PHOTOMETRIC CALIBRATION OF NGS POSS AND ESO SRC PLATES USING THE NOAO PDS MEASURING ENGINE .1. STELLAR PHOTOMETRY

The PDS/Monet measuring engine at NOAO was used to obtain photometry of nearly 10000 stars on the NGS/POSS and 2000 stars on the ESO/SRC Survey glass plates, These measurements have been used to show that global transformation functions exist that allow calibration of stellar photometry from any blue or red plate to equivalent Johnson B and Cousins R photoelectric magnitudes. We have characterized the four transformation functions appropriate for the POSS O and E and ESO/SRC J and R plates, and found that within the measurement uncertainties they vary from plate to plate only by photometric zero-point offsets. A method is described to correct for the zero-point shifts and to obtain calibrated B and R photometry of stellar sources to an average accuracy of 0.3-0.4 mag within the range 8 less-than-or-equal-to R less-than-or-equal-to 19.5 for red plates in both surveys, 9 less-than-or-equal-to B less-than-or-equal-to 20.5 on POSS blue plates, and 10 less-than-or-equal-to B less-than-or-equal-to 20.5 on ESO/SRC blue plates. This calibration procedure makes it possible to obtain rapid photometry of very large numbers of stellar sources, and is available to general users of the PDS at the National Observatory.