exposures, we determine trimmed source list of possible cross matches using a Bayesian method developed by Budavari and Szalay (2008). We apply a novel algorithm for shifting the exposures into common alignment. We then update the positions of the objects and repeat the computation of the trimmed source list and exposure shifts iteratively until no further improvement is obtained. In preliminary tests, we have been able to obtain mean relative astrometric shifts between exposures of order of a few milliarcseconds.

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