16441

The calibration programs (such as CAL-16440) that attempt to pin-down the parameters of the CTE model involve a study of warm pixels. This is approprate for evaluating the pixel-based model comma however stars are different from warm pixels. Their profiles involve multiple pixels comma and the downstream pixels can have a significant shielding effect on the upstream pixels. Although the pixel-based models include this effect in principle comma it is hard to evaluate exactly how shielding in the model compares with shielding in the real detectors. Therefore comma it is useful to observe actual stars to evaluate the model. In addition comma one complication of the model involves the readnoise. The pixel-based CTE correction is a necessarily deconvolution process. The readnoise was added after the CTE-blurring took place comma therefore its noise will be amplified by any pixel-based reconstruction process. For faint sources comma it may sometimes be preferable to forego the pixel-based reconstruction (which can amplify readnoise and diminish the significance of the sources) and analyze the _flt images directly comma doing the CTE correction as part of the analysis. The observations in this program will allow users to construct photometric and astrometric corrections for the impact of CTE on faint sources on various backgrounds. Finally comma this program will provide advice to users about how much post-flash to add to maximize the signal-to-noise of their sources. A higher background will preserve more signal comma while also increasing the noise. This program is similar to CAL-14881 comma except that the target is Omega Cen instead of the bulge and we are finely sampling sky levels between 10e and 30e for UVIS comma so that users can dial in the background level that optimizes the signal to noise of their program. The previous program sampled a less useful comma wider variety of backgrounds. We are also observing ACS in parallel at 4 background levels.