Nineteen 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 nineteen 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 (>12yrs) 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 new studies of detector performance for both WFC and the ACS Solar Blind Channel (SBC), including long-term monitoring of WFC and SBC dark current and WFC readout noise. We also advertise updated ACS documentation and software tools for the user community. Highlights include: 1) predictive non-linear modeling of WFC hot-pixel dark current for improved dark subtraction; 2) linkage of SBC dark current rate versus operating temperature, and operating temperature versus time-of-use; 3) validation of the time-evolving WFC geometric distortion solution, exploiting new precise astrometry of the ACS calibration field (globular cluster 47 Tucanae) provided by the Gaia Early Data Release 3; and 4) advertising a new opportunity for high-precision optical/near-IR spectropolarimetry at high spatial resolution (~0.1 arcsec) using paired ACS WFC grism and polarizer filters.