O.M.Smirnov, O.Yu.Malkov
Inst.Astr., Russian Acad.Sci.
Evaluating the properties of the 1593 individual plates used in forming the Guide Star Catalog (GSC) is an important part of the RGSC (Refined GSC) project currently in progress at the Center for Astronomical Data, Moscow. Many GSC objects appear on more than one plate and thus have several catalog entries, this allows us to perform `multi-plate analysis'' (MPA)--comparing data for the same object from different plates to verify and/or improve it. However, the magnitudes, classifications, and to a lesser extent coordinates given in each entry for an object depend on plate quality and other characteristics as much as they do on the object per se. In effect, each plate presents its individually biased view of the object. Therefore, determining the properties of the plates is crucial for correct MPA. One important plate property that is being determined is the "0-3-0" tendency. The GSC entries originating from some plates tend to misclassify stellar (GSC type 0) and extended (type 3) objects more consistently than those from other plates. This tendency can also depend on the distance from plate center. Other vital plate characteristics are limiting and saturation magnitude, magnitude biasing, and topological incompleteness. We will present algorithms for automatically determining these parameters on a per-plate basis, and for building a complete plate atlas for visual evaluations.