0 Assigned ID: 6563 ----- Attempting Submission 1 (Thu Apr 10 17:50:10 GMT 2025) ----- Submitting with ToO activation for SN2026sqf 1080707798 ----- Attempting Submission 1 (Sat Jul 19 21:07:57 GMT 2025) ----- ----- Attempting Submission 2 (Fri Aug 08 13:15:32 GMT 2025) ----- ----- Attempting Submission 3 (Mon Mar 30 15:42:29 GMT 2026) ----- ----- Attempting Submission 4 (Mon Jul 13 14:33:52 GMT 2026) ----- Using HST to Find Supernova Progenitor Stars in JWST, HST, and Euclid Imaging 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. 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 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. PI Kilpatrick is an expert in analysis of analysis of supernova progenitor stars in HST and Spitzer imaging, including archival research, data analysis, and modeling. He has written 6 papers in the last 6 years on this topic. Co-I Foley is a transient observer with significant experience using ground- and space-based observatories. He has experience in analysis of resolved stellar populations, including supernova progenitor stars of all types. He has preferred access to telescopes at Lick and Keck observatory that will be used for some of the follow up described in this proposal, including adaptive optics imaging. Co-I Davis is an expert in optical/infrared core-collapse supernova follow up and studies of core-collapse supernovae with strong circumstellar interaction. Co-I Gagliano is an expert in characterization of core-collapse supernova progenitor stars, their host galaxies, and forward modeling of their light curves and spectral energy distributions. Co-I Jacobson-Galan is an expert in follow up of supernovae of all types, characterization of their circumstellar environments, and detailed modeling of their strong shock interactions. He has written several papers on this topic over the past few years. Co-I Taggart is an expert in follow up of nearby supernovae and their characterization in Hubble Space Telescope data. Co-I Vazquez is an expert in modeling of Type II supernovae and their progenitor stars and has written a paper on the nearby SN 2019mhm within the past year. Stellar Physics and Stellar Types 6 false false false false false false false SUPPORTED EXT-STAR SUPERNOVA NO J2000 STAR SUPERNOVA J2000 WFC3/UVIS Imaging No No F555W WFC3/UVIS Imaging No No F555W POS-TARG DITHER 0.173 LINE 0.112 false false 81.785 4 23.884 WFC3-UVIS-DITHER-BOX 1 false /Users/ckilpatrick/Library/CloudStorage/Dropbox/Mac/Downloads/OP-cache/18008-v01.xml The scheduling data was generated by CASM 34.1. CASM was run in Phase II mode. May 19 - 21 is the preferred observing window. 1779186742000 126.88509868444862 (Tic-Visit :proposal-id 18008 :visit-id "01" :proposal-version -1 :trans-version "20260319" :date "09-Jul-2026 13:20:24.0" :trans-errors '(:WARNINGS 0 :ERRORS 0 :HEALTH-AND-SAFETY 0 :FATAL-ERRORS 0 :CONTINUABLE-FATALS 0) :number-of-orbits 1 :saa-model "29" :si-bright-earth-limb-angle 20.0 :data-volume 285200 :tdrss-contact-duration 0 :coron NIL ) (Tic-Obset :proposal-id 18008 :visit-id "01" :obset-id "01" :pcs-mode "FGS" ) (Tic-Orbit :proposal-id 18008 :visit-id "01" :orbit-number 1 :pcs-time 380 :si-vis-utilization 2523 :al-overhead-at-end 79 :internal-dur-at-end 348 :dark-offset NIL :dark-utilization 0 :max-dark-utilization 1920 :low-sky "N" :pcs-visibility 3044 :pcs-gap 0 ) true 1 0 /Users/ckilpatrick/Library/CloudStorage/Dropbox/Mac/Downloads/OP-cache/18008-v02.xml The scheduling data was generated by CASM 34.1. CASM was run in Phase II mode. (Tic-Visit :proposal-id 18008 :visit-id "02" :proposal-version -1 :trans-version "20260319" :date "09-Jul-2026 12:44:14.0" :trans-errors '(:WARNINGS 0 :ERRORS 0 :HEALTH-AND-SAFETY 0 :FATAL-ERRORS 0 :CONTINUABLE-FATALS 0) :number-of-orbits 1 :saa-model "29" :si-bright-earth-limb-angle 20.0 :data-volume 356496 :tdrss-contact-duration 0 :coron NIL ) (Tic-Obset :proposal-id 18008 :visit-id "02" :obset-id "02" :pcs-mode "FGS" ) (Tic-Orbit :proposal-id 18008 :visit-id "02" :orbit-number 1 :pcs-time 380 :si-vis-utilization 2646 :al-overhead-at-end 85 :internal-dur-at-end 426 :dark-offset NIL :dark-utilization 0 :max-dark-utilization 1920 :low-sky "N" :pcs-visibility 3026 :pcs-gap 0 ) true 1 0 On hold until trigger on a supernova discovered at <40 Mpc with pre-explosion JWST, HST, or Euclid imaging