16893

The purpose of this program is to empirically determine the commanding overheads for WFC subarray modes comma both unflashed and post-flashed. The commanding overheads are small periods of time comma beyond the exposure time and any post-flash duration comma over which dark current accrues. Though small comma they impact dark correction and the pixel-based CTE model parameters. Previous work on this topic used hot pixels in a small number of very short comma unflashed subarray darks. The post-flashed subarray overheads were bootstrapped from full-frame overheads. Hot pixels are now known to fade with exposure time comma and their dark rates are most uncertain-variable at short exposure times. We therefore wish to re-determine the empirical commanding overheads by obtaining 32 subarray dark frames with virgul340s darktime comma half of which will be post-flashed to virgul55 e-. We will correct the hot pixels in these frames for their fading rates comma using other data comma to more accurately determine the commanding overheads. We will take 16 subarray dark frames with 337s exposure time and no post-flash comma using the WFC1B-1K. We will also take an identical set of subarray darks with 55e- post-flash. All of the observations should be taken during the same anneal period and preferably within two days in order to avoid the appearance of many unstable hot pixels. The intent is for this CAL program to be scheduled nearly immediately (with the SMS currently being built) to help fill unused internal orbits during HST.s return to science with ACS.