Anneal Efficacy in HST’s Advanced Camera for Surveys Wide Field Channel and Validation of Reduced Operate Anneal Mode

Since installation aboard the Hubble Space Telescope in 2002, the Advanced Camera for Surveys (ACS) undergoes a monthly annealing process that is effective in reducing dark current in the Wide Field Channel (WFC) pair of CCD detectors. After failing to return to operate mode following two completed anneals in early 2019, ACS suffered back to back safing events. As a result, a new Reduced Operate Anneal (ROA) mode was implemented in October 2019 to avoid future reboot failures. In this poster, we investigate the efficacy of anneals in reducing the global dark current throughout the entire history of ACS, as well as measure the effects of the newly instated ROA mode through an analysis of two different sets of pre and post anneal dark frames. We conclude that ROA mode is similar or more effective in reducing the global dark current and the covering percentage of CCD of hot and warm pixels in the ACS/WFC.