Calibrations for GSC II

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Last Updated Jan 2001

Copyright 2001 The Association of Universities for Research in Astronomy, Inc. All Rights Reserved.

Astrometry:
The astrometry of the GSC II is based on a two step process. First all the plates are individually reduced using a quadratic polynomial solution. Second, systematics that are common to a set of plates were removed. The reference catalogs used were with ACT and the Tycho Catalog II.

Photometry:
The photometric calibration is based on a Chebyshev polynomial fit to sequence stars from the GSPC 2 and the Tycho Catalog for the bright end.

Classification:
Objects in the GSC II are classified as stars or nonstars. Nonstars may be either galaxies, or blended objects with overlapping images on the Schmidt source plate material. Classification was performed using a set of oblique decision trees generated using the OC1 algorithm. Thirty classification features were used, and the features were ranked before use in order to compensate for plate-to-plate variations. Final classification was determined by a vote of classifications from overlapping plates.