17963( 4) - 03-Mar-2026 14:39:09 - [ 1] HUBBLE SPACE TELESCOPE OBSERVING PROGRAM 17963 Version: 4 Check-in Time: 03-Mar-2026 14:39:09 STScI Edit Number: 1 Title WFC3 IR Time-Dependent Sensitivity: Clusters ------------------------------------------------------------------------------------ Type Cycle CAL/WFC3 33 ------------------------------------------------------------------------------------ Investigators Contact? PI: Varun Bajaj Space Telescope Science Institute Y CoI: Ms. Jennifer Mack Space Telescope Science Institute Y CoI: Ky Huynh Space Telescope Science Institute Y ------------------------------------------------------------------------------------ Abstract A variety targets/techniques result in range of IR sensitivity loss estimates. For example, the IR grism flux monitor suggests losses of 0.12+/-0.01%/yr (G102) and 0.06+/-0.01%/yr(G141). The IR photometric monitor, however, shows no strong evidence of sensitivity loss in the IR imaging filters, but the repeatability is limited by systematic errors of +/-1%. Scanned images of M35 show marginal losses 0.065+/-0.01%/yr in F140W, but these data have a large scatter which may be related to detector preconditioning. Cluster observations allow for the measurement of many more stars. We continue the monitoring of the sensitivity of the WFC3/IR channel using relative photometry of the clusters M-4 and 47 Tuc, as performed in HST programs 16864, 16512, 17260, 17363 and 17683. This program serves to complement the sensitivity change slopes from the M35 scans, G102/G141 measurements, and standard star photometric monitoring. We observe the same targets as 17683 (M4 and 47 Tuc external fields) and use similar observation strategies, though some exposures were necessarily shortened due to the reduced gyro mode effects on orbital visibility length. As M4 was imaged twice in the previous cycle, we swap to observing 47 Tuc twice and M4 once to keep a roughly balanced cadence. These observations will help constrain the time dependent sensitivity change through 2025, as well as provide a rich dataset for examining other detector behaviors. Recent analysis of these data suggest losses of 0.12+/-0.01%/yr in F110W (M4) and 0.05+/-0.05%/yr in F160W (NGC104) ------------------------------------------------------------------------------------ Observations Description ------------------------ These observations use a very similar observing strategy as seen in 17863. For the M4 visits, the two F110W exposures remain the same, however the second of the F160W exposures was shortened to fit within the shorter orbit. For 47 Tuc the dark exposure in the middle of the visit was shortened from NSAMP = 8 to NSAMP=7 to fit within the shortened orbit. The M4 visits consist of 4 exposures, starting with two F110W and ending with two F160W exposures. The F110W exposures will use the SPARS50 sample sequence 17963( 4) - 03-Mar-2026 14:39:09 - [ 2] with 14 samples. The F160W exposures will only use 13 and then 9 samples, due to the shorter orbital length due to RGM After each exposure POSTARGS of 2.5" will be applied, to mitigate self persistence. The 47 Tuc observations match the observing strategy from 17863 of alternating F160W exposures of the cluster with dark frames. Though the dark frames are unecessary for this monitoring, we keep them to specifically keep consistent detector conditions, to eliminate systematics due to observation strategy differences. However, in this cycle the penultimate dark is further shortened, to keep the same exposure times for the external images, so there is slight modification to the strategy overall. ------------------------------------------------------------------------------------ 17963( 4) - 03-Mar-2026 14:39:09 - [ 3] TARGET LIST Fixed Targets ------------------------------------------------------------------------------------------------------------------------------------ Tar| Target | Target | Target |Coord | Radial | Flux data No | Name | Description | Position |Eqnx | Vel. | ------------------------------------------------------------------------------------------------------------------------------------ 1 47TUC CALIBRATION, DETECTOR RA=00H22M27.8446S +/- 0.1", J2000 V = 22.0 LINEARITY TEST DEC=-72D04'4.75" +/- 0.1" Reference Frame: ICRS ------------------------------------------------------------------------------------------------------------------------------------ 2 M-4 STELLAR CLUSTER, RA=16H23M41.7160S, J2000 V = 5.9 GLOBULAR CLUSTER DEC=-26D30'19.01" Reference Frame: ICRS ------------------------------------------------------------------------------------------------------------------------------------ 17963( 4) - 03-Mar-2026 14:39:09 - [ 4] Visit: 01 (47Tuc Rolled) Visit Requirements: ORIENT 310D TO 318 D; BETWEEN 01-JUL-2026:00:00:00 AND 15-AUG-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 DARK WFC3/IR MULTIAC IR BLANK SAMP-SEQ=SPARS25, NSAMP=13 1 DEF GS ACQ SCENARIO BASE1O3 CUM (302.938 S) ------------------------------------------------------------------------------------------------------------------------------------ 2 47TUC WFC3/IR MULTIAC IR-FIX F160W SAMP-SEQ=SPARS10, NSAMP=10 1 DEF CUM (92.941 S) ------------------------------------------------------------------------------------------------------------------------------------ 3 DARK WFC3/IR MULTIAC IR BLANK SAMP-SEQ=SPARS50, NSAMP=15 1 DEF CUM (702.939 S) ------------------------------------------------------------------------------------------------------------------------------------ 4 47TUC WFC3/IR MULTIAC IR-FIX F160W SAMP-SEQ=SPARS25, NSAMP=15 1 DEF CUM (352.94 S) Comments: Designed to just saturate V=20 stars. ------------------------------------------------------------------------------------------------------------------------------------ 5 DARK WFC3/IR MULTIAC IR BLANK SAMP-SEQ=SPARS50, NSAMP=7 1 DEF CUM (302.935 S) ------------------------------------------------------------------------------------------------------------------------------------ 6 47TUC WFC3/IR MULTIAC IR-FIX F160W SAMP-SEQ=SPARS10, NSAMP=10 1 DEF CUM (92.941 S) ------------------------------------------------------------------------------------------------------------------------------------ 7 47TUC WFC3/IR MULTIAC IR-FIX F160W SAMP-SEQ=SPARS25, NSAMP=13 1 DEF POS TARG 4, 4 CUM (302.938 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 | ------------------------------------------------------------------------------------------------------------------------------------ DARK 1 WFC3/IR MULTIAC IR BLANK none none none none 1 N/A CUM 47TUC 2 WFC3/IR MULTIAC IR-FIX F160W none none none none 1 N/A CUM DARK 3 WFC3/IR MULTIAC IR BLANK none none none none 1 N/A CUM 47TUC 4 WFC3/IR MULTIAC IR-FIX F160W none none none none 1 N/A CUM DARK 5 WFC3/IR MULTIAC IR BLANK none none none none 1 N/A CUM 17963( 4) - 03-Mar-2026 14:39:09 - [ 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 | ------------------------------------------------------------------------------------------------------------------------------------ 47TUC 6 WFC3/IR MULTIAC IR-FIX F160W none none none none 1 N/A CUM 47TUC 7 WFC3/IR MULTIAC IR-FIX F160W none none none none 1 N/A CUM 17963( 4) - 03-Mar-2026 14:39:09 - [ 6] Visit: 02 (M-4) Visit Requirements: ORIENT 280D TO 282 D; BETWEEN 01-JAN-2026:00:00:00 AND 01-APR-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 M-4 WFC3/IR MULTIAC IR-UVIS-F F110W SAMP-SEQ=SPARS50, NSAMP=14 1 DEF POS TARG -5, 5 CUM IX (652.938 S) ------------------------------------------------------------------------------------------------------------------------------------ 2 M-4 WFC3/IR MULTIAC IR-UVIS-F F110W SAMP-SEQ=SPARS50, NSAMP=14 1 DEF POS TARG -2.5, 2.5 CUM IX (652.938 S) ------------------------------------------------------------------------------------------------------------------------------------ 3 M-4 WFC3/IR MULTIAC IR-UVIS-F F160W SAMP-SEQ=SPARS50, NSAMP=13 1 DEF POS TARG 0, 0 CUM IX (602.938 S) ------------------------------------------------------------------------------------------------------------------------------------ 4 M-4 WFC3/IR MULTIAC IR-UVIS-F F160W SAMP-SEQ=SPARS50, NSAMP=9 1 DEF POS TARG -7.5, 7.5 CUM IX (402.936 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 | ------------------------------------------------------------------------------------------------------------------------------------ M-4 1 WFC3/IR MULTIAC IR-UVIS- F110W none none none none 1 N/A CUM FIX M-4 2 WFC3/IR MULTIAC IR-UVIS- F110W none none none none 1 N/A CUM FIX M-4 3 WFC3/IR MULTIAC IR-UVIS- F160W none none none none 1 N/A CUM FIX M-4 4 WFC3/IR MULTIAC IR-UVIS- F160W none none none none 1 N/A CUM FIX 17963( 4) - 03-Mar-2026 14:39:09 - [ 7] Visit: 03 (47Tuc) Visit Requirements: ORIENT 113D TO 130 D; BETWEEN 01-JAN-2026:00:00:00 AND 01-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 DARK WFC3/IR MULTIAC IR BLANK SAMP-SEQ=SPARS25, NSAMP=13 1 DEF GS ACQ SCENARIO BASE1O3 CUM (302.938 S) ------------------------------------------------------------------------------------------------------------------------------------ 2 47TUC WFC3/IR MULTIAC IR-FIX F160W SAMP-SEQ=SPARS10, NSAMP=10 1 DEF CUM (92.941 S) ------------------------------------------------------------------------------------------------------------------------------------ 3 DARK WFC3/IR MULTIAC IR BLANK SAMP-SEQ=SPARS50, NSAMP=15 1 DEF CUM (702.939 S) ------------------------------------------------------------------------------------------------------------------------------------ 4 47TUC WFC3/IR MULTIAC IR-FIX F160W SAMP-SEQ=SPARS25, NSAMP=15 1 DEF CUM (352.94 S) Comments: Designed to just saturate V=20 stars. ------------------------------------------------------------------------------------------------------------------------------------ 5 DARK WFC3/IR MULTIAC IR BLANK SAMP-SEQ=SPARS50, NSAMP=7 1 DEF CUM (302.935 S) ------------------------------------------------------------------------------------------------------------------------------------ 6 47TUC WFC3/IR MULTIAC IR-FIX F160W SAMP-SEQ=SPARS10, NSAMP=10 1 DEF CUM (92.941 S) ------------------------------------------------------------------------------------------------------------------------------------ 7 47TUC WFC3/IR MULTIAC IR-FIX F160W SAMP-SEQ=SPARS25, NSAMP=13 1 DEF POS TARG 4, 4 CUM (302.938 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 | ------------------------------------------------------------------------------------------------------------------------------------ DARK 1 WFC3/IR MULTIAC IR BLANK none none none none 1 N/A CUM 47TUC 2 WFC3/IR MULTIAC IR-FIX F160W none none none none 1 N/A CUM DARK 3 WFC3/IR MULTIAC IR BLANK none none none none 1 N/A CUM 47TUC 4 WFC3/IR MULTIAC IR-FIX F160W none none none none 1 N/A CUM DARK 5 WFC3/IR MULTIAC IR BLANK none none none none 1 N/A CUM 17963( 4) - 03-Mar-2026 14:39:09 - [ 8] 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 | ------------------------------------------------------------------------------------------------------------------------------------ 47TUC 6 WFC3/IR MULTIAC IR-FIX F160W none none none none 1 N/A CUM 47TUC 7 WFC3/IR MULTIAC IR-FIX F160W none none none none 1 N/A CUM 17963( 4) - 03-Mar-2026 14:39:09 - [ 9] Visit: A3 (47Tuc) Visit Requirements: ORIENT 203D TO 220 D; BETWEEN 01-JAN-2026:00:00:00 AND 01-MAY-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 DARK WFC3/IR MULTIAC IR BLANK SAMP-SEQ=SPARS25, NSAMP=13 1 DEF GS ACQ SCENARIO ONEB1O3 CUM (302.938 S) ------------------------------------------------------------------------------------------------------------------------------------ 2 47TUC WFC3/IR MULTIAC IR-FIX F160W SAMP-SEQ=SPARS10, NSAMP=10 1 DEF CUM (92.941 S) ------------------------------------------------------------------------------------------------------------------------------------ 3 DARK WFC3/IR MULTIAC IR BLANK SAMP-SEQ=SPARS50, NSAMP=15 1 DEF CUM (702.939 S) ------------------------------------------------------------------------------------------------------------------------------------ 4 47TUC WFC3/IR MULTIAC IR-FIX F160W SAMP-SEQ=SPARS25, NSAMP=15 1 DEF CUM (352.94 S) Comments: Designed to just saturate V=20 stars. ------------------------------------------------------------------------------------------------------------------------------------ 5 DARK WFC3/IR MULTIAC IR BLANK SAMP-SEQ=SPARS50, NSAMP=7 1 DEF CUM (302.935 S) ------------------------------------------------------------------------------------------------------------------------------------ 6 47TUC WFC3/IR MULTIAC IR-FIX F160W SAMP-SEQ=SPARS10, NSAMP=10 1 DEF CUM (92.941 S) ------------------------------------------------------------------------------------------------------------------------------------ 7 47TUC WFC3/IR MULTIAC IR-FIX F160W SAMP-SEQ=SPARS25, NSAMP=13 1 DEF POS TARG 4, 4 CUM (302.938 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 | ------------------------------------------------------------------------------------------------------------------------------------ DARK 1 WFC3/IR MULTIAC IR BLANK none none none none 1 N/A CUM 47TUC 2 WFC3/IR MULTIAC IR-FIX F160W none none none none 1 N/A CUM DARK 3 WFC3/IR MULTIAC IR BLANK none none none none 1 N/A CUM 47TUC 4 WFC3/IR MULTIAC IR-FIX F160W none none none none 1 N/A CUM DARK 5 WFC3/IR MULTIAC IR BLANK none none none none 1 N/A CUM 17963( 4) - 03-Mar-2026 14:39:09 - [ 10] 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 | ------------------------------------------------------------------------------------------------------------------------------------ 47TUC 6 WFC3/IR MULTIAC IR-FIX F160W none none none none 1 N/A CUM 47TUC 7 WFC3/IR MULTIAC IR-FIX F160W none none none none 1 N/A CUM 17963( 4) - 03-Mar-2026 14:39:09 - [ 11] Summary Form for Proposal 17963 Item Used in this proposal ------------------------------------------------------------------------------------------------------------------------------------ Apertures IR, IR-FIX, IR-UVIS-FIX ------------------------------------------------------------------------------------------------------------------------------------ Configurations WFC3/IR ------------------------------------------------------------------------------------------------------------------------------------ Opmodes MULTIACCUM ------------------------------------------------------------------------------------------------------------------------------------ Optional Parameters NSAMP=10, NSAMP=13, NSAMP=14, NSAMP=15, NSAMP=7, NSAMP=9, SAMP-SEQ=SPARS10, SAMP-SEQ=SPARS25, SAMP-SEQ=SPARS50 ------------------------------------------------------------------------------------------------------------------------------------ Special Requirements BETWEEN 01-JAN-2026:00:00:00 AND 01-APR-2026:00:00:00, BETWEEN 01-JAN-2026:00:00:00 AND 01-MAR-2026:00:00:00, BETWEEN 01-JAN-2026:00:00:00 AND 01-MAY-2026:00:00:00, BETWEEN 01-JUL-2026:00:00:00 AND 15-AUG-2026:00:00:00, GS ACQ SCENARIO BASE1O3, GS ACQ SCENARIO ONEB1O3, ORIENT 113D TO 130 D, ORIENT 203D TO 220 D, ORIENT 280D TO 282 D, ORIENT 310D TO 318 D, POS TARG -2.5, 2.5, POS TARG -5, 5, POS TARG -7.5, 7.5, POS TARG 0, 0, POS TARG 4, 4 ------------------------------------------------------------------------------------------------------------------------------------ Spectral Elements BLANK, F110W, F160W ------------------------------------------------------------------------------------------------------------------------------------ Target Names 47TUC, DARK, M-4 ------------------------------------------------------------------------------------------------------------------------------------