18008( 5) - 30-Mar-2026 16:10:23 - [ 1] HUBBLE SPACE TELESCOPE OBSERVING PROGRAM 18008 Version: 5 Check-in Time: 30-Mar-2026 16:10:23 STScI Edit Number: 1 Title Using HST to Find Supernova Progenitor Stars in JWST, HST, and Euclid Imaging ------------------------------------------------------------------------------------ Type Cycle GO 33 ------------------------------------------------------------------------------------ Investigators Contact? PI: Dr. Charles Kilpatrick Northwestern University Y CoI: Prof. Ryan Foley University of California - Santa Cruz N CoI: Dr. Kirsty Taggart University of California - Santa Cruz N CoI: Dr. Wynn Vicente Jacobson-Galan California Institute of Technology N CoI: jason vazquez University of Illinois at Urbana - N Champaign CoI: Dr. Alexander Thomas Gagliano Massachusetts Institute of Technology N CoI: Kyle Davis University of California - Santa Cruz N ------------------------------------------------------------------------------------ Abstract Supernovae and other luminous transients at <40 Mpc often have deep, high-resolution pre-explosion imaging in which a single progenitor system can be isolated. The vast archives of multi-band, multi-epoch HST imaging have revolutionized this field over the past 25 years, but as new missions such as JWST and Euclid come online, more such examples will be found. Each new event is extremely valuable for studying the correlation between supernova properties and the mass, metallicity, and local environments of the specific stars that explode. However, the fields where these occur are crowded, and often multiple candidate counterparts are found to the limits of natural seeing in pre-explosion imaging. A follow-up, high-resolution image is typically needed, and this is often impossible to obtain from the ground with adaptive optics due to the lack of proper bright guide stars that are needed within ~30 arcseconds. In these cases, we will trigger a non-disruptive HST target-of-opportunity observation to obtain the necessary high-resolution imaging and isolate the individual star that exploded. With 2 such triggers during Cycle 33, we can catch supernovae and isolate their progenitor systems in pre-explosion imaging, catching these rare and valuable events as they occur in the nearby Universe. ------------------------------------------------------------------------------------ Observations Description ------------------------ This is a target-of-opportunity proposal to observe up to 2 supernovae at <40 Mpc with pre-explosion JWST, HST, and/or Euclid imaging. The goal of the proposal is to obtain imaging at the site of each supernova in order to precisely align to the pre-explosion imaging and identify or rule out the presence of a counterpart in the pre-explosion data. We are requesting a 3 week minimum response time from the time of trigger in order to guarantee that we can calibrate our exposures to the expected brightness of the supernova at the time of observation and avoid either saturating or failing to detect the primary supernova target. Our fiducial observation setup assumes that we will observe the supernova 18008( 5) - 30-Mar-2026 16:10:23 - [ 2] around or slightly after maximum light, with a required brightness of >16.5 mag to avoid saturating this source, which would limit the astrometric precision in centroiding on the supernova. We therefore use 68s exposures in F555W and use the UVIS2-C1K1C-SUB readout mode to reduce overheads between individual exposures. As we are targeting sources in galaxies at <40 Mpc, we expect the field around the supernova to be crowded with astrometric calibrators, and so the smaller readout region will not limit our science case. We have also adjusted FLASH=15 to avoid CTE losses. To improve PSF sampling, we use 4 iterations of a WFC3-UVIS-DITHER-BOX pattern for a total of 16 individual exposures. ------------------------------------------------------------------------------------ 18008( 5) - 30-Mar-2026 16:10:23 - [ 3] TARGET LIST Fixed Targets ------------------------------------------------------------------------------------------------------------------------------------ Tar| Target | Target | Target |Coord | Radial | Flux data No | Name | Description | Position |Eqnx | Vel. | ------------------------------------------------------------------------------------------------------------------------------------ 3 SN2026DIX EXT-STAR, SUPERNOVA RA=11H50M37.4300S, J2000 V = 16.5 DEC=+55D21'12.92" Reference Frame: ICRS Extended: NO ------------------------------------------------------------------------------------------------------------------------------------ 18008( 5) - 30-Mar-2026 16:10:23 - [ 4] TARGET LIST Generic Targets ------------------------------------------------------------------------------------------------------------------------------------ Tar| Target | Target | Selection Criteria | Flux data No | Name | Description | | ------------------------------------------------------------------------------------------------------------------------------------ 2 TOO2 SECOND SUPERNOVA AT <40 MPC WITH V = 16.5 PRE-EXPLOSION IMAGING ------------------------------------------------------------------------------------------------------------------------------------ 18008( 5) - 30-Mar-2026 16:10:23 - [ 5] Patterns ------------------------------------------------------------------------------------------------------------------------------------ Pattern_Number: 1 Primary_Pattern Secondary_Pattern Pattern_Type WFC3-UVIS-DITHER-BOX Pattern_Purpose DITHER Number_Of_Points 4 Point_Spacing 0.173 Line_Spacing 0.112 Coordinate_Frame POS-TARG Pattern_Orient 23.884 Angle_Between_Sides 81.785 Center_Pattern NO ------------------------------------------------------------------------------------------------------------------------------------ 18008( 5) - 30-Mar-2026 16:10:23 - [ 6] Visit: 01 (SN2026dix) Visit Requirements: TOO RESPONSE TIME 21.0D On Hold Comments: Additional Comments: May 19 - 21 is the preferred observing window. 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 SN2026DIX WFC3/UVI ACCUM UVIS2-C1K F555W FLASH=21 4 68 S PATTERN 1 1 S 1C-SUB see below (1120 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 | ------------------------------------------------------------------------------------------------------------------------------------ SN2026DIX 1 WFC3/UVI ACCUM UVIS2-C1 F555W 1 none 1 none 1 70.0 S S K1C-SUB SN2026DIX 1 WFC3/UVI ACCUM UVIS2-C1 F555W 1 none 2 none 1 70.0 S S K1C-SUB SN2026DIX 1 WFC3/UVI ACCUM UVIS2-C1 F555W 1 none 3 none 1 70.0 S S K1C-SUB SN2026DIX 1 WFC3/UVI ACCUM UVIS2-C1 F555W 1 none 4 none 1 70.0 S S K1C-SUB SN2026DIX 1 WFC3/UVI ACCUM UVIS2-C1 F555W 2 none 1 none 1 70.0 S S K1C-SUB SN2026DIX 1 WFC3/UVI ACCUM UVIS2-C1 F555W 2 none 2 none 1 70.0 S S K1C-SUB SN2026DIX 1 WFC3/UVI ACCUM UVIS2-C1 F555W 2 none 3 none 1 70.0 S S K1C-SUB SN2026DIX 1 WFC3/UVI ACCUM UVIS2-C1 F555W 2 none 4 none 1 70.0 S S K1C-SUB SN2026DIX 1 WFC3/UVI ACCUM UVIS2-C1 F555W 3 none 1 none 1 70.0 S S K1C-SUB SN2026DIX 1 WFC3/UVI ACCUM UVIS2-C1 F555W 3 none 2 none 1 70.0 S S K1C-SUB SN2026DIX 1 WFC3/UVI ACCUM UVIS2-C1 F555W 3 none 3 none 1 70.0 S S K1C-SUB SN2026DIX 1 WFC3/UVI ACCUM UVIS2-C1 F555W 3 none 4 none 1 70.0 S S K1C-SUB SN2026DIX 1 WFC3/UVI ACCUM UVIS2-C1 F555W 4 none 1 none 1 70.0 S S K1C-SUB SN2026DIX 1 WFC3/UVI ACCUM UVIS2-C1 F555W 4 none 2 none 1 70.0 S S K1C-SUB SN2026DIX 1 WFC3/UVI ACCUM UVIS2-C1 F555W 4 none 3 none 1 70.0 S S K1C-SUB SN2026DIX 1 WFC3/UVI ACCUM UVIS2-C1 F555W 4 none 4 none 1 70.0 S S K1C-SUB 18008( 5) - 30-Mar-2026 16:10:23 - [ 7] Visit: 02 (TOO-2) Visit Requirements: ON HOLD ; TOO RESPONSE TIME 21.0D On Hold Comments: On hold until trigger on a supernova discovered at <40 Mpc with pre-explosion JWST, HST, or Euclid imaging 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 TOO2 WFC3/UVI ACCUM UVIS2-C1K F555W FLASH=21 4 68 S (1088 PATTERN 1 1 S 1C-SUB 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 | ------------------------------------------------------------------------------------------------------------------------------------ TOO2 1 WFC3/UVI ACCUM UVIS2-C1 F555W 1 none 1 none 1 N/A S K1C-SUB TOO2 1 WFC3/UVI ACCUM UVIS2-C1 F555W 1 none 2 none 1 N/A S K1C-SUB TOO2 1 WFC3/UVI ACCUM UVIS2-C1 F555W 1 none 3 none 1 N/A S K1C-SUB TOO2 1 WFC3/UVI ACCUM UVIS2-C1 F555W 1 none 4 none 1 N/A S K1C-SUB TOO2 1 WFC3/UVI ACCUM UVIS2-C1 F555W 2 none 1 none 1 N/A S K1C-SUB TOO2 1 WFC3/UVI ACCUM UVIS2-C1 F555W 2 none 2 none 1 N/A S K1C-SUB TOO2 1 WFC3/UVI ACCUM UVIS2-C1 F555W 2 none 3 none 1 N/A S K1C-SUB TOO2 1 WFC3/UVI ACCUM UVIS2-C1 F555W 2 none 4 none 1 N/A S K1C-SUB TOO2 1 WFC3/UVI ACCUM UVIS2-C1 F555W 3 none 1 none 1 N/A S K1C-SUB TOO2 1 WFC3/UVI ACCUM UVIS2-C1 F555W 3 none 2 none 1 N/A S K1C-SUB TOO2 1 WFC3/UVI ACCUM UVIS2-C1 F555W 3 none 3 none 1 N/A S K1C-SUB TOO2 1 WFC3/UVI ACCUM UVIS2-C1 F555W 3 none 4 none 1 N/A S K1C-SUB TOO2 1 WFC3/UVI ACCUM UVIS2-C1 F555W 4 none 1 none 1 N/A S K1C-SUB TOO2 1 WFC3/UVI ACCUM UVIS2-C1 F555W 4 none 2 none 1 N/A S K1C-SUB TOO2 1 WFC3/UVI ACCUM UVIS2-C1 F555W 4 none 3 none 1 N/A S K1C-SUB TOO2 1 WFC3/UVI ACCUM UVIS2-C1 F555W 4 none 4 none 1 N/A S K1C-SUB 18008( 5) - 30-Mar-2026 16:10:23 - [ 8] Summary Form for Proposal 18008 Item Used in this proposal ------------------------------------------------------------------------------------------------------------------------------------ Apertures UVIS2-C1K1C-SUB ------------------------------------------------------------------------------------------------------------------------------------ Configurations WFC3/UVIS ------------------------------------------------------------------------------------------------------------------------------------ Opmodes ACCUM ------------------------------------------------------------------------------------------------------------------------------------ Optional Parameters FLASH=21 ------------------------------------------------------------------------------------------------------------------------------------ Special Requirements ON HOLD , PATTERN 1 1, TOO RESPONSE TIME 21.0D ------------------------------------------------------------------------------------------------------------------------------------ Spectral Elements F555W ------------------------------------------------------------------------------------------------------------------------------------ Target Names SN2026DIX, TOO2 ------------------------------------------------------------------------------------------------------------------------------------