WFC3 UVIS Full Well Depths, and Linearity Near and Beyond Saturation

of the full well depth at which saturation sets in are provided for the two UVIS CCDs on WFC3. The full well depths show about 10% variation over each CCD ranging from 63-71K on UVIS1 and 67-72K on UVIS2. The standard gain of �1.6 e-/DN results in saturation safely being on the CCD rather than in the ADC, and linearity for photometry holds to levels better than 1% generally for UVIS2 to well beyond saturation simply from summation over pixels that have been bled into as a result of over-saturation. For UVIS1 the simple approach to saturated point source photometry shows deviations from linearity up to �15% for oversaturations exceeding 20, but the deviations are easily calibrated enabling linearity to be retained to near 1% even for stars over-saturated by 7 magnitudes.