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

The PDS/Monet measuring engine at NOAO was used to obtain photometry o f nearly 10000 stars on the NGS/POSS and 2000 stars on the ESO/SRC Sur vey glass plates, These measurements have been used to show that globa l transformation functions exist that allow calibration of stellar pho tometry from any blue or red plate to equivalent Johnson B and Cousins R photoelectric magnitudes. We have characterized the four transforma tion functions appropriate for the POSS O and E and ESO/SRC J and R pl ates, and found that within the measurement uncertainties they vary fr om plate to plate only by photometric zero-point offsets. A method is described to correct for the zero-point shifts and to obtain calibrate d 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 calibrati on procedure makes it possible to obtain rapid photometry of very larg e numbers of stellar sources, and is available to general users of the PDS at the National Observatory.