WFPC2 PSF Subtractions

Subtraction of scaled PSFs from direct CCD images of quasars (or stars) offers not only the possibility of detecting the presence of host or foreground galaxies (or companions like brown dwarfs or planets) but also provides a means of deriving accurate photometry of the primary objects. A series of PSF subtraction tests have been performed, using observed PSFs from the WFPC2 PSF Library as well as TinyTim PSFs; preliminary results indicate that appropriate synthetic TinyTim PSFs perform as well as observed PSFs. Specifically, using an optimally selected observed PSF, near the target on the chip ( < 10arcsec ), close in focus (within 1-2 microns), similar in spectral type, and with good S/N, yielded single photometric values with an RMS of ~ 0.01-0.02 mag. Using a carefully constructed synthetic PSF, close in focus and jitter to the target image, and as close as possible to the center of the target, resulted in photometric results with an RMS similar to that achieved with the observed PSF (0.01-0.02 mag).