17013

The gain is the conversion factor from electronic analog digital units (ADUs) to electrons and so is a fundamental parameter needed to characterize the WFC3 IR detector. In order to ensure that the true value in each quadrant does not deviate significantly from the nominal gain setting of 2.5 e--ADU within the WFC3-IR data reduction pipeline comma the gain must be monitored each cycle. We propose an observing program for the IR channel of WFC3 that will measure the gain in each of the four quadrants of the detector with a series of flat field pairs taken no more than a week apart comma performed first in winter 2021-22 and again in summer 2022. For each quadrant of each ramp pair comma the measured mean signal is plotted against the variance. The gain is the inverse of the slope of the best fit line. This proposal is an identical continuation of Cycle 29.s program 16577. Ramp pairs are taken twice a year comma providing two separate calculations of gain each cycle.