Eighteen Years of the Hubble Space Telescope’s Advanced Camera for Surveys: Calibration Update

The Advanced Camera for Surveys (ACS) has been a workhorse Hubble Space Telescope (HST) imager for over eighteen years, subsequent to its Servicing Mission 3B installation in 2002. The once defunct ACS Wide Field Channel (WFC) has now been operating over twice as long (>11yrs) since its Servicing Mission 4 (SM4) repair than it had originally operated prior to its 2007 failure. Despite the accumulating radiation damage to the WFC CCDs during their long stay in low Earth orbit, ACS continues to be heavily exploited by the HST community as both a prime and a parallel detector. We present results from long-term monitoring of WFC dark current and readout noise, results from new studies of detector performance for both WFC and the ACS Solar Blind Channel (SBC), and updated ACS software tools for the user community. Highlights include: 1) an updated measurement of, and correction formula for, point-source photometry affected by degraded WFC charge transfer efficiency (CTE); 2) robust photometry of badly saturated stars newly enabled by enhanced WFC saturation-trail flagging; and 3) long-term monitoring of the SBC multi-anode microchannel array (MAMA) detector sensitivity changes in each of its broadband FUV filters.