0 FLASH level may be too low for this exposure or a short subexposure. See extended explanation in the diagnostic browser FLASH level may be too low for this exposure or a short subexposure. See extended explanation in the diagnostic browser FLASH level may be too low for this exposure or a short subexposure. See extended explanation in the diagnostic browser FLASH level may be too high for this exposure or a long subexposure. See extended explanation in the diagnostic browser FLASH level may be too high for this exposure or a long subexposure. See extended explanation in the diagnostic browser FLASH level may be too high for this exposure or a long subexposure. See extended explanation in the diagnostic browser FLASH level may be too high for this exposure or a long subexposure. See extended explanation in the diagnostic browser Hi Wes, The goal of this 2-orbit external calibration program is to develop some recommendations for Cycle 29 proposers. The proposal deadline will be in early spring, so getting the data sooner would be a real benefit. The target (Omega Cen) comes out of occultation on Dec 16 or so. I have put a formal window between now and January 15, but the sooner the data can be taken after Dec 16, the easier it will be to get the analysis done in time to support the proposers. Let me know if you have any questions! All the best, Jay 1872355815 ----- Attempting Submission 1 (Thu Nov 12 19:26:27 GMT 2020) ----- We are deliberately exploring post-flash levels. 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, however stars are different from warm pixels. Their profiles involve multiple pixels, and the downstream pixels can have a significant shielding effect on the upstream pixels. Although the pixel-based models include this effect in principle, it is hard to evaluate exactly how shielding in the model compares with shielding in the real detectors. Therefore, it is useful to observe actual stars to evaluate the model. In addition, 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, therefore its noise will be amplified by any pixel-based reconstruction process. For faint sources, 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, 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, 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, while also increasing the noise. This program is similar to CAL-14881, except that the target is Omega Cen instead of the bulge and we are finely sampling sky levels between 10e and 30e for UVIS, 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, wider variety of backgrounds. We are also observing ACS in parallel at 4 background levels. This program involves two external orbits. We will place WFC3/UVIS on the center of globular cluster Omega Centauri, and ACS in parallel on a field that is about 6' away. In each orbit, we are able to collect four short and two deep full-frame WFC3/UVIS exposures per orbit, and two short and two deep 2Kx2K subarray ACS observations. There will be no dithering in this program, since the goal is to establish the "true" scene from the 800s deep exposures, then to downscale this true scene to the short exposures with different backgrounds in order to see how the background level affects the distribution/preservation of charge. From the archive, 40s exposures of the scene at the center of Omega Cen have a background of 26e in WFC3/UVIS. This is way too high for our purposes of exploring the background between 10e and 30e. So we will scale down these exposure times to 4s so that we can get a background of 2.6e. We can then add postflash to get it into our desired range. For ACS at a 6' removed field, the natural background should be quite small, so our postflash will define the background. For UVIS we will probe 8 background levels: 10e, 12e, 14e, 16e, 19e, 22e, 25e, and 29e. For ACS we will probe 4 backgrond levels: 10e, 20e, 30e, and 40e. 4s exposures should have ~30,000 stars in each UVIS field in each magnitude bin at the faint end. This will provide us a very clear measurement of how stellar profiles vary with flux and background level. The deep exposures will be 800s, so we will scale them down by a factor of 200, which will provide a very robust "truth" image for evaluating the short exposures. Saturation in the deep exposures should not have a big impact. Jay Anderson pioneered the pixel-based CTE correction for ACS/WFC and WFC3/UVIS. He will do most of the analysis and documentation of these results. Benjamin Kuhn is in charge of the regular empirical CTE monitoring programs. These programs do not have as many stars at the faint end as this program will, but tying the two together will be important. Sylvia Baggett is team lead of the WFC3 branch. She will help us package the results and distribute them to users and potential users via ISRs, white papers, STAN articles, etc. 0 false false RESTRICTED EXT-CLUSTER GLOBULAR CLUSTER This object was generated by the targetselector and retrieved from the SIMBAD database. J2000 1605208744137 /Users/jayander/Desktop/OP-cache/JAY_OMCCTE_16441a-v02.xml The scheduling data was generated by CASM 28.2. CASM was run in Phase II mode. 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