Last Updated Jan 2001

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

The photometric calibration of the GSC II is based on the Guide Star Photometric Catalog II and the Tycho catalog to tie down the bright end. The photographic magnitudes given in the GSC II are in the natural systems of the photographic plates from which they where obtained (see GSC plate material for bandpass information).

The transformations from the photometric reference system to the GSC II bandpasses were determined by synthetic photometry using SYNPHOT package in IRAF. Using these color transformations the reference stars magnitudes were converted to those of the GSC bandpasses. Using a general Chebyshev polynominal a least squares fit between the measured integrated density and the reference stars magnitudes in the GSC bandpass was performed. The resulting coefficients were then used to convert all measured integrated densities to magnitudes.