|WFC3 Instrument Handbook for Cycle 25|
A.1 IntroductionThis appendix contains plots of throughputs and sensitivities for each WFC3 filter. It is organized by detector and filter. For each imaging mode the following are provided:
• Tables of color corrections ABν to go from Johnson V magnitude to AB magnitude for stellar spectra (as a function of effective temperature) and composite populations (as a function of age). The stellar spectra come from the Lejeune et al. (1997, A&AS, 125, 229) grid, and assume a surface gravity of log g = 5 and solar metallicity. The composite populations come from the “instantaneous burst” and “continuous star formation” models of Bruzual & Charlot (1993, ApJ, 405, 539), updated in 1995, assuming a Salpeter IMF spanning 0.1 to 125 solar masses.The plots presented here were derived using on-orbit data that was processed with ground-based flat field reference files. (See WFC3 ISR 2009-30 and WFC3 ISR 2009-31) These flat fields are in error by up to several percent on large spatial scales (see Sections 5.4.3 and 5.7.4.). Monitoring of photometric performance over the first year of operations showed the WFC3/UVIS detector to be stable to rms ~ 0.5% (WFC3 ISR 2010-14) and the WFC3/IR detector to be stable to rms ~ 0.5% to 1.0%, depending on filter (WFC3 ISR 2011-08). Small photometric drifts have been detected in the UVIS channel during continued monitoring from 2009 to mid-2014 (WFC3 ISR 2014-20). There has been a slight increase in throughput in the UV filters (~0.1%/year) and slight decreases in throughput in red and visible filters (0.2%/year and 0.4%/year, respectively). No contamination effects have been detected.We provide photometric transformation coefficients for converting magnitudes from the native WFC3/UVIS passbands to Johnson/Cousins UBVRI passbands in the ABMAG, STMAG, and VEGAMAG systems in WFC3 ISR 2014-16.