ACS-RMulti-Parameter Optimization Constraints

The repaired ACS WFC will undergo a three-week Optimization Campaign during early SMOV with read noise being the primary target for improvements through testing adjustments of a large number of detector control, voltage and timing patterns. A large number of factors, in addition to read noise, contribute to the utility of science data from ACS WFC. In this TIR we enumerate several such factors including Charge Transfer Efficiency (CTE), Full Well Depth (FWD), Linearity, Cross talk, gain stability and bias drift. For each we quantify values that existed when WFC was last used in January 2007 and provide extrapolation that we believe would have existed with a continuously operable instrument to May 2009. For each factor we provide qualitative discussion of how changes would impact science in order to provide a framework for considering changes that may arise during the Optimization Campaign. In many cases, e.g. for CTE, significant deterioration of performance from nominal expectations as a result of changes during the optimization campaign would provide support for adjusting the optimization to lessen this, even at the cost of some increase of read noise.