ACS CCD Gains, Full Well Depths, and Linearity up to and Beyond Saturation

The CCDs on ACS may both be operated at multiple gain settings. Analysis of calibration and science data is used to establish corrections to the supported HRC GAIN=4 and WFC GAIN=2 values; relative to the default gains decreased values of e-/DN of 1.27% and 0.78% respectively are indicated. Maps of the full well depth at which saturation sets in for both HRC and WFC are provided, both cameras show spatial variations in excess of 10%. When operated with gains that fully sample the full well depth, the CCDs remain perfectly (<0.1% relative count levels) linear to well beyond saturation with simple summation over pixels that have been bled into as a result of over-saturation. Linearity at levels from marginal detection in single exposures, to multiple levels up to saturation, and at multiple levels beyond saturation are presented showing excellent results.