18041( 7) - 11-Jun-2026 18:14:59 - [ 1] HUBBLE SPACE TELESCOPE OBSERVING PROGRAM 18041 Version: 7 Check-in Time: 11-Jun-2026 18:14:59 STScI Edit Number: 0 Title Unveiling the Progenitors of Type Ibn Supernovae with Early UV Spectroscopy ------------------------------------------------------------------------------------ Type Cycle GO 33 ------------------------------------------------------------------------------------ Investigators Contact? PI: Dr. Yize Dong Harvard University Y CoI: Dr. Ori Dosovitz Fox Space Telescope Science Institute N CoI: Prof. Ashley Villar Harvard University N CoI: Dr. Luc Dessart CNRS, Institut d'Astrophysique de Paris N CoI: Dr. Qinan Wang Massachusetts Institute of Technology N CoI: Kyle Davis University of California - Santa Cruz N CoI: Prof. Alex V. Filippenko University of California - Berkeley N CoI: Dr. Nathan Smith University of Arizona N CoI: Dr. Tamas Szalai University of Szeged N CoI: Dr. Jennifer Andrews NOIRLab - Gemini North (HI) N CoI: Prof. Griffin Hosseinzadeh University of California - San Diego N CoI: Dr. Craig Pellegrino NASA Goddard Space Flight Center N CoI: Prof. Ryan Foley University of California - Santa Cruz N CoI: Dr. Sebastian Gomez University of Texas at Austin N CoI: Kaylee Marie de Soto The Pennsylvania State University N CoI: Dr. Conor Ransome University of Arizona N CoI: Karthik Yadavalli The Pennsylvania State University N CoI: Dr. Alexander Thomas Gagliano Massachusetts Institute of Technology N CoI: Mr. Diego Andres Farias University of Copenhagen, Niels Bohr N Institute CoI: Dr. Danielle Frostig Smithsonian Institution Astrophysical N Observatory CoI: Dr. Anya Elizabeth Nugent Center for Astrophysics | Harvard & N Smithsonian CoI: Dr. Kirsty Taggart Universities Space Research Association N ------------------------------------------------------------------------------------ Abstract We propose a disruptive ToO program with HST/STIS to obtain two epochs of UV spectra of a newly discovered Type Ibn supernova (SN) within 250 Mpc. Type Ibn SNe are a rare class of fast-evolving transients that exhibit strong interaction between SN ejecta and dense circumstellar material (CSM), as evidenced by their rapidly evolving light curves and narrow helium lines in their spectra. This dense CSM likely originates from enhanced mass loss during the final years of massive star evolution, but the physical mechanisms driving this remain poorly understood. Studying Type Ibn SNe offers valuable insights into the late stages of massive star evolution and the processes that lead to their explosions--fundamental questions in transient astronomy. UV spectroscopy provides critical diagnostics of the progenitor surface composition, mass, and ejecta geometry. These properties can only be precisely constrained through UV data, enabling a comprehensive exploration of progenitor diversity and offering deeper insight into the nature of Type Ibn explosions. ------------------------------------------------------------------------------------ 18041( 7) - 11-Jun-2026 18:14:59 - [ 2] Observations Description ------------------------ We propose a disruptive ToO UV spectroscopic sequence of a newly discovered Type Ibn supernova within 250 Mpc using HST/STIS FUV and NUV MAMA detectors. The sequence will consist of two epochs separated by approximately 10 days, with the first epoch scheduled before or near the optical peak. The primary goal is to capture the UV line evolution of Type Ibn supernovae, providing insights into their progenitor systems and explosion mechanisms. The first epoch will be a disruptive Target of Opportunity, using the G140L and G230L gratings, while the second epoch, taken about 10 days later, will use the G230L grating only. ------------------------------------------------------------------------------------ 18041( 7) - 11-Jun-2026 18:14:59 - [ 3] TARGET LIST Fixed Targets ------------------------------------------------------------------------------------------------------------------------------------ Tar| Target | Target | Target |Coord | Radial | Flux data No | Name | Description | Position |Eqnx | Vel. | ------------------------------------------------------------------------------------------------------------------------------------ 2 2026OBC EXT-STAR, SUPERNOVA RA=01H07M49.4247S, J2000 Z = V = 15.5 DEC=+41D59'43.38" 0.0195 Reference Frame: ICRS Extended: NO ------------------------------------------------------------------------------------------------------------------------------------ 18041( 7) - 11-Jun-2026 18:14:59 - [ 4] TARGET LIST Generic Targets ------------------------------------------------------------------------------------------------------------------------------------ Tar| Target | Target | Selection Criteria | Flux data No | Name | Description | | ------------------------------------------------------------------------------------------------------------------------------------ 1 SN2025IBN STAR, SUPERNOVA WE WILL TRIGGER ON A NEWLY V = 17 +/- 0.5 DISCOVERED TYPE IBN SUPERNOVA ------------------------------------------------------------------------------------------------------------------------------------ 18041( 7) - 11-Jun-2026 18:14:59 - [ 5] Visit: 01 (First Epoch (NUV)) Visit Requirements: SEQ 01, 02, 03 WITHIN 2 D; ON HOLD ; TOO MIN RESPONSE TIME 2.0D; TOO MAX RESPONSE TIME 5.0D On Hold Comments: We will trigger the first epoch on a newly discovered Type Ibn supernova. We understand that the stated response time represents a lower limit on what STScI can accommodate, but an earlier observation would maximize the information we can obtain about the progenitor system. Additional Comments: We will trigger the program on a newly discovered Type Ibn supernova within 250 Mpc 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 2026OBC STIS/CCD ACQ F28X50LP MIRROR 1 22 S (22 S) ------------------------------------------------------------------------------------------------------------------------------------ 2 2026OBC STIS/NUV TIME-TA 52X0.2 G230L 2376 BUFFER-TIME=1821 1 2000 S -MAMA G (2000 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 | ------------------------------------------------------------------------------------------------------------------------------------ 2026OBC 1 STIS/CCD ACQ F28X50LP MIRROR none none none none 1 N/A 2026OBC 2 STIS/NUV TIME-TA 52X0.2 G230L 2376 none none none none 1 N/A -MAMA G 18041( 7) - 11-Jun-2026 18:14:59 - [ 6] Visit: 02 (First Epoch (FUV_1)) Visit Requirements: SEQ 01, 02, 03 WITHIN 2 D; ON HOLD ; TOO MIN RESPONSE TIME 2.0D; TOO MAX RESPONSE TIME 5.0D On Hold Comments: We will trigger the first epoch on a newly discovered Type Ibn supernova. We understand that the stated response time represents a lower limit on what STScI can accommodate, but an earlier observation would maximize the information we can obtain about the progenitor system. Additional Comments: We will trigger the program on a newly discovered Type Ibn supernova within 250 Mpc 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 2026OBC STIS/CCD ACQ F28X50LP MIRROR 1 22 S (22 S) ------------------------------------------------------------------------------------------------------------------------------------ 2 2026OBC STIS/FUV TIME-TA 52X0.2 G140L 1425 BUFFER-TIME=7681 1 2000 S -MAMA G (2000 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 | ------------------------------------------------------------------------------------------------------------------------------------ 2026OBC 1 STIS/CCD ACQ F28X50LP MIRROR none none none none 1 N/A 2026OBC 2 STIS/FUV TIME-TA 52X0.2 G140L 1425 none none none none 1 N/A -MAMA G 18041( 7) - 11-Jun-2026 18:14:59 - [ 7] Visit: 03 (First Epoch (FUV_2)) Visit Requirements: SEQ 01, 02, 03 WITHIN 2 D; ON HOLD ; TOO MIN RESPONSE TIME 2.0D; TOO MAX RESPONSE TIME 5.0D On Hold Comments: We will trigger the first epoch on a newly discovered Type Ibn supernova. We understand that the stated response time represents a lower limit on what STScI can accommodate, but an earlier observation would maximize the information we can obtain about the progenitor system. Additional Comments: We will trigger the program on a newly discovered Type Ibn supernova within 250 Mpc 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 2026OBC STIS/CCD ACQ F28X50LP MIRROR 1 22 S (22 S) ------------------------------------------------------------------------------------------------------------------------------------ 2 2026OBC STIS/FUV TIME-TA 52X0.2 G140L 1425 BUFFER-TIME=7681 1 2000 S -MAMA G (2000 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 | ------------------------------------------------------------------------------------------------------------------------------------ 2026OBC 1 STIS/CCD ACQ F28X50LP MIRROR none none none none 1 N/A 2026OBC 2 STIS/FUV TIME-TA 52X0.2 G140L 1425 none none none none 1 N/A -MAMA G 18041( 7) - 11-Jun-2026 18:14:59 - [ 8] Visit: 04 (Second Epoch (NUV_1)) Visit Requirements: AFTER 01 BY 6 D TO 12 D; SEQ 04, 05, 06 WITHIN 2 D; ON HOLD On Hold Comments: The second visit will be taken around 10d after the first visit Additional Comments: We will trigger the program on a newly discovered Type Ibn supernova within 250 Mpc 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 2026OBC STIS/CCD ACQ F28X50LP MIRROR 1 54 S (54 S) ------------------------------------------------------------------------------------------------------------------------------------ 2 2026OBC STIS/NUV TIME-TA 52X0.2 G230L 2376 BUFFER-TIME=1928 1 1850 S -MAMA G (1850 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 | ------------------------------------------------------------------------------------------------------------------------------------ 2026OBC 1 STIS/CCD ACQ F28X50LP MIRROR none none none none 1 N/A 2026OBC 2 STIS/NUV TIME-TA 52X0.2 G230L 2376 none none none none 1 N/A -MAMA G 18041( 7) - 11-Jun-2026 18:14:59 - [ 9] Visit: 05 (Second Epoch (NUV_2)) Visit Requirements: SEQ 04, 05, 06 WITHIN 2 D; ON HOLD On Hold Comments: The second visit will be taken around 10d after the first visit Additional Comments: We will trigger the program on a newly discovered Type Ibn supernova within 250 Mpc 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 2026OBC STIS/CCD ACQ F28X50LP MIRROR 1 54 S (54 S) ------------------------------------------------------------------------------------------------------------------------------------ 2 2026OBC STIS/NUV TIME-TA 52X0.2 G230L 2376 BUFFER-TIME=1928 1 1850 S -MAMA G (1850 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 | ------------------------------------------------------------------------------------------------------------------------------------ 2026OBC 1 STIS/CCD ACQ F28X50LP MIRROR none none none none 1 N/A 2026OBC 2 STIS/NUV TIME-TA 52X0.2 G230L 2376 none none none none 1 N/A -MAMA G 18041( 7) - 11-Jun-2026 18:14:59 - [ 10] Visit: 06 (Second Epoch (NUV_3)) Visit Requirements: SEQ 04, 05, 06 WITHIN 2 D; ON HOLD On Hold Comments: The second visit will be taken around 10d after the first visit Additional Comments: We will trigger the program on a newly discovered Type Ibn supernova within 250 Mpc 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 2026OBC STIS/CCD ACQ F28X50LP MIRROR 1 54 S (54 S) ------------------------------------------------------------------------------------------------------------------------------------ 2 2026OBC STIS/NUV TIME-TA 52X0.2 G230L 2376 BUFFER-TIME=1928 1 1850 S -MAMA G (1850 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 | ------------------------------------------------------------------------------------------------------------------------------------ 2026OBC 1 STIS/CCD ACQ F28X50LP MIRROR none none none none 1 N/A 2026OBC 2 STIS/NUV TIME-TA 52X0.2 G230L 2376 none none none none 1 N/A -MAMA G 18041( 7) - 11-Jun-2026 18:14:59 - [ 11] Summary Form for Proposal 18041 Item Used in this proposal ------------------------------------------------------------------------------------------------------------------------------------ Apertures 52X0.2, F28X50LP ------------------------------------------------------------------------------------------------------------------------------------ Configurations STIS/CCD, STIS/FUV-MAMA, STIS/NUV-MAMA ------------------------------------------------------------------------------------------------------------------------------------ Opmodes ACQ, TIME-TAG ------------------------------------------------------------------------------------------------------------------------------------ Optional Parameters BUFFER-TIME=1821, BUFFER-TIME=1928, BUFFER-TIME=7681 ------------------------------------------------------------------------------------------------------------------------------------ Special Requirements AFTER 01 BY 6 D TO 12 D, ON HOLD , SEQ 01, 02, 03 WITHIN 2 D, SEQ 04, 05, 06 WITHIN 2 D, TOO MAX RESPONSE TIME 5.0D, TOO MIN RESPONSE TIME 2.0D ------------------------------------------------------------------------------------------------------------------------------------ Spectral Elements G140L, G230L, MIRROR ------------------------------------------------------------------------------------------------------------------------------------ Target Names 2026OBC ------------------------------------------------------------------------------------------------------------------------------------