The temporal optical behavior of the Hubble Space Telescope: the impact on science observations

Though the Hubble Space Telescope (HST) has proven to be a stable platform for astronomical observations when compared with ground-based imaging, it features its own characteristic optical variations that have required post-observation processing to support the full range of science investigations that should be possible with HST. While the overall system focus has been monitored and adjusted throughout the life of the Observatory, the recent installation of the Advanced Camera for Surveys and its High Resolution Camera has allowed us to use phase retrieval techniques to accurately measure changes in coma and astigmatism as well. The aim of this current work is to relate these measurements of wave front error back to characterizations more common to science data analysis (e.g. FWHM, and ellipticity). We show how variations in these quantities over the timescales observed may impact the photometric and astrometric precision required of many current HST programs, as well as the characterization of barely-resolved objects. We discuss how improved characterization and modeling of the point spread function (PSF ) variations may help HST observers achieve the full science capabilities of the Observatory.

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