New Photometric Calibration of the Wide Field Camera 3 Detectors

We present a new photometric calibration of the WFC3-UVIS and WFC3-IR detectors based on observations collected from 2009 to 2020 for four white dwarfs-namely, GRW +70 5824, GD 153 , GD 71 , G191B2B-and a G-type star, P330E. These calibrations include recent updates to the Hubble Space Telescope primary standard white dwarf models and a new reference flux for Vega. Time-dependent inverse sensitivities for the two WFC3-UVIS chips, UVIS1 and UVIS2, were calculated for all 42 full-frame filters after accounting for temporal changes in the observed count rates with respect to a reference epoch in 2009. We also derived new encircled energy values for a few filters and improved sensitivity ratios for the two WFC3-UVIS chips by correcting for sensitivity changes with time. Updated inverse sensitivity values for the 20 WFC3-UVIS quad filters and 15 WFC3-IR filters were derived by using the new models for the primary standards, the new Vega reference flux, and, in the case of the IR detector, new flat fields. However, these values do not account for any sensitivity changes with time. The new calibration provides a photometric internal precision better than 0.5% for the wide-, medium-, and narrowband WFC3-UVIS filters; 5% for the quad filters; and 1% for the WFC3-IR filters. As of 2020 October 15, an updated set of photometric keywords were populated in the WFC3 image headers.