HST Temporal Optical Behavior: Models and Measurements with ACS

While HST provides a stable stellar image relative to ground-based observatories, it features its own characteristic changes in the PSF it delivers to the Science Instruments (Lallo et al. 2005). HST focus has been monitored and adjusted throughout the life of the observatory. More recently, the resolution and off-axis location of ACS/HRC has allowed us to accurately measure changes in coma and astigmatism as well. The aim of this current work is to relate the accurate and reliable phase retrieval measurements of wavefront error back to characterizations more common to science data analysis (e.g. encircled energy, FWHM, ellipticity). We encourage the further examination of these effects on HST science observations.