18337( 2) - 31-Aug-2026 12:08:07 - [ 1] HUBBLE SPACE TELESCOPE OBSERVING PROGRAM 18337 Version: 2 Check-in Time: 31-Aug-2026 12:08:07 STScI Edit Number: 0 Title The failed supernova candidate in the low metallicity galaxy PHL293B: Still there, but what is it? ------------------------------------------------------------------------------------ Type Cycle GO 34 ------------------------------------------------------------------------------------ Investigators Contact? PI: Dr. Nathan Smith University of Arizona Y CoI: Mr. Andrew Allan Universiteit Leiden N CoI: Dr. Jennifer Andrews NOIRLab - Gemini North (HI) N CoI: Mr. Eoin Farrell Trinity College Dublin N CoI: Dr. Andrea Mehner European Southern Observatory - Chile N ------------------------------------------------------------------------------------ Abstract The metal-poor dwarf galaxy PHL293B (23 Mpc) contained a luminous blue variable (LBV) identified by its spectrum. This source had roughly constant luminosity during 2001-2009, and was modeled as a massive LBV similar to Eta Carinae, and notably, similar to the progenitors of SN2009ip and SN2015bh. In more recent data, the source faded beyond ground-based limits, and spectral signatures of the LBV disappeared. PHL293B was proposed as the first viable candidate of a failed SN event from a massive LBV star. Subsequent HST images, however, reveal a lingering blue source at the same position. So what happened? If this was indeed a failed SN, the lingering source could be a host cluster. Or if the sudden fading marks the end of an LBV giant eruption, then characterizing its current faint post-eruption state with spectroscopy is important for two reasons: (1) We know very little about the recovery time and the physical state of massive stars after an eruption, or if they return to their pre-outburst state. (2) This object offers a cautionary tale for other failed SN candidates. Whether a failed SN or not, spectroscopy is essential for assessing the star's post-eruption state, but ground-based data cannot do this because the source is lost in galaxy light. We propose deep STIS spectroscopy to determine once and for all if the LBV disappeared as a failed SN, and 2 orbits of imaging photometry to reproiduce the Cycle 28 imaging and measure its UV/optical SED. The SED is needed to evaluate the LBVs current luminosity, or to estimate the age of the host cluster and thus the approximate initial mass of the LBV) if indeed the LBV has disappeared. ------------------------------------------------------------------------------------ Observations Description ------------------------ This program repeats earlier imaging to obtain a current epoch of photometry in several filters. The STIS observations will obtain a spectrum of the LBV that is resolved from surrounding galaxy light for the first time, both low and medium resolution. ------------------------------------------------------------------------------------ 18337( 2) - 31-Aug-2026 12:08:07 - [ 2] TARGET LIST Fixed Targets ------------------------------------------------------------------------------------------------------------------------------------ Tar| Target | Target | Target |Coord | Radial | Flux data No | Name | Description | Position |Eqnx | Vel. | ------------------------------------------------------------------------------------------------------------------------------------ 1 PHL293B-LBV EXT-STAR, LUMINOUS BLUE RA=22H30M36.7500S, J2000 V = 21.5 +/- 1 VARIABLE DEC=-00D06'39.00" Reference Frame: ICRS ------------------------------------------------------------------------------------------------------------------------------------ 18337( 2) - 31-Aug-2026 12:08:07 - [ 3] Patterns ------------------------------------------------------------------------------------------------------------------------------------ Pattern_Number: 1 Primary_Pattern Secondary_Pattern Pattern_Type WFC3-UVIS-DITHER-LINE Pattern_Purpose DITHER Number_Of_Points 2 Point_Spacing 0.145 Line_Spacing Coordinate_Frame POS-TARG Pattern_Orient 46.84 Angle_Between_Sides Center_Pattern NO ------------------------------------------------------------------------------------------------------------------------------------ Pattern_Number: 2 Primary_Pattern Secondary_Pattern Pattern_Type STIS-ALONG-SLIT Pattern_Purpose DITHER Number_Of_Points 2 Point_Spacing 0.2 Line_Spacing Coordinate_Frame POS-TARG Pattern_Orient 90.0 Angle_Between_Sides Center_Pattern NO ------------------------------------------------------------------------------------------------------------------------------------ 18337( 2) - 31-Aug-2026 12:08:07 - [ 4] Visit: 01 (VISIT 01 - WFC3) Visit Requirements: On Hold Comments: 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 PHL293B-LBV WFC3/UVI ACCUM UVIS2 F606W FLASH=12 1 200 S (400 PATTERN 1 1-2 S S) ------------------------------------------------------------------------------------------------------------------------------------ 2 PHL293B-LBV WFC3/UVI ACCUM UVIS2 F225W FLASH=18 1 690 S S (1380 S) ------------------------------------------------------------------------------------------------------------------------------------ 3 PHL293B-LBV WFC3/UVI ACCUM UVIS2 F438W FLASH=18 1 240 S (240 S S) ------------------------------------------------------------------------------------------------------------------------------------ 4 PHL293B-LBV WFC3/UVI ACCUM UVIS2 F814W FLASH=15 1 210 S PATTERN 1 4-5 S see below (430 S) ------------------------------------------------------------------------------------------------------------------------------------ 5 PHL293B-LBV WFC3/UVI ACCUM UVIS2 F336W FLASH=18 1 670 S S see below (1350 S) ------------------------------------------------------------------------------------------------------------------------------------ 6 PHL293B-LBV WFC3/UVI ACCUM UVIS2 F438W FLASH=18 1 240 S POS TARG S see below -3.4088166189286015E-4, (245 S) -1.425343380764952 ------------------------------------------------------------------------------------------------------------------------------------ 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 | ------------------------------------------------------------------------------------------------------------------------------------ PHL293B-LBV 1 WFC3/UVI ACCUM UVIS2 F606W 1 none none none 1 N/A S PHL293B-LBV 1 WFC3/UVI ACCUM UVIS2 F606W 2 none none none 1 N/A S PHL293B-LBV 2 WFC3/UVI ACCUM UVIS2 F225W 1 none none none 1 N/A S PHL293B-LBV 2 WFC3/UVI ACCUM UVIS2 F225W 2 none none none 1 N/A S PHL293B-LBV 3 WFC3/UVI ACCUM UVIS2 F438W none none none none 1 N/A S PHL293B-LBV 4 WFC3/UVI ACCUM UVIS2 F814W 1 none none none 2 215.0 S S PHL293B-LBV 4 WFC3/UVI ACCUM UVIS2 F814W 2 none none none 2 215.0 S S 18337( 2) - 31-Aug-2026 12:08:07 - [ 5] 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 | ------------------------------------------------------------------------------------------------------------------------------------ PHL293B-LBV 5 WFC3/UVI ACCUM UVIS2 F336W 1 none none none 2 675.0 S S PHL293B-LBV 5 WFC3/UVI ACCUM UVIS2 F336W 2 none none none 2 675.0 S S PHL293B-LBV 6 WFC3/UVI ACCUM UVIS2 F438W none none none none 2 245.0 S S 18337( 2) - 31-Aug-2026 12:08:07 - [ 6] Visit: 02 (VISIT 02 - STIS) Visit Requirements: On Hold Comments: 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 PHL293B-LBV STIS/CCD ACQ F25ND3 MIRROR 1 30 S (30 S) ------------------------------------------------------------------------------------------------------------------------------------ 2 WAVE STIS/CCD ACCUM 52X0.2 G430L 4300 1 DEF (0 S) ------------------------------------------------------------------------------------------------------------------------------------ 3 PHL293B-LBV STIS/CCD ACCUM 52X0.2 G430L 4300 WAVECAL=NO, CR-SPLIT=2 1 900 S PATTERN 2 3-4 see below (1824 S) ------------------------------------------------------------------------------------------------------------------------------------ 4 PHL293B-LBV STIS/CCD ACCUM 52X0.2 G430L 4300 CR-SPLIT=2, WAVECAL=NO 1 900 S see below (1824 S) ------------------------------------------------------------------------------------------------------------------------------------ 5 WAVE STIS/CCD ACCUM 52X0.2 G430L 4300 1 DEF (0 S) ------------------------------------------------------------------------------------------------------------------------------------ 6 PHL293B-LBV STIS/CCD ACCUM 52X0.2 G430L 4300 CR-SPLIT=NO, WAVECAL=NO 1 450 S see below (458 S) ------------------------------------------------------------------------------------------------------------------------------------ 7 WAVE STIS/CCD ACCUM 52X0.2 G750M 6581 1 DEF (0 S) ------------------------------------------------------------------------------------------------------------------------------------ 8 PHL293B-LBV STIS/CCD ACCUM 52X0.2 G750M 6581 CR-SPLIT=3, WAVECAL=NO 1 2439 S PATTERN 2 8-10 (4878 S) ------------------------------------------------------------------------------------------------------------------------------------ 9 PHL293B-LBV STIS/CCD ACCUM 52X0.2 G750M 6581 CR-SPLIT=3, WAVECAL=NO 1 2440 S (4880 S) ------------------------------------------------------------------------------------------------------------------------------------ 10 PHL293B-LBV STIS/CCD ACCUM 52X0.2 G750M 6581 CR-SPLIT=3, WAVECAL=NO 1 2440 S (4880 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 | ------------------------------------------------------------------------------------------------------------------------------------ PHL293B-LBV 1 STIS/CCD ACQ F25ND3 MIRROR none none none none 1 N/A WAVE 2 STIS/CCD ACCUM 52X0.2 G430L 4300 none none none none 1 N/A PHL293B-LBV 3 STIS/CCD ACCUM 52X0.2 G430L 4300 1 none none 1 1 454.0 S PHL293B-LBV 3 STIS/CCD ACCUM 52X0.2 G430L 4300 1 none none 2 1 454.0 S PHL293B-LBV 3 STIS/CCD ACCUM 52X0.2 G430L 4300 2 none none 1 2 458.0 S PHL293B-LBV 3 STIS/CCD ACCUM 52X0.2 G430L 4300 2 none none 2 2 458.0 S 18337( 2) - 31-Aug-2026 12:08:07 - [ 7] 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 | ------------------------------------------------------------------------------------------------------------------------------------ PHL293B-LBV 4 STIS/CCD ACCUM 52X0.2 G430L 4300 1 none none 1 1 454.0 S PHL293B-LBV 4 STIS/CCD ACCUM 52X0.2 G430L 4300 1 none none 2 1 454.0 S PHL293B-LBV 4 STIS/CCD ACCUM 52X0.2 G430L 4300 2 none none 1 2 458.0 S PHL293B-LBV 4 STIS/CCD ACCUM 52X0.2 G430L 4300 2 none none 2 2 458.0 S WAVE 5 STIS/CCD ACCUM 52X0.2 G430L 4300 none none none none 2 N/A PHL293B-LBV 6 STIS/CCD ACCUM 52X0.2 G430L 4300 none none none none 2 458.0 S WAVE 7 STIS/CCD ACCUM 52X0.2 G750M 6581 none none none none 3 N/A PHL293B-LBV 8 STIS/CCD ACCUM 52X0.2 G750M 6581 1 none none 1 3 N/A PHL293B-LBV 8 STIS/CCD ACCUM 52X0.2 G750M 6581 1 none none 2 3 N/A PHL293B-LBV 8 STIS/CCD ACCUM 52X0.2 G750M 6581 1 none none 3 3 N/A PHL293B-LBV 8 STIS/CCD ACCUM 52X0.2 G750M 6581 2 none none 1 6 N/A PHL293B-LBV 8 STIS/CCD ACCUM 52X0.2 G750M 6581 2 none none 2 6 N/A PHL293B-LBV 8 STIS/CCD ACCUM 52X0.2 G750M 6581 2 none none 3 6 N/A PHL293B-LBV 9 STIS/CCD ACCUM 52X0.2 G750M 6581 1 none none 1 4 N/A PHL293B-LBV 9 STIS/CCD ACCUM 52X0.2 G750M 6581 1 none none 2 4 N/A PHL293B-LBV 9 STIS/CCD ACCUM 52X0.2 G750M 6581 1 none none 3 4 N/A PHL293B-LBV 9 STIS/CCD ACCUM 52X0.2 G750M 6581 2 none none 1 7 N/A PHL293B-LBV 9 STIS/CCD ACCUM 52X0.2 G750M 6581 2 none none 2 7 N/A PHL293B-LBV 9 STIS/CCD ACCUM 52X0.2 G750M 6581 2 none none 3 7 N/A PHL293B-LBV 10 STIS/CCD ACCUM 52X0.2 G750M 6581 1 none none 1 5 N/A PHL293B-LBV 10 STIS/CCD ACCUM 52X0.2 G750M 6581 1 none none 2 5 N/A PHL293B-LBV 10 STIS/CCD ACCUM 52X0.2 G750M 6581 1 none none 3 5 N/A PHL293B-LBV 10 STIS/CCD ACCUM 52X0.2 G750M 6581 2 none none 1 8 N/A PHL293B-LBV 10 STIS/CCD ACCUM 52X0.2 G750M 6581 2 none none 2 8 N/A PHL293B-LBV 10 STIS/CCD ACCUM 52X0.2 G750M 6581 2 none none 3 8 N/A 18337( 2) - 31-Aug-2026 12:08:07 - [ 8] Summary Form for Proposal 18337 Item Used in this proposal ------------------------------------------------------------------------------------------------------------------------------------ Apertures 52X0.2, F25ND3, UVIS2 ------------------------------------------------------------------------------------------------------------------------------------ Configurations STIS/CCD, WFC3/UVIS ------------------------------------------------------------------------------------------------------------------------------------ Opmodes ACCUM, ACQ ------------------------------------------------------------------------------------------------------------------------------------ Optional Parameters CR-SPLIT=2, CR-SPLIT=3, CR-SPLIT=NO, FLASH=12, FLASH=15, FLASH=18, WAVECAL=NO ------------------------------------------------------------------------------------------------------------------------------------ Special Requirements PATTERN 1 1-2, PATTERN 1 4-5, PATTERN 2 3-4, PATTERN 2 8-10, POS TARG -3.4088166189286015E-4, -1.425343380764952 ------------------------------------------------------------------------------------------------------------------------------------ Spectral Elements F225W, F336W, F438W, F606W, F814W, G430L, G750M, MIRROR ------------------------------------------------------------------------------------------------------------------------------------ Target Names PHL293B-LBV, WAVE ------------------------------------------------------------------------------------------------------------------------------------