17693( 4) - 17-Apr-2025 15:47:32 - [ 1] HUBBLE SPACE TELESCOPE OBSERVING PROGRAM 17693 Version: 4 Check-in Time: 17-Apr-2025 15:47:32 STScI Edit Number: 1 Title WFC3 Astrometric Scale Monitoring ------------------------------------------------------------------------------------ Type Cycle CAL/WFC3 32 ------------------------------------------------------------------------------------ Investigators Contact? PI: Ms. Catherine A Martlin Space Telescope Science Institute Y CoI: Anne O'Connor Space Telescope Science Institute Y CoI: Varun Bajaj Space Telescope Science Institute Y CoI: Dr. Mitchell Revalski Space Telescope Science Institute Y ------------------------------------------------------------------------------------ Abstract The standard astrometric catalog in the field of globular cluster Omega Cen has been used to examine the geometric distortion of WFC3 UVIS and IR as function of wavelength in multi-cycle calibration programs over last 11 years of WFC3 on HST board. All observations from these programs have been reduced and provided the multi-wavelength geometric distortion in UVIS and IR detector. The derived geometric distortion coefficients implemented in the IDCTAB format are used in the HST pipe-line to correct for a ~7% distortion in WFC3/UVIS and IR images down to <1%. Additional to multi-wavelength WFC3 geometric distortion, all observations of Omega Cen taken through F606W and F160W UVIS and IR filters, respectively, during the last 11 years (all together 12 epochs) were used to look for time dependency of UVIS and IR geometric distortion and the effect of the scale change due to the thermal breathing. The results of the stability WFC3 geometric distortion published in WFC3-ISR-2015-02 (Kozhurina-Platais & Anderson, 2015), WFC3-ISR-2019-09 (Martlin, Kozhurina-Platais), have show that the UVIS geometric distortion is stable over 10 years on-orbit within 0.05 pixels or 2 mas in UVIS. The results of WFC3/IR published in WFC3-ISR-09-19 (M. McKay, Kozhurina-Platais, et al) have show that the IR geometric distortion is stable over 10 years on orbits within 0.1 pixel or 2 mas. The same observations were used to examine the WFC3/UVIS and IR photometric changes with time (WFC3-ISR-2020-05, Kozhurina-Platais, Bagget). The purpose of this calibration proposal is to continue the monitor of the stability of the WFC3 geometric distortion over time. The observations of Omega Cen through the UVIS F606W filter and the F160W IR filter will be used to derive the skew and scale terms of the geometric distortion and look for any secular changes over time. In addition, several UVIS and IR filters have been appended for the purposes of generating new PSF models for the community. ------------------------------------------------------------------------------------ Observations Description ------------------------ The observation of Omega Cen through F606W and F160W is used as a standard filter in UVIS and IR, respectively. They are observed with the same pointing but with different roll-angle of the OTA at a single epoch between Jan -April 2026 at an orient of ~290 degrees. 17693( 4) - 17-Apr-2025 15:47:32 - [ 2] The 3 exposures in UVIS have steps of roll-angles -1.5, 0, +1.5 degrees requiring 3 orbits. The same 3 exposures in IR with the steps of roll-angles -1.5, 0, +1.5 degrees also require 3 orbits. To maintain accurate pointing control, 2-guide star acquisitions are used. If suitable guide stars can be found, the same pair of guide stars are used for all exposures. This cycle, additional filters are added for UVIS and IR for the purposes of building additional PSF models, based on usage statistics in GO science programs. ---Calibration Goals--- The geometric distortion of WFC3 in 13 UVIS and 8 IR filters were calibrated using the standard astrometric catalog of Omega Cen (Anderson & van der Marel, 2010). An update set of updated distortions were obtained for 20 UVIS filters using the same standard astrometric catalog of Omega Cen (Kozhurina-Platais, WFC3-ISR-2014-12; Martlin et al. WFC3-ISR-2018-11). The goal of this proposal is to monitor the geometric distortion of both the UVIS and IR detectors. The skew parameter in the ACS/WFC case, is changing with time in the level of 40 mas over 15 years on board of HST. The skew parameter is the non-perpendicularity of coordinate axes and is the major parameter in the geometric distortion model. ------------------------------------------------------------------------------------ 17693( 4) - 17-Apr-2025 15:47:32 - [ 3] TARGET LIST Fixed Targets ------------------------------------------------------------------------------------------------------------------------------------ Tar| Target | Target | Target |Coord | Radial | Flux data No | Name | Description | Position |Eqnx | Vel. | ------------------------------------------------------------------------------------------------------------------------------------ 1 OMEGACEN CALIBRATION, RA=13H26M46.2800S +/- 0.1", J2000 V = 16.8 +/- 0.1 ASTROMETRIC, SPATIAL DEC=-47D28'44.60" +/- 0.1" DISTORTION TEST Reference Frame: ICRS Comments: This is the same target (and coordinates) as used in CAL/WFC3 11911, UVIS L-Flats and Geometric Distortion and in other multi-cycles calibration proposals ------------------------------------------------------------------------------------------------------------------------------------ 17693( 4) - 17-Apr-2025 15:47:32 - [ 4] Visit: 01 (Visit 01 F606W) Visit Requirements: ORIENT 284D TO 284 D; BETWEEN 01-JAN-2026:00:00:00 AND 31-MAR-2026:00:00:00 On Hold Comments: Additional Comments: 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 F606W FLASH=12 1 60.0 S (60 S S) ------------------------------------------------------------------------------------------------------------------------------------ 2 OMEGACEN WFC3/UVI ACCUM UVIS F555W FLASH=14 1 350 S (350 S S) ------------------------------------------------------------------------------------------------------------------------------------ 3 OMEGACEN WFC3/UVI ACCUM UVIS F475W FLASH=14 1 350 S (350 S S) ------------------------------------------------------------------------------------------------------------------------------------ 4 OMEGACEN WFC3/UVI ACCUM UVIS F225W FLASH=21 1 350 S (350 S S) ------------------------------------------------------------------------------------------------------------------------------------ 5 OMEGACEN WFC3/UVI ACCUM UVIS F625W FLASH=14 1 350 S (350 S S) ------------------------------------------------------------------------------------------------------------------------------------ 6 OMEGACEN WFC3/UVI ACCUM UVIS F775W FLASH=14 1 350 S (350 S 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 F606W none none none none 1 N/A S OMEGACEN 2 WFC3/UVI ACCUM UVIS F555W none none none none 1 N/A S OMEGACEN 3 WFC3/UVI ACCUM UVIS F475W none none none none 1 N/A S OMEGACEN 4 WFC3/UVI ACCUM UVIS F225W none none none none 1 N/A S OMEGACEN 5 WFC3/UVI ACCUM UVIS F625W none none none none 1 N/A S OMEGACEN 6 WFC3/UVI ACCUM UVIS F775W none none none none 1 N/A S 17693( 4) - 17-Apr-2025 15:47:32 - [ 5] Visit: 02 (Visit 02 F606W) Visit Requirements: ORIENT 285.5D TO 285.5 D; BETWEEN 01-JAN-2026:00:00:00 AND 31-MAR-2026:00:00:00 On Hold Comments: Additional Comments: 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 F606W FLASH=12 1 60.0 S (60 S S) ------------------------------------------------------------------------------------------------------------------------------------ 2 OMEGACEN WFC3/UVI ACCUM UVIS F390W FLASH=14 1 350 S (350 S S) ------------------------------------------------------------------------------------------------------------------------------------ 3 OMEGACEN WFC3/UVI ACCUM UVIS F218W FLASH=21 1 350 S (350 S S) ------------------------------------------------------------------------------------------------------------------------------------ 4 OMEGACEN WFC3/UVI ACCUM UVIS F547M FLASH=14 1 350 S (350 S S) ------------------------------------------------------------------------------------------------------------------------------------ 5 OMEGACEN WFC3/UVI ACCUM UVIS F845M FLASH=14 1 350 S (350 S S) ------------------------------------------------------------------------------------------------------------------------------------ 6 OMEGACEN WFC3/UVI ACCUM UVIS F763M FLASH=14 1 350 S (350 S 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 F606W none none none none 1 N/A S OMEGACEN 2 WFC3/UVI ACCUM UVIS F390W none none none none 1 N/A S OMEGACEN 3 WFC3/UVI ACCUM UVIS F218W none none none none 1 N/A S OMEGACEN 4 WFC3/UVI ACCUM UVIS F547M none none none none 1 N/A S OMEGACEN 5 WFC3/UVI ACCUM UVIS F845M none none none none 1 N/A S OMEGACEN 6 WFC3/UVI ACCUM UVIS F763M none none none none 1 N/A S 17693( 4) - 17-Apr-2025 15:47:32 - [ 6] Visit: 03 (Visit 03 F606W) Visit Requirements: ORIENT 287D TO 287 D; BETWEEN 01-JAN-2026:00:00:00 AND 30-MAR-2026:00:00:00 On Hold Comments: Additional Comments: 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 F606W FLASH=12 1 60.0 S (60 S S) ------------------------------------------------------------------------------------------------------------------------------------ 2 OMEGACEN WFC3/UVI ACCUM UVIS F621M FLASH=14 1 350 S (350 S S) ------------------------------------------------------------------------------------------------------------------------------------ 3 OMEGACEN WFC3/UVI ACCUM UVIS F656N FLASH=21 1 350 S (350 S S) ------------------------------------------------------------------------------------------------------------------------------------ 4 OMEGACEN WFC3/UVI ACCUM UVIS F502N FLASH=21 1 350 S (350 S S) ------------------------------------------------------------------------------------------------------------------------------------ 5 OMEGACEN WFC3/UVI ACCUM UVIS F657N FLASH=21 1 350 S (350 S S) ------------------------------------------------------------------------------------------------------------------------------------ 6 OMEGACEN WFC3/UVI ACCUM UVIS F631N FLASH=21 1 350 S (350 S 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 F606W none none none none 1 N/A S OMEGACEN 2 WFC3/UVI ACCUM UVIS F621M none none none none 1 N/A S OMEGACEN 3 WFC3/UVI ACCUM UVIS F656N none none none none 1 N/A S OMEGACEN 4 WFC3/UVI ACCUM UVIS F502N none none none none 1 N/A S OMEGACEN 5 WFC3/UVI ACCUM UVIS F657N none none none none 1 N/A S OMEGACEN 6 WFC3/UVI ACCUM UVIS F631N none none none none 1 N/A S 17693( 4) - 17-Apr-2025 15:47:32 - [ 7] Visit: 04 (Visit 04 F160W) Visit Requirements: PCS MODE FINE; ORIENT 291.5D TO 291.5 D; BETWEEN 01-JAN-2026:00:00:00 AND 30-MAR-2026:00:00:00 On Hold Comments: Additional Comments: 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/IR MULTIAC IR F160W SAMP-SEQ=SPARS25, NSAMP=11 1 DEF EXP PCS MODE FINE CUM (252.937 S) ------------------------------------------------------------------------------------------------------------------------------------ 2 OMEGACEN WFC3/IR MULTIAC IR F130N SAMP-SEQ=SPARS25, NSAMP=11 1 DEF EXP PCS MODE FINE CUM (252.937 S) ------------------------------------------------------------------------------------------------------------------------------------ 3 OMEGACEN WFC3/IR MULTIAC IR F132N SAMP-SEQ=SPARS25, NSAMP=11 1 DEF EXP PCS MODE FINE CUM (252.937 S) ------------------------------------------------------------------------------------------------------------------------------------ 4 OMEGACEN WFC3/IR MULTIAC IR F126N SAMP-SEQ=SPARS25, NSAMP=11 1 DEF EXP PCS MODE FINE CUM (252.937 S) ------------------------------------------------------------------------------------------------------------------------------------ 5 OMEGACEN WFC3/IR MULTIAC IR F139M SAMP-SEQ=SPARS25, NSAMP=11 1 DEF EXP PCS MODE FINE CUM (252.937 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/IR MULTIAC IR F160W none none none none 1 N/A CUM OMEGACEN 2 WFC3/IR MULTIAC IR F130N none none none none 1 N/A CUM OMEGACEN 3 WFC3/IR MULTIAC IR F132N none none none none 1 N/A CUM OMEGACEN 4 WFC3/IR MULTIAC IR F126N none none none none 1 N/A CUM OMEGACEN 5 WFC3/IR MULTIAC IR F139M none none none none 1 N/A CUM 17693( 4) - 17-Apr-2025 15:47:32 - [ 8] Visit: 05 (Visit 05 F160W) Visit Requirements: PCS MODE FINE; ORIENT 293D TO 293 D; BETWEEN 01-JAN-2026:00:00:00 AND 31-MAR-2026:00:00:00 On Hold Comments: Additional Comments: 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/IR MULTIAC IR F160W SAMP-SEQ=SPARS25, NSAMP=11 1 DEF EXP PCS MODE FINE CUM (252.937 S) ------------------------------------------------------------------------------------------------------------------------------------ 2 OMEGACEN WFC3/IR MULTIAC IR F128N SAMP-SEQ=SPARS25, NSAMP=11 1 DEF EXP PCS MODE FINE CUM (252.937 S) ------------------------------------------------------------------------------------------------------------------------------------ 3 OMEGACEN WFC3/IR MULTIAC IR F167N SAMP-SEQ=SPARS25, NSAMP=11 1 DEF EXP PCS MODE FINE CUM (252.937 S) ------------------------------------------------------------------------------------------------------------------------------------ 4 OMEGACEN WFC3/IR MULTIAC IR F164N SAMP-SEQ=SPARS25, NSAMP=12 1 DEF EXP PCS MODE FINE CUM (277.938 S) ------------------------------------------------------------------------------------------------------------------------------------ 5 OMEGACEN WFC3/UVI ACCUM UVIS F673N FLASH=21 1 350 S (350 S S) ------------------------------------------------------------------------------------------------------------------------------------ 6 OMEGACEN WFC3/UVI ACCUM UVIS F953N FLASH=21 1 350 S (350 S 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/IR MULTIAC IR F160W none none none none 1 N/A CUM OMEGACEN 2 WFC3/IR MULTIAC IR F128N none none none none 1 N/A CUM OMEGACEN 3 WFC3/IR MULTIAC IR F167N none none none none 1 N/A CUM OMEGACEN 4 WFC3/IR MULTIAC IR F164N none none none none 1 N/A CUM OMEGACEN 5 WFC3/UVI ACCUM UVIS F673N none none none none 1 N/A S OMEGACEN 6 WFC3/UVI ACCUM UVIS F953N none none none none 1 N/A S 17693( 4) - 17-Apr-2025 15:47:32 - [ 9] Visit: 06 (Visit 06 F160W) Visit Requirements: PCS MODE FINE; ORIENT 294.5D TO 294.5 D; BETWEEN 01-JAN-2026:00:00:00 AND 31-MAR-2026:00:00:00 On Hold Comments: Additional Comments: 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/IR MULTIAC IR F160W SAMP-SEQ=SPARS25, NSAMP=11 1 DEF EXP PCS MODE FINE CUM (252.937 S) ------------------------------------------------------------------------------------------------------------------------------------ 2 OMEGACEN WFC3/UVI ACCUM UVIS F395N FLASH=21 1 350 S (350 S S) ------------------------------------------------------------------------------------------------------------------------------------ 3 OMEGACEN WFC3/UVI ACCUM UVIS F658N FLASH=21 1 350 S (350 S S) ------------------------------------------------------------------------------------------------------------------------------------ 4 OMEGACEN WFC3/UVI ACCUM UVIS F343N FLASH=21 1 350 S (350 S 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/IR MULTIAC IR F160W none none none none 1 N/A CUM OMEGACEN 2 WFC3/UVI ACCUM UVIS F395N none none none none 1 N/A S OMEGACEN 3 WFC3/UVI ACCUM UVIS F658N none none none none 1 N/A S OMEGACEN 4 WFC3/UVI ACCUM UVIS F343N none none none none 1 N/A S 17693( 4) - 17-Apr-2025 15:47:32 - [ 10] Summary Form for Proposal 17693 Item Used in this proposal ------------------------------------------------------------------------------------------------------------------------------------ Apertures IR, UVIS ------------------------------------------------------------------------------------------------------------------------------------ Configurations WFC3/IR, WFC3/UVIS ------------------------------------------------------------------------------------------------------------------------------------ Opmodes ACCUM, MULTIACCUM ------------------------------------------------------------------------------------------------------------------------------------ Optional Parameters FLASH=12, FLASH=14, FLASH=21, NSAMP=11, NSAMP=12, SAMP-SEQ=SPARS25 ------------------------------------------------------------------------------------------------------------------------------------ Special Requirements BETWEEN 01-JAN-2026:00:00:00 AND 30-MAR-2026:00:00:00, BETWEEN 01-JAN-2026:00:00:00 AND 31-MAR-2026:00:00:00, EXP PCS MODE FINE, ORIENT 284D TO 284 D, ORIENT 285.5D TO 285.5 D, ORIENT 287D TO 287 D, ORIENT 291.5D TO 291.5 D, ORIENT 293D TO 293 D, ORIENT 294.5D TO 294.5 D, PCS MODE FINE ------------------------------------------------------------------------------------------------------------------------------------ Spectral Elements F126N, F128N, F130N, F132N, F139M, F160W, F164N, F167N, F218W, F225W, F343N, F390W, F395N, F475W, F502N, F547M, F555W, F606W, F621M, F625W, F631N, F656N, F657N, F658N, F673N, F763M, F775W, F845M, F953N ------------------------------------------------------------------------------------------------------------------------------------ Target Names OMEGACEN ------------------------------------------------------------------------------------------------------------------------------------