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Results are presented that compare the classical plate model method for finding stellar positions with that of the subplate algorithm. This latter procedure has been applied to Schmidt plates where it has shown a distinct improvement in positional accuracy for these type of plates.
Although there is no body of evidence that astrographic plate reductions are dominated by systematic effects, as a trial here we apply the subplate method to 64 plates from the Southern Polar Zone of the Yale Photographic Catalogue. These are 11 degree plates taken on the Yale Southern Astrograph in 1955 and originally reduced by Philip Lu using a 20 constant classical single plate model. Hence, owing to their large size, if systematic effects are present, we should be able to easily determine them (and then eliminate them with the subplate re-reduction).
To objectively determine which procedure is superior, we compare the resultant positions to an independent high quality external reference catalogue, the International Reference Catalogue. This allows us to check the difference in positional precision, the existence of systematics, and the validity of the internal error estimates for both methods.
This research has been supported under the Long Term Visitors Program of the Space Telescope Science Institute and a NASA grant to make subplate reduction code portable.
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