0 Assigned ID: 6689 ----- Attempting Submission 1 (Thu Apr 10 20:56:08 GMT 2025) ----- HST Phase I Proposal 6689 successfully submitted. Receipt: # 6689-1 Dear STSci, This resubmission includes the following adjustments: 1) slightly decreased increased dither spacing to ensure non-integer pixel dither seaparations 2) adoption of a 6-point dither, achieved with the WFC3-UVIS-MOS-DITH-LINE pattern, with 3 dithers in the main pattern, and 2 in the sub pattern. All dither spacings have been chosen to be 1.37 arcsec to ensure larger than chip gap, and non-integer in pixel scale. 3) The 6-point dither allows for 6 exposures per visit, chosen to improve image cleaning. Each exposure is now either 810 or 803 seconds to achieve 3 exposures per orbit. 4) increased post-flash to 16.0 electrons per pixel, as suggested by the ETC. 5) orient ranges have been approved by the TTRB (request 93327). We have made no changes to the orient ranges for this resubmission. Best wishes, Tim Cunningham 140105765 ----- Attempting Submission 1 (Tue Aug 12 00:56:37 GMT 2025) ----- HST Phase II Proposal 18082 successfully submitted. Receipt: # 18082-1 ----- Attempting Submission 2 (Wed Aug 13 19:50:50 GMT 2025) ----- HST Phase II Proposal 18082 successfully submitted. Receipt: # 18082-2 ----- Attempting Submission 3 (Thu Aug 14 20:16:47 GMT 2025) ----- ----- Attempting Submission 4 (Mon Sep 01 11:35:44 GMT 2025) ----- A Deeper Look at the Type Iax Supernova Remnant Pa 30 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. 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. 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. Dr. Tim Cunningham is an expert in the analysis of IFU spectroscopy and in the theoretical and observational studies of thermonuclear events. Dr. Ilaria Caiazzo is an expert in theoretical modeling and spectroscopic and photometric observations of white dwarfs and compact objects. She is the PI of two JWST proposals. Mr. Philippe Yao is an expert in photoionization modelling with Cloudy. Mr. Nikolaus Prusinki is an expert in the reduction and analysis of IFU spectroscopy. Prof. Jim Fuller is an expert in theoretical studies of stars and stellar remnants. Dr. Shrinivas Kulkarni is an expert in millisecond pulsars, brown dwarfs, soft gamma-ray repeaters, supernova remnants, gamma-ray bursts, new types of optical transients and instrumentation. Dr. Scott Kenyon uses observations and numerical simulations to study the formation of stars and planetary systems. Dr. John Raymond is an expert in spectroscopy, plasma physics and supernova remnants. Prof. Abigail Polin is an expert in theoretical studies of supernova remnants. Prof. Eliot Quataert is an expert in theoretical studies of black holes, stars, plasma astrophysics, and galaxy formation. Prof. Paul Duffell is an expert in theoretical studies of supernova remnants. Prof. Robert Fesen is an expert in observations and modeling of supernova remnants. Stellar Physics and Stellar Types Stellar Populations and the Interstellar Medium 6 false false false false false false false SUPPORTED ISM EMISSION LINE NEBULA SNR YES North-East (NE) quadrant of nebula (52 arcsec from central star; IRAS 00500+6713). IRAS-00500+6713-NE J2000 ISM EMISSION LINE NEBULA SNR YES North-West (NW) quadrant of nebula (52 arcsec from central star; IRAS 00500+6713). IRAS-00500+6713-NW J2000 ISM EMISSION LINE NEBULA SNR YES South-East (SE) quadrant of nebula (52 arcsec from central star; IRAS 00500+6713). IRAS-00500+6713-SE J2000 ISM EMISSION LINE NEBULA SNR YES South-West (SW) quadrant of nebula (52 arcsec from central star; IRAS 00500+6713). IRAS-00500+6713-SW J2000 WFC3/UVIS Imaging No No F673N POS-TARG MOSAIC DITHER 2 1.37 WFC3-UVIS-MOS-DITH-LINE false true 1.37 3 85.754 POS-TARG WFC3-UVIS-MOS-DITH-LINE 33.606 1 true The scheduling data was generated by CASM 33.1. 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