18082( 5) - 04-Sep-2025 16:51:40 - [ 1] HUBBLE SPACE TELESCOPE OBSERVING PROGRAM 18082 Version: 5 Check-in Time: 04-Sep-2025 16:51:40 STScI Edit Number: 0 Title A Deeper Look at the Type Iax Supernova Remnant Pa 30 ------------------------------------------------------------------------------------ Type Cycle GO 33 ------------------------------------------------------------------------------------ Investigators Contact? PI: Dr. Tim Cunningham Harvard University Y CoI: Dr. Ilaria Caiazzo Institute of Science and Technology N Austria CoI: Dr. John Charles Raymond Smithsonian Institution Astrophysical N Observatory CoI: Dr. Scott J. Kenyon Smithsonian Institution Astrophysical N Observatory CoI: Philippe Z. Yao Princeton University N CoI: Mr. Nikolaus Zen Prusinski California Institute of Technology N CoI: Dr. Robert A. Fesen Dartmouth College N CoI: Prof. Abigail Polin Purdue University N CoI: Prof. Paul Duffell Purdue University N CoI: Prof. Shrinivas R. Kulkarni California Institute of Technology N CoI: Prof. David Charbonneau Harvard University N CoI: Prof. Eliot Quataert Princeton University N CoI: Prof. Jim Fuller California Institute of Technology N ------------------------------------------------------------------------------------ Abstract Pa 30 is an extraordinary supernova remnant harboring a central hot star with fast outflows, and showing a stunning radial filamentary morphology. The stellar remnant and the lack of hydrogen or helium suggests that the supernova was caused by a partially failed thermonuclear explosion in a white dwarf, classifying it as a type Iax supernova. This remnant offers a rare opportunity to study this new class of supernova in our own Galaxy. We here propose to complement a recently-approved Cycle 4 JWST MIRI imaging program with a deep narrowband image in [S II] of the entire nebula with HST WFC3. The proposed image will allow us to 1) study the sub-arcsecond structure of the line-emitting filaments, 2) measure with high precision the edge of the nebula in [S II], providing the first benchmark to measure the expansion of the ejecta, and 3) map with high precision, in conjunction with the JWST/MIRI image, the location and spatial extension of the filaments with respect to the dust. ------------------------------------------------------------------------------------ Observations Description ------------------------ Pa 30 is an extraordinary supernova remnant harboring a central hot star with fast outflows, and showing a stunning radial filamentary morphology. The stellar remnant and the lack of hydrogen or helium suggests that the supernova was caused by a partially failed thermonuclear explosion in a white dwarf, classifying it as a type Iax supernova. This remnant offers a rare opportunity to study this new class of supernova in our own Galaxy. We here propose to complement a recently-approved Cycle 4 JWST MIRI imaging program with a deep narrowband image in [S II] of the entire nebula with HST WFC3. The proposed 18082( 5) - 04-Sep-2025 16:51:40 - [ 2] image will allow us to 1) study the sub-arcsecond structure of the line-emitting filaments, 2) measure with high precision the edge of the nebula in [S II], providing the first benchmark to measure the expansion of the ejecta, and 3) map with high precision, in conjunction with the JWST/MIRI image, the location and spatial extension of the filaments with respect to the dust. We intend to image the full nebula over 16 orbits with WFC3 in the [S II] filter. The observations will consist of 4 unique positions, which have significant overlap, meaning that a large fraction of the nebula will be imaged in all 16 orbits. We wish to include a large number of unique rotational angles, in order to median-out diffraction spikes which will be caused by at least two bright contaminating stars within the sky footprint of the nebula. We propose to observe the entire nebula with the WFC3, using the UVIS F637N filter. Due to the 162'' x 162'' field of view of WFC3 UVIS, we can cover the entire nebula in just four pointings. We considered different configurations of the pointings in order to maximize signal-to-noise and coverage. The proposed pointings will allow to capture the full nebula and comfortably detect the outer edge of the filaments, while the overlap between the different pointings will allow us to maximize the signal to noise ratio, with at least 2 overlapping pointings in most of the nebula. Each pointing will consist of 4 orbits of observations, for a total of 16 orbits. Ideally, for each of the 4 pointings, the 4 orbits will have different position angles, such that we are able to remove diffraction spikes from a bright central contaminant. It would be ideal if among the 16 orbits, the angles cover a wide variety. We also have designed the pointings to avoid placing bright stars in the D quadrant of WFC3. To calculate the required exposure time, we analyzed the public IFU data from Keck/KCWI presented in Cunningham et al. (2024, ApJL), which cover a section of the nebula. Four orbits will allow us to detect even the faintest diffuse regions with a signal-to-noise higher than 5 with a sub-arcsecond resolution in each pointing. For the brightest, densest regions, we can achieve a higher resolution of $<$$0.5''$ with a S/N of $>$15. The choice of filter will allow us to detect all of the red-shifted doublets and most of the blue-shifted ones. Although ACS/WFC has a larger field of view, we propose to use WFC3/UVIS following the guidance in the HST Cycle 33 Call for Proposals that recommends the use of WFC3/UVIS over ACS/WFC since the latter is now only offered under shared risk. This choice is also advantageous, as WFC3/UVIS provides the narrowband F673N filter, which is perfectly suited for detecting the [S II] emission in this system. ------------------------------------------------------------------------------------ 18082( 5) - 04-Sep-2025 16:51:40 - [ 3] TARGET LIST Fixed Targets ------------------------------------------------------------------------------------------------------------------------------------ Tar| Target | Target | Target |Coord | Radial | Flux data No | Name | Description | Position |Eqnx | Vel. | ------------------------------------------------------------------------------------------------------------------------------------ 6 PA30-NE ISM, EMISSION LINE RA=00H53M17.6612S, J2000 V = 15.7 NEBULA, SNR DEC=+67D30'38.71" Reference Frame: ICRS Extended: YES Comments: North-East (NE) quadrant of nebula (52 arcsec from central star; IRAS 00500+6713). Epoch of Position RA proper motion (seconds of time/yr) DEC Proper Motion (arcsec/yr) Annual Parallax (arcsec) 2025.9 0.0 0.0 0.0 ------------------------------------------------------------------------------------------------------------------------------------ 7 PA30-NW ISM, EMISSION LINE RA=00H53M4.8520S, J2000 V = 15.7 NEBULA, SNR DEC=+67D30'38.69" Reference Frame: ICRS Extended: YES Comments: North-West (NW) quadrant of nebula (52 arcsec from central star; IRAS 00500+6713). Epoch of Position RA proper motion (seconds of time/yr) DEC Proper Motion (arcsec/yr) Annual Parallax (arcsec) 2025.9 0.0 0.0 0.0 ------------------------------------------------------------------------------------------------------------------------------------ 8 PA30-SE ISM, EMISSION LINE RA=00H53M17.6550S, J2000 V = 15.7 NEBULA, SNR DEC=+67D29'25.21" Reference Frame: ICRS Extended: YES Comments: South-East (SE) quadrant of nebula (52 arcsec from central star; IRAS 00500+6713). Epoch of Position RA proper motion (seconds of time/yr) DEC Proper Motion (arcsec/yr) Annual Parallax (arcsec) 2025.9 0.0 0.0 0.0 ------------------------------------------------------------------------------------------------------------------------------------ 9 PA30-SW ISM, EMISSION LINE RA=00H53M4.8577S, J2000 V = 15.7 NEBULA, SNR DEC=+67D29'25.20" Reference Frame: ICRS Extended: YES Comments: South-West (SW) quadrant of nebula (52 arcsec from central star; IRAS 00500+6713). Epoch of Position RA proper motion (seconds of time/yr) DEC Proper Motion (arcsec/yr) Annual Parallax (arcsec) 2025.9 0.0 0.0 0.0 ------------------------------------------------------------------------------------------------------------------------------------ 18082( 5) - 04-Sep-2025 16:51:40 - [ 4] Patterns ------------------------------------------------------------------------------------------------------------------------------------ Pattern_Number: 1 Primary_Pattern Secondary_Pattern Pattern_Type WFC3-UVIS-MOS-DITH-LINE WFC3-UVIS-MOS-DITH-LINE Pattern_Purpose MOSAIC DITHER Number_Of_Points 3 2 Point_Spacing 1.37 1.37 Line_Spacing Coordinate_Frame POS-TARG POS-TARG Pattern_Orient 85.754 33.606 Angle_Between_Sides Center_Pattern YES NO ------------------------------------------------------------------------------------------------------------------------------------ 18082( 5) - 04-Sep-2025 16:51:40 - [ 5] Visit: 01 (Pa30-NE-01) Visit Requirements: ORIENT 265D TO 272 D; ORIENT 292D TO 314 D; ORIENT 324D TO 27 D; ORIENT 37D TO 95 D 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 PA30-NE WFC3/UVI ACCUM UVIS F673N FLASH=16.0 1 1160 S PATTERN 1 1 S see below (4839 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 | ------------------------------------------------------------------------------------------------------------------------------------ PA30-NE 1 WFC3/UVI ACCUM UVIS F673N 1 1 none none 1 810 S S PA30-NE 1 WFC3/UVI ACCUM UVIS F673N 1 2 none none 1 810 S S PA30-NE 1 WFC3/UVI ACCUM UVIS F673N 2 1 none none 1 810 S S PA30-NE 1 WFC3/UVI ACCUM UVIS F673N 2 2 none none 2 803 S S PA30-NE 1 WFC3/UVI ACCUM UVIS F673N 3 1 none none 2 803 S S PA30-NE 1 WFC3/UVI ACCUM UVIS F673N 3 2 none none 2 803 S S 18082( 5) - 04-Sep-2025 16:51:40 - [ 6] Visit: 02 (Pa30-NE-02) Visit Requirements: ORIENT 265D TO 272 D; ORIENT 292D TO 314 D; ORIENT 324D TO 27 D; ORIENT 37D TO 95 D 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 PA30-NE WFC3/UVI ACCUM UVIS F673N FLASH=16.0 1 1160 S PATTERN 1 1 S see below (4839 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 | ------------------------------------------------------------------------------------------------------------------------------------ PA30-NE 1 WFC3/UVI ACCUM UVIS F673N 1 1 none none 1 810 S S PA30-NE 1 WFC3/UVI ACCUM UVIS F673N 1 2 none none 1 810 S S PA30-NE 1 WFC3/UVI ACCUM UVIS F673N 2 1 none none 1 810 S S PA30-NE 1 WFC3/UVI ACCUM UVIS F673N 2 2 none none 2 803 S S PA30-NE 1 WFC3/UVI ACCUM UVIS F673N 3 1 none none 2 803 S S PA30-NE 1 WFC3/UVI ACCUM UVIS F673N 3 2 none none 2 803 S S 18082( 5) - 04-Sep-2025 16:51:40 - [ 7] Visit: 03 (Pa30-NW-01) Visit Requirements: ORIENT 120D TO 290 D 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 PA30-NW WFC3/UVI ACCUM UVIS F673N FLASH=16.0 1 1160 S PATTERN 1 1 S see below (4839 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 | ------------------------------------------------------------------------------------------------------------------------------------ PA30-NW 1 WFC3/UVI ACCUM UVIS F673N 1 1 none none 1 810 S S PA30-NW 1 WFC3/UVI ACCUM UVIS F673N 1 2 none none 1 810 S S PA30-NW 1 WFC3/UVI ACCUM UVIS F673N 2 1 none none 1 810 S S PA30-NW 1 WFC3/UVI ACCUM UVIS F673N 2 2 none none 2 803 S S PA30-NW 1 WFC3/UVI ACCUM UVIS F673N 3 1 none none 2 803 S S PA30-NW 1 WFC3/UVI ACCUM UVIS F673N 3 2 none none 2 803 S S 18082( 5) - 04-Sep-2025 16:51:40 - [ 8] Visit: 04 (Pa30-NW-02) Visit Requirements: ORIENT 120D TO 290 D 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 PA30-NW WFC3/UVI ACCUM UVIS F673N FLASH=16.0 1 1160 S PATTERN 1 1 S see below (4839 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 | ------------------------------------------------------------------------------------------------------------------------------------ PA30-NW 1 WFC3/UVI ACCUM UVIS F673N 1 1 none none 1 810 S S PA30-NW 1 WFC3/UVI ACCUM UVIS F673N 1 2 none none 1 810 S S PA30-NW 1 WFC3/UVI ACCUM UVIS F673N 2 1 none none 1 810 S S PA30-NW 1 WFC3/UVI ACCUM UVIS F673N 2 2 none none 2 803 S S PA30-NW 1 WFC3/UVI ACCUM UVIS F673N 3 1 none none 2 803 S S PA30-NW 1 WFC3/UVI ACCUM UVIS F673N 3 2 none none 2 803 S S 18082( 5) - 04-Sep-2025 16:51:40 - [ 9] Visit: 05 (Pa30-SE-01) Visit Requirements: ORIENT 320D TO 9 D; ORIENT 66D TO 77 D; ORIENT 138D TO 155 D 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 PA30-SE WFC3/UVI ACCUM UVIS F673N FLASH=16.0 1 1160 S PATTERN 1 1 S see below (4839 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 | ------------------------------------------------------------------------------------------------------------------------------------ PA30-SE 1 WFC3/UVI ACCUM UVIS F673N 1 1 none none 1 810 S S PA30-SE 1 WFC3/UVI ACCUM UVIS F673N 1 2 none none 1 810 S S PA30-SE 1 WFC3/UVI ACCUM UVIS F673N 2 1 none none 1 810 S S PA30-SE 1 WFC3/UVI ACCUM UVIS F673N 2 2 none none 2 803 S S PA30-SE 1 WFC3/UVI ACCUM UVIS F673N 3 1 none none 2 803 S S PA30-SE 1 WFC3/UVI ACCUM UVIS F673N 3 2 none none 2 803 S S 18082( 5) - 04-Sep-2025 16:51:40 - [ 10] Visit: 06 (Pa30-SE-02) Visit Requirements: ORIENT 320D TO 9 D; ORIENT 66D TO 77 D; ORIENT 138D TO 155 D 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 PA30-SE WFC3/UVI ACCUM UVIS F673N FLASH=16.0 1 1160 S PATTERN 1 1 S see below (4839 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 | ------------------------------------------------------------------------------------------------------------------------------------ PA30-SE 1 WFC3/UVI ACCUM UVIS F673N 1 1 none none 1 810 S S PA30-SE 1 WFC3/UVI ACCUM UVIS F673N 1 2 none none 1 810 S S PA30-SE 1 WFC3/UVI ACCUM UVIS F673N 2 1 none none 1 810 S S PA30-SE 1 WFC3/UVI ACCUM UVIS F673N 2 2 none none 2 803 S S PA30-SE 1 WFC3/UVI ACCUM UVIS F673N 3 1 none none 2 803 S S PA30-SE 1 WFC3/UVI ACCUM UVIS F673N 3 2 none none 2 803 S S 18082( 5) - 04-Sep-2025 16:51:40 - [ 11] Visit: 07 (Pa30-SW-01) Visit Requirements: ORIENT 350D TO 240 D 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 PA30-SW WFC3/UVI ACCUM UVIS F673N FLASH=16.0 1 1160 S PATTERN 1 1 S see below (4839 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 | ------------------------------------------------------------------------------------------------------------------------------------ PA30-SW 1 WFC3/UVI ACCUM UVIS F673N 1 1 none none 1 810 S S PA30-SW 1 WFC3/UVI ACCUM UVIS F673N 1 2 none none 1 810 S S PA30-SW 1 WFC3/UVI ACCUM UVIS F673N 2 1 none none 1 810 S S PA30-SW 1 WFC3/UVI ACCUM UVIS F673N 2 2 none none 2 803 S S PA30-SW 1 WFC3/UVI ACCUM UVIS F673N 3 1 none none 2 803 S S PA30-SW 1 WFC3/UVI ACCUM UVIS F673N 3 2 none none 2 803 S S 18082( 5) - 04-Sep-2025 16:51:40 - [ 12] Visit: 08 (Pa30-SW-02) Visit Requirements: ORIENT 350D TO 240 D 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 PA30-SW WFC3/UVI ACCUM UVIS F673N FLASH=16.0 1 1160 S PATTERN 1 1 S see below (4839 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 | ------------------------------------------------------------------------------------------------------------------------------------ PA30-SW 1 WFC3/UVI ACCUM UVIS F673N 1 1 none none 1 810 S S PA30-SW 1 WFC3/UVI ACCUM UVIS F673N 1 2 none none 1 810 S S PA30-SW 1 WFC3/UVI ACCUM UVIS F673N 2 1 none none 1 810 S S PA30-SW 1 WFC3/UVI ACCUM UVIS F673N 2 2 none none 2 803 S S PA30-SW 1 WFC3/UVI ACCUM UVIS F673N 3 1 none none 2 803 S S PA30-SW 1 WFC3/UVI ACCUM UVIS F673N 3 2 none none 2 803 S S 18082( 5) - 04-Sep-2025 16:51:40 - [ 13] Summary Form for Proposal 18082 Item Used in this proposal ------------------------------------------------------------------------------------------------------------------------------------ Apertures UVIS ------------------------------------------------------------------------------------------------------------------------------------ Configurations WFC3/UVIS ------------------------------------------------------------------------------------------------------------------------------------ Opmodes ACCUM ------------------------------------------------------------------------------------------------------------------------------------ Optional Parameters FLASH=16.0 ------------------------------------------------------------------------------------------------------------------------------------ Special Requirements ORIENT 120D TO 290 D, ORIENT 138D TO 155 D, ORIENT 265D TO 272 D, ORIENT 292D TO 314 D, ORIENT 320D TO 9 D, ORIENT 324D TO 27 D, ORIENT 350D TO 240 D, ORIENT 37D TO 95 D, ORIENT 66D TO 77 D, PATTERN 1 1 ------------------------------------------------------------------------------------------------------------------------------------ Spectral Elements F673N ------------------------------------------------------------------------------------------------------------------------------------ Target Names PA30-NE, PA30-NW, PA30-SE, PA30-SW ------------------------------------------------------------------------------------------------------------------------------------