P19	March 1998

¹ Institut d'Astrophysique et de Géophysique - Université de Liège, Avenue de Cointe 5, 4000 Liège, Belgium
² Space Telescope Science Institute, 3700 San Martin Drive, Baltimore, MD 21218, USA

^* Directeur de Recherches FNRS (Belgium)

Abstract

     Based on observed PSFs from the WFPC2 calibration programs, series of PSF subtraction tests have been performed and the resulting photometry analyzed. We find that using a composite observed PSF, constructed from optimally selected PSFs based on location and breathing values, yields single photometric values affected by an RMS dispersion of about 0.01-0.02 mag. While resampling does not appear to have much of an effect on the photometric results, the color of the PSF employed is important.