17262( 2) - 15-Nov-2022 20:16:00 - [ 1] HUBBLE SPACE TELESCOPE OBSERVING PROGRAM 17262 Version: 2 Check-in Time: 15-Nov-2022 20:16:00 STScI Edit Number: 0 Title WFC3/UVIS Faint-Source CTE Characterization ------------------------------------------------------------------------------------ Type Cycle CAL/WFC3 30 ------------------------------------------------------------------------------------ Investigators Contact? PI: Dr. Jay Anderson Space Telescope Science Institute Y CoI: Benjamin Kuhn Space Telescope Science Institute N CoI: Dr. Sylvia M. Baggett Space Telescope Science Institute N ------------------------------------------------------------------------------------ Abstract This program is a follow-on to CAL-16441 (PI-Anderson), which examined how faint sources near the background are impacted by CTE (charge-transfer efficiency) losses. See WFC3/ISR 2021-09 for a description of CAL-16441's findings. Many WFC3/UVIS programs involve taking multiple long exposures of fields in order to find extremely faint sources that cannot be detected reliably in single exposures. It is unclear how well the pixel-based CTE-correction algorithm is able to correct for CTE losses when the sources are very close to the background. We need to assess this directly so that we can help observes plan and interpret their observations. The previous program --- CAL-16441 --- explored backgrounds from 0e to 30e, spanning the levels that users get when they post-flash low-background images (or when they neglect to use a proper post-flash). CTE continues to improve beyond 30e, and observations with wide-band filters often get natural backgrounds higher than 30e, so it is useful to extend the CAL-16441 analysis to backgrounds from 30e all the way up to 100e. In particular, users often decide whether to take 3 exposures per orbit or 2 exposures per orbit (or even one exposure per orbit) based on CTE considerations. CTE improves in two ways with fewer longer exposures: (1) the source flux per exposure is larger, and (2) the natural background per exposure is larger. The downside is that cosmic rays impact more pixels in longer exposures. This 1-orbit external program will help users better weigh their options. We will take backgrounds of 20e, 35e, 50e, 70e, and 100e. The 20e background is so that we can have a more direct tie-in at the current epoch to the "recommended" level. We will take two deep exposures to provide the "truth" against which the short 1s exposures are compared. ------------------------------------------------------------------------------------ Observations Description ------------------------ We will take five short 1-s exposures with post-flashed backgrounds of 20e, 35e, 50e, 70e, and 100e, and two deep 350-s exposures of the same field with no dither. The deep exposures can be combined to show us the true astronomical scene present in the short exposures. The survival of flux in the variously post-flashed short exposures will tell us about how CTE impacts faint sources 17262( 2) - 15-Nov-2022 20:16:00 - [ 2] near background levels from 20e up to 100e. The medium post-flash gives about 85e per second (from FIg 16 of WFC3/ISR 2013-12, Biretta & Baggett) . So: 25e = 0.3s * 85 e/s 34e = 0.4s * 85 e/s 51e = 0.6s * 85 e/s 76e = 0.9s * 85 e/s 105e = 1.2s * 85 e/s ------------------------------------------------------------------------------------ 17262( 2) - 15-Nov-2022 20:16:00 - [ 3] TARGET LIST Fixed Targets ------------------------------------------------------------------------------------------------------------------------------------ Tar| Target | Target | Target |Coord | Radial | Flux data No | Name | Description | Position |Eqnx | Vel. | ------------------------------------------------------------------------------------------------------------------------------------ 1 OMEGACEN EXT-CLUSTER, GLOBULAR RA=13H26M47.2400S, J2000 V = -10.26 CLUSTER DEC=-47D28'46.45" Reference Frame: ICRS ------------------------------------------------------------------------------------------------------------------------------------ 17262( 2) - 15-Nov-2022 20:16:00 - [ 4] Visit: 01 (OMEGA CEN) Visit Requirements: On Hold Comments: Additional Comments: Take five short 1-s exposures with various postflash and two long 350-s exposures. The long exposures can be scaled down by x350 (6.3 mags), such that a star near saturation with 70000 counts in the deep exposure will have 200 counts in the central pixel in the short 1s images. And marginally detectable stars with 5e in their central pixels in the short exposures will have 1750 counts in their central pixels in the deep exposures. We use "medium" flash for all these exposures for consistency. The medium flash gets about 85e/s. Thus Exposures ------------------------------------------------------------------------------------------------------------------------------------ Exp | Target | Instr | Oper. | Aper |Spectral|Central| Optional |Num| Time | Special Num | Name | Config | Mode | or FOV |Element |Waveln.| Parameters |Exp| (Total) | Requirements ------------------------------------------------------------------------------------------------------------------------------------ 1 OMEGACEN WFC3/UVI ACCUM UVIS-CENT F606W FLASHCUR=MEDIUM, FLASHEXP=0.3 1 1 S (1 S) S ER ------------------------------------------------------------------------------------------------------------------------------------ 2 OMEGACEN WFC3/UVI ACCUM UVIS-CENT F606W FLASHCUR=MEDIUM, FLASHEXP=0.4 1 1 S (1 S) S ER ------------------------------------------------------------------------------------------------------------------------------------ 3 OMEGACEN WFC3/UVI ACCUM UVIS-CENT F606W FLASHCUR=MEDIUM, FLASHEXP=0.6 1 1 S (1 S) S ER ------------------------------------------------------------------------------------------------------------------------------------ 4 OMEGACEN WFC3/UVI ACCUM UVIS-CENT F606W FLASHCUR=MEDIUM, FLASHEXP=0.9 1 1 S (1 S) S ER ------------------------------------------------------------------------------------------------------------------------------------ 5 OMEGACEN WFC3/UVI ACCUM UVIS-CENT F606W FLASHCUR=MEDIUM, FLASHEXP=1.2 1 1 S (1 S) S ER ------------------------------------------------------------------------------------------------------------------------------------ 6 OMEGACEN WFC3/UVI ACCUM UVIS-CENT F606W 1 350 S (350 S ER S) ------------------------------------------------------------------------------------------------------------------------------------ 7 OMEGACEN WFC3/UVI ACCUM UVIS-CENT F606W 1 350 S (350 S ER S) ------------------------------------------------------------------------------------------------------------------------------------ Sub Exposures ------------------------------------------------------------------------------------------------------------------------------------ Target | Exp |Instr | Oper. | Aper |Spectral|Cent.|Primary |Secondary |Iteration |CR-SPLIT |Orbit |Duration Name | Num |Config | Mode | or FOV |Element |Wave.|Pattern Pos |Pattern Pos |Num |Num |Number | ------------------------------------------------------------------------------------------------------------------------------------ OMEGACEN 1 WFC3/UVI ACCUM UVIS-CEN F606W none none none none 1 N/A S TER OMEGACEN 2 WFC3/UVI ACCUM UVIS-CEN F606W none none none none 1 N/A S TER OMEGACEN 3 WFC3/UVI ACCUM UVIS-CEN F606W none none none none 1 N/A S TER OMEGACEN 4 WFC3/UVI ACCUM UVIS-CEN F606W none none none none 1 N/A S TER 17262( 2) - 15-Nov-2022 20:16:00 - [ 5] Sub Exposures ------------------------------------------------------------------------------------------------------------------------------------ Target | Exp |Instr | Oper. | Aper |Spectral|Cent.|Primary |Secondary |Iteration |CR-SPLIT |Orbit |Duration Name | Num |Config | Mode | or FOV |Element |Wave.|Pattern Pos |Pattern Pos |Num |Num |Number | ------------------------------------------------------------------------------------------------------------------------------------ OMEGACEN 5 WFC3/UVI ACCUM UVIS-CEN F606W none none none none 1 N/A S TER OMEGACEN 6 WFC3/UVI ACCUM UVIS-CEN F606W none none none none 1 N/A S TER OMEGACEN 7 WFC3/UVI ACCUM UVIS-CEN F606W none none none none 1 N/A S TER 17262( 2) - 15-Nov-2022 20:16:00 - [ 6] Summary Form for Proposal 17262 Item Used in this proposal ------------------------------------------------------------------------------------------------------------------------------------ Apertures UVIS-CENTER ------------------------------------------------------------------------------------------------------------------------------------ Configurations WFC3/UVIS ------------------------------------------------------------------------------------------------------------------------------------ Opmodes ACCUM ------------------------------------------------------------------------------------------------------------------------------------ Optional Parameters FLASHCUR=MEDIUM, FLASHEXP=0.3, FLASHEXP=0.4, FLASHEXP=0.6, FLASHEXP=0.9, FLASHEXP=1.2 ------------------------------------------------------------------------------------------------------------------------------------ Spectral Elements F606W ------------------------------------------------------------------------------------------------------------------------------------ Target Names OMEGACEN ------------------------------------------------------------------------------------------------------------------------------------