18418( 3) - 19-Aug-2026 15:07:05 - [ 1] HUBBLE SPACE TELESCOPE OBSERVING PROGRAM 18418 Version: 3 Check-in Time: 19-Aug-2026 15:07:05 STScI Edit Number: 0 Title A Far-UV Type II Supernova Treasury for the Upcoming UVEX Mission ------------------------------------------------------------------------------------ Type Cycle GO 34 ------------------------------------------------------------------------------------ Investigators Contact? PI: Dr. Wynn Vicente Jacobson-Galan California Institute of Technology Y CoI: Dr. Luc Dessart CNRS, Institut d'Astrophysique de Paris N CoI: Dr. Mansi Kasliwal California Institute of Technology N CoI: Dr. Raffaella Margutti University of California - Berkeley N CoI: Dr. Suvi Gezari University of Maryland N CoI: Prof. Ryan Chornock University of California - Berkeley N CoI: Mr. Kaustav Kashyap Das California Institute of Technology N CoI: Dr. Michael W. Coughlin University of Minnesota - Twin Cities N CoI: Aaron Tohuvavohu California Institute of Technology N CoI: Dr. Anthony Piro Carnegie Institution of Washington N ------------------------------------------------------------------------------------ Abstract Ultraviolet (UV) spectroscopy of young type II supernovae (SNe II) in the first weeks post-explosion remains an almost completely unconstrained observational phase space. To date, only 2 published SNe II have been observed in far-UV (<1600 Angstroms) wavelengths in the first week post-explosion and no SN II with spectroscopic signatures of CSM-interaction at such wavelengths. In anticipation of the planned launch of the Ultraviolet Explorer (UVEX) NASA mission, we propose a disruptive ToO program to obtain FUV/NUV spectroscopy of 2 SNe II within their first 1-2 weeks post-explosion. This collection of STIS MAMAS (G140L and G230L gratings) observations will increase the number of young SNe II with FUV HST spectra by a factor of 2 and create a legacy UV dataset necessary for UVEX preparation. HST UV spectroscopy will enable robust constraints to be made on the chemical composition, density and extent of the progenitor star wind as well as the mechanisms for enhanced mass-loss in red supergiants during their final years. Furthermore, these observations will directly inform the creation of physically consistent non-LTE radiative transfer models of young SNe II that can be used to robustly interpret the large number of FUV SN II spectra expected from the UVEX mission. ------------------------------------------------------------------------------------ Observations Description ------------------------ Far- and near-UV spectroscopy observations with STIS/MAMAS of two type II supernovae. Each target will need 3 epochs of observations (2 orbits per obs.). The first observation for each supernova should occur as soon after the ToO trigger as possible. The second and third epochs should occur ~2 days and ~4 days after the first epoch. Far and near-UV spectra observations per epoch need to be linked. ------------------------------------------------------------------------------------ 18418( 3) - 19-Aug-2026 15:07:05 - [ 2] TARGET LIST Generic Targets ------------------------------------------------------------------------------------------------------------------------------------ Tar| Target | Target | Selection Criteria | Flux data No | Name | Description | | ------------------------------------------------------------------------------------------------------------------------------------ 1 SNII-1 EXT-STAR, SUPERNOVA CSM INTERACTING SN II V = 17 TYPE II ------------------------------------------------------------------------------------------------------------------------------------ 2 SNII-2 EXT-STAR, SUPERNOVA CSM INTERACTING SN II V = 17 TYPE II ------------------------------------------------------------------------------------------------------------------------------------ 18418( 3) - 19-Aug-2026 15:07:05 - [ 3] Visit: 01 (SN II 1 FUV + NUV -- Epoch 1) Visit Requirements: ON HOLD ; TOO MIN RESPONSE TIME 2.0D; TOO MAX RESPONSE TIME 3.0D On Hold Comments: ToO activation -- maximum response time is optimistic and can be iterated on. We hope for observations as soon as possible after trigger. Additional Comments: First epoch for target 1 -- needs to be observed as soon as possible after trigger (within the constraints of disruptive ToO policy). 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 SNII-1 STIS/CCD ACQ F28X50LP MIRROR 1 5 S (5 S) ------------------------------------------------------------------------------------------------------------------------------------ 2 SNII-1 STIS/FUV ACCUM 52X0.2 G140L 1425 1 2090 S -MAMA (2090 S) ------------------------------------------------------------------------------------------------------------------------------------ 3 SNII-1 STIS/CCD ACQ F28X50LP MIRROR 1 5 S (5 S) ------------------------------------------------------------------------------------------------------------------------------------ 4 SNII-1 STIS/NUV ACCUM 52X0.2 G230L 2376 1 1856 S -MAMA (1856 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 | ------------------------------------------------------------------------------------------------------------------------------------ SNII-1 1 STIS/CCD ACQ F28X50LP MIRROR none none none none 1 N/A SNII-1 2 STIS/FUV ACCUM 52X0.2 G140L 1425 none none none none 1 N/A -MAMA SNII-1 3 STIS/CCD ACQ F28X50LP MIRROR none none none none 2 N/A SNII-1 4 STIS/NUV ACCUM 52X0.2 G230L 2376 none none none none 2 N/A -MAMA 18418( 3) - 19-Aug-2026 15:07:05 - [ 4] Visit: 02 (SN II 1 FUV+NUV -- Epoch 2) Visit Requirements: ON HOLD ; TOO MIN RESPONSE TIME 2.0D; TOO MAX RESPONSE TIME 3.0D On Hold Comments: ToO activation Additional Comments: Second epoch for target 1 -- needs to be within 1-2 days of the first epoch. 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 SNII-1 STIS/CCD ACQ F28X50LP MIRROR 1 5 S (5 S) ------------------------------------------------------------------------------------------------------------------------------------ 2 SNII-1 STIS/FUV ACCUM 52X0.2 G140L 1425 1 2090 S -MAMA (2090 S) ------------------------------------------------------------------------------------------------------------------------------------ 3 SNII-1 STIS/CCD ACQ F28X50LP MIRROR 1 5 S (5 S) ------------------------------------------------------------------------------------------------------------------------------------ 4 SNII-1 STIS/NUV ACCUM 52X0.2 G230L 2376 1 1856 S -MAMA (1856 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 | ------------------------------------------------------------------------------------------------------------------------------------ SNII-1 1 STIS/CCD ACQ F28X50LP MIRROR none none none none 1 N/A SNII-1 2 STIS/FUV ACCUM 52X0.2 G140L 1425 none none none none 1 N/A -MAMA SNII-1 3 STIS/CCD ACQ F28X50LP MIRROR none none none none 2 N/A SNII-1 4 STIS/NUV ACCUM 52X0.2 G230L 2376 none none none none 2 N/A -MAMA 18418( 3) - 19-Aug-2026 15:07:05 - [ 5] Visit: 03 (SN II 1 FUV+NUV -- Epoch 3) Visit Requirements: ON HOLD ; TOO MIN RESPONSE TIME 2.0D; TOO MAX RESPONSE TIME 3.0D On Hold Comments: ToO activation Additional Comments: Third epoch for target 1 -- needs to be within 1-2 days of the second epoch. 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 SNII-1 STIS/CCD ACQ F28X50LP MIRROR 1 5 S (5 S) ------------------------------------------------------------------------------------------------------------------------------------ 2 SNII-1 STIS/FUV ACCUM 52X0.2 G140L 1425 1 2090 S -MAMA (2090 S) ------------------------------------------------------------------------------------------------------------------------------------ 3 SNII-1 STIS/CCD ACQ F28X50LP MIRROR 1 5 S (5 S) ------------------------------------------------------------------------------------------------------------------------------------ 4 SNII-1 STIS/NUV ACCUM 52X0.2 G230L 2376 1 1856 S -MAMA (1856 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 | ------------------------------------------------------------------------------------------------------------------------------------ SNII-1 1 STIS/CCD ACQ F28X50LP MIRROR none none none none 1 N/A SNII-1 2 STIS/FUV ACCUM 52X0.2 G140L 1425 none none none none 1 N/A -MAMA SNII-1 3 STIS/CCD ACQ F28X50LP MIRROR none none none none 2 N/A SNII-1 4 STIS/NUV ACCUM 52X0.2 G230L 2376 none none none none 2 N/A -MAMA 18418( 3) - 19-Aug-2026 15:07:05 - [ 6] Visit: 04 (SN II 2 FUV+NUV -- Epoch 1) Visit Requirements: ON HOLD ; TOO MIN RESPONSE TIME 2.0D; TOO MAX RESPONSE TIME 3.0D On Hold Comments: ToO Activation Additional Comments: First epoch for target 2 -- needs to be observed as soon as possible after trigger (within the constraints of disruptive ToO policy). 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 SNII-2 STIS/CCD ACQ F28X50LP MIRROR 1 5 S (5 S) ------------------------------------------------------------------------------------------------------------------------------------ 2 SNII-2 STIS/FUV ACCUM 52X0.2 G140L 1425 1 2090 S -MAMA (2090 S) ------------------------------------------------------------------------------------------------------------------------------------ 3 SNII-2 STIS/CCD ACQ F28X50LP MIRROR 1 5 S (5 S) ------------------------------------------------------------------------------------------------------------------------------------ 4 SNII-2 STIS/NUV ACCUM 52X0.2 G230L 2376 1 1856 S -MAMA (1856 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 | ------------------------------------------------------------------------------------------------------------------------------------ SNII-2 1 STIS/CCD ACQ F28X50LP MIRROR none none none none 1 N/A SNII-2 2 STIS/FUV ACCUM 52X0.2 G140L 1425 none none none none 1 N/A -MAMA SNII-2 3 STIS/CCD ACQ F28X50LP MIRROR none none none none 2 N/A SNII-2 4 STIS/NUV ACCUM 52X0.2 G230L 2376 none none none none 2 N/A -MAMA 18418( 3) - 19-Aug-2026 15:07:05 - [ 7] Visit: 05 (SN II 2 FUV+NUV -- Epoch 2) Visit Requirements: ON HOLD ; TOO MIN RESPONSE TIME 2.0D; TOO MAX RESPONSE TIME 3.0D On Hold Comments: ToO Additional Comments: Second epoch for target 2 -- needs to be within 1-2 days of the first epoch. 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 SNII-2 STIS/CCD ACQ F28X50LP MIRROR 1 5 S (5 S) ------------------------------------------------------------------------------------------------------------------------------------ 2 SNII-2 STIS/FUV ACCUM 52X0.2 G140L 1425 1 2090 S -MAMA (2090 S) ------------------------------------------------------------------------------------------------------------------------------------ 3 SNII-2 STIS/CCD ACQ F28X50LP MIRROR 1 5 S (5 S) ------------------------------------------------------------------------------------------------------------------------------------ 4 SNII-2 STIS/NUV ACCUM 52X0.2 G230L 2376 1 1856 S -MAMA (1856 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 | ------------------------------------------------------------------------------------------------------------------------------------ SNII-2 1 STIS/CCD ACQ F28X50LP MIRROR none none none none 1 N/A SNII-2 2 STIS/FUV ACCUM 52X0.2 G140L 1425 none none none none 1 N/A -MAMA SNII-2 3 STIS/CCD ACQ F28X50LP MIRROR none none none none 2 N/A SNII-2 4 STIS/NUV ACCUM 52X0.2 G230L 2376 none none none none 2 N/A -MAMA 18418( 3) - 19-Aug-2026 15:07:05 - [ 8] Visit: 06 (SN II 2 FUV+NUV -- Epoch 3) Visit Requirements: ON HOLD ; TOO MIN RESPONSE TIME 2.0D; TOO MAX RESPONSE TIME 3.0D On Hold Comments: ToO Additional Comments: Third epoch for target 2 -- needs to be within 1-2 days of the second epoch. 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 SNII-2 STIS/CCD ACQ F28X50LP MIRROR 1 5 S (5 S) ------------------------------------------------------------------------------------------------------------------------------------ 2 SNII-2 STIS/FUV ACCUM 52X0.2 G140L 1425 1 2090 S -MAMA (2090 S) ------------------------------------------------------------------------------------------------------------------------------------ 3 SNII-2 STIS/CCD ACQ F28X50LP MIRROR 1 5 S (5 S) ------------------------------------------------------------------------------------------------------------------------------------ 4 SNII-2 STIS/NUV ACCUM 52X0.2 G230L 2376 1 1856 S -MAMA (1856 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 | ------------------------------------------------------------------------------------------------------------------------------------ SNII-2 1 STIS/CCD ACQ F28X50LP MIRROR none none none none 1 N/A SNII-2 2 STIS/FUV ACCUM 52X0.2 G140L 1425 none none none none 1 N/A -MAMA SNII-2 3 STIS/CCD ACQ F28X50LP MIRROR none none none none 2 N/A SNII-2 4 STIS/NUV ACCUM 52X0.2 G230L 2376 none none none none 2 N/A -MAMA 18418( 3) - 19-Aug-2026 15:07:05 - [ 9] Summary Form for Proposal 18418 Item Used in this proposal ------------------------------------------------------------------------------------------------------------------------------------ Apertures 52X0.2, F28X50LP ------------------------------------------------------------------------------------------------------------------------------------ Configurations STIS/CCD, STIS/FUV-MAMA, STIS/NUV-MAMA ------------------------------------------------------------------------------------------------------------------------------------ Opmodes ACCUM, ACQ ------------------------------------------------------------------------------------------------------------------------------------ Optional Parameters ------------------------------------------------------------------------------------------------------------------------------------ Special Requirements ON HOLD , TOO MAX RESPONSE TIME 3.0D, TOO MIN RESPONSE TIME 2.0D ------------------------------------------------------------------------------------------------------------------------------------ Spectral Elements G140L, G230L, MIRROR ------------------------------------------------------------------------------------------------------------------------------------ Target Names SNII-1, SNII-2 ------------------------------------------------------------------------------------------------------------------------------------