7.11 IR Photometry Errors

The estimated errors for the inverse sensitivity of the WFC3 IR channel computed from observations of the white dwarf standards plus a G-type star are ~2% (statistical) 2-3% absolute (systematic, uncertainties in the models used as absolute standards). The signal to noise ratio, per observation, for the standard stars is such that the formal Poisson error is ~0.2% for the wide band filters. For users who need precise photometry, a complete error analysis would include Poisson noise of the science target as well as the additional sources of photometric error of flat fields, spatial repeatability (~1% peak to peak), temporal repeatability (1% peak to peak), readnoise, uncertainty in the encircled energy (~ 0.5% at the infinite aperture - Hartig personal communication), uncertainty in the gain (Section 7.2), and processing errors (sky subtraction, dark subtraction, correction for persistence). We do not yet understand why the photometric repeatability for the IR detector is so poor, this is under active investigation at the current time.