WFPC2 Photometry from Subtraction of Observed PSFs

Based on observed PSFs from the WFPC2 calibration programs, a 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 of ~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.