The list of Investigators does not match the STScI records for this program. 0 ----- Attempting Submission 1 (Fri Aug 01 16:47:12 GMT 2025) ----- Removed Debopam Som as co-I due to transfer from WFC3 to COS. WFC3 IR Time Dependent Sensitivity: Spatial Scans We aim to measure the time dependent sensitivity loss for WFC3/IR using spatial scans of the open cluster M35. We use spatial scanning as the SNR achieved from scanning is higher than conventional staring observations. The spatial scans build on the F098M and F140W observations performed in HST programs 17684, 17586, 17261, 16439, 16031, and 14020 (F140W only). Pre-RGM, programs were designed to execute two identical visits ~3 months apart, however this is not currently feasible because RGM constrains the target visibility. Instead, we plan to execute a total of two identical visits during the window of visibility in Fall/Winter 2026. This will extend the baseline to span approximately 7 years of WFC3/IR operations, enabling high precision analysis of time-dependent sensitivity. Additionally, for both visits the short interval between each visit will provide additional sampling for the short-term repeatability. The two spatial scan visits are identical. In RGM, we can no longer observe the target in the spring (as in prior cycles). Instead we observe it in the fall (flipped by 180 degrees). Because of this, we now dither in the opposite direction compared to previous programs. Additionally, we are taking one fewer exposure than in the Cycle 32 visits due to orbital timing constraints. Therefore, observations in each visit are executed with the following strategy: - The first observation is a simple direct image in F140W. - The next 4 exposures are horizontal spatial scans (length ~13.2") in F140W with sequential dithers of 1'', perpendicular to the scan direction (the +Y direction), between exposures, as to match the experiment performed in 14020. - The following 10 exposures are performed in the same way, however with dithers of 1.4'' in the +Y direction to further mitigate persistence. - There are then 4 exposures taken with F098M, with the same 1.4" dithers in between each exposure. This puts one of the target stars at the top of the detector, thereby not allowing any further dithering in the previous direction. - Next, a large 17 arcsecond dither is performed in the +X direction (to avoid scanning on the same pixels where the star already landed), and 2 more F098M observations are taken, with subsequent dithers of 1.4" in the -Y direction. - We then switch back to F140W and take 4 more observations, with dithers of 3" in the -Y direction between exposures, as to ensure persistence is mitigated. (This is one less exposure than the corresponding Cycle 32 visits.) - Lastly, we take a dark exposure with the same sample sequence (but using 11 reads) as to characterize persistence. 0 false false RESTRICTED STELLAR CLUSTER OPEN CLUSTER This object was generated by the targetselector and retrieved from the SIMBAD database. An advantage of an open cluster is that it is not too dense like a globular, and an open cluster will contain a lot of (photometrically stable) main sequence stars. J2000 Timing link suitability includes constraints ([02 After 01 by 14.0 to 90.0 days]) The scheduling data was generated by CASM 33.1. CASM was run in Phase II mode. /Users/mmarinelli/work/WFC3/calibration/cycle33/ir-scans/OP-cache/17964-v01.xml (Tic-Visit :proposal-id 17964 :visit-id "01" :proposal-version -1 :trans-version "20250624" :date "21-Jul-2025 06:28:34.0" :trans-errors '(:WARNINGS 0 :ERRORS 0 :HEALTH-AND-SAFETY 0 :FATAL-ERRORS 0 :CONTINUABLE-FATALS 0) :number-of-orbits 1 :saa-model "30" :si-bright-earth-limb-angle 20.0 :data-volume 395344 :tdrss-contact-duration 0 :coron NIL ) (Tic-Obset :proposal-id 17964 :visit-id "01" :obset-id "01" :pcs-mode "FGS" ) (Tic-Orbit :proposal-id 17964 :visit-id "01" :orbit-number 1 :pcs-time 380 :si-vis-utilization 2459 :al-overhead-at-end 0 :internal-dur-at-end 653 :dark-offset NIL :dark-utilization 0 :max-dark-utilization 1920 :low-sky "N" :pcs-visibility 2926 :pcs-gap 0 ) true 1 0 Timing link suitability includes constraints ([02 After 01 by 14.0 to 90.0 days]) The scheduling data was generated by CASM 33.1. CASM was run in Phase II mode. /Users/mmarinelli/work/WFC3/calibration/cycle33/ir-scans/OP-cache/17964-v02.xml (Tic-Visit :proposal-id 17964 :visit-id "02" :proposal-version -1 :trans-version "20250624" :date "21-Jul-2025 06:31:19.0" :trans-errors '(:WARNINGS 0 :ERRORS 0 :HEALTH-AND-SAFETY 0 :FATAL-ERRORS 0 :CONTINUABLE-FATALS 0) :number-of-orbits 1 :saa-model "30" :si-bright-earth-limb-angle 20.0 :data-volume 395344 :tdrss-contact-duration 0 :coron NIL ) (Tic-Obset :proposal-id 17964 :visit-id "02" :obset-id "02" :pcs-mode "FGS" ) (Tic-Orbit :proposal-id 17964 :visit-id "02" :orbit-number 1 :pcs-time 380 :si-vis-utilization 2459 :al-overhead-at-end 0 :internal-dur-at-end 653 :dark-offset NIL :dark-utilization 0 :max-dark-utilization 1920 :low-sky "N" :pcs-visibility 2926 :pcs-gap 0 ) true 1 0