0 Assigned ID: 5989 ----- Attempting Submission 1 (Thu Nov 07 22:13:54 GMT 2024) ----- HST Phase I Proposal 5989 successfully submitted. Receipt: # 5989-1 ----- Attempting Submission 2 (Thu Nov 07 22:58:36 GMT 2024) ----- 0 ----- Attempting Submission 1 (Wed Jan 22 00:46:35 GMT 2025) ----- One Last Time: HST/ACS Imaging of the Peculiar White Dwarf Supernova 2012Z Type Ia supernovae (SNe Ia) play a central role in cosmology, stellar evolution, and cosmic chemical enrichment. Nonetheless, their progenitors and explosion mechanisms remain uncertain. The classic model -- a Chandrasekhar-mass white dwarf (WD) accreting mass from a non-degenerate companion -- may not explain normal SNe Ia, but aligns well with observations of the peculiar Type Iax supernova (SN Iax) subclass. Intriguingly, pure deflagration (subsonic) explosion models of SNe Iax predict that the WD may not be completely disrupted, potentially leaving behind a bound remnant. SN Iax 2012Z offers an exceptional opportunity to stringently test this scenario. Deep pre-explosion HST ACS/WFC imaging of its host galaxy, NGC 1309, revealed a luminous, blue helium star thought to be the companion of the exploding WD. Subsequent ACS/WFC imaging at the location of SN 2012Z in 2016 and 2019 revealed that, remarkably, this source is still visible with a persistent flux excess beyond that expected from the companion star alone. We propose one final ACS/WFC observation, six years after the last, allowing for image subtraction to conclusively determine whether this mysterious flux excess originates from a bound remnant driving a radioactive wind or from shock-heating of the ejecta-blasted companion star. This observation will cement the legacy of HST in elucidating the origins of SNe Iax. We propose to obtain late-time optical ACS/WFC BVI images at the location of SN 2012Z in NGC 1309 to look for further changes in the system. We have constructed our proposed observations to match the ACS/WFC data from Cycles 22 and 25 in filters and depth, allowing us to also compare with the pre-explosion ACS images and photometry of S1. Our best measurement of any changes from the pre-explosion and Cycle 22 or 25 images will come from image-subtraction analysis, so we request a similar orientation range as those data. We will use dithering and subsampling to improve the spatial resolution of the ACS images, as we did in our previous observations, and thus request the same orientation for all visits. We divide our 14-orbit allocation into 5 visits, 4 visits of 3 orbits each in all three filters (F435W, F555W, and F814W) and 1 visit of 2 orbits in two filters (F555W and F814W). This yields a total exposure time of over 9000 sec in F435W and approximately 11500 sec in F555W and F814W. PI Schwab is leading the analysis of existing HST data on this source. CoI Jha is an expert on white dwarf supernovae and on SN 2012Z especially and will serve as Admin PI and the primary research advisor to Schwab. CoI McCully led the analysis of previous HST imaging of this source and has published this work. CoIs Foley, Graur, Kwok, Larison, and Sears have extensive experience with HST analysis and studies of white dwarf supernovae and will serve as mentors to PI Schwab. Stellar Physics and Stellar Types 6 false false false false false false SUPPORTED EXT-STAR SUPERNOVA J2000 J2000 ACS/WFC Imaging No No F435W ACS/WFC Imaging No No F555W ACS/WFC Imaging No No F814W Hst Same orient constraint links visits (01 02 03 04 05) The scheduling data was generated by CASM 33.0. 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