A New Study on a Type Iax Stellar Remnant and its Probable Association with SN 1181

We report observations and modeling of the stellar remnant and presumed double-degenerate merger of Type Iax supernova Pa 30, which is the probable remnant of SN 1181 AD. It is the only known bound stellar SN remnant and the only star with Wolf-Rayet features that is neither a planetary nebula central star nor a massive Population I progenitor. We model the unique emission-line spectrum with broad, strong O VI and O VIII lines as a fast stellar wind and shocked, hot gas. Non-LTE wind modeling indicates a mass-loss rate of ~10<SUP>-6</SUP> M <SUB>⊙</SUB> yr<SUP>-1</SUP> and a terminal velocity of ~15,000 km s<SUP>-1</SUP>, consistent with earlier results. O VIII lines indicate shocked gas temperatures of T ≃ 4 MK. We derive a magnetic field upper limit of B &lt; 2.5 MG, below earlier suggestions. The luminosity indicates a remnant mass of 1.0-1.65 M <SUB>⊙</SUB> with ejecta mass 0.15 ± 0.05 M <SUB>⊙</SUB>. Archival photometry suggests the stellar remnant has dimmed by ~0.5 mag over 100 yr. A low Ne/O &lt; 0.15 argues against an O-Ne white dwarf in the merger. A cold dust shell is only the second detection of dust in an SN Iax and the first of cold dust. Our ejecta mass and kinetic energy estimates of the remnant are consistent with Type Iax extragalactic sources.