IRAS 00500+6713: SN 1181 Remnant

• IRAS 00500+6713 is a rare, hot stellar remnant from a double white dwarf merger with extreme wind properties and unique spectral signatures.
• Its surrounding nebula exhibits stratified infrared, optical, and X-ray emissions that align with the historical SN 1181 event and reveal complex ejecta dynamics.
• Detailed spectroscopy uncovers advanced nucleosynthetic products and significant mass loss, offering critical insights into the evolution of Type Iax supernova remnants.

IRAS 00500+6713 is a hot, hydrogen- and helium-deficient stellar remnant embedded in a nebula exhibiting both infrared and X-ray emission. Identified as the product of a double-degenerate white dwarf merger with physical properties and historical context linking it to the supernova SN 1181, IRAS 00500+6713 (also known as Pa 30 and WD J005311) is the only confirmed bound remnant of a Type Iax supernova in the Galaxy.

1. Identification, Discovery, and Historical Context

IRAS 00500+6713 was first detected as a diffuse mid-infrared nebulosity (Pa 30) in WISE data by Patchick in 2013, initially classified as a planetary nebula candidate (Ritter et al., 2023). Advanced spectroscopic studies demonstrated its central star’s peculiar properties that do not match typical planetary nebula nuclei, quickly linking the object to a double white dwarf (WD) merger and a rare Type Iax supernova. Historical Chinese, Japanese, and more recently Arabic records describe a bright, long-lived transient in Cassiopeia in 1181 AD, with properties—including approximate position and brightness (~2.2 mag, brighter than α Cas)—consistent with the location and age of IRAS 00500+6713 and its nebula (Fischer et al., 4 Sep 2025). The expansion age of the nebula, derived from $t_{\rm exp} = R/v_{\rm exp}$, is about $990^{+280}_{-220}$ years, directly matching the explosion epoch.

2. Central Star Properties and Spectroscopy

The central star of IRAS 00500+6713, WD J005311 (or "Parker's star"), is classified spectroscopically as a Wolf-Rayet of the WO subtype, uniquely originating from a WD merger rather than a massive star (Oskinova et al., 2020, Ritter et al., 2023). Key parameters:

• Effective Temperature: $T_{*} \approx 211{,}000 - 280{,}000$ K
• Luminosity: $\log_{10}(L_{*}/L_{\odot}) \approx 4.6$ ($L_{*} \sim 4 \times 10^{4}~L_{\odot}$)
• Wind Terminal Velocity: $$v_{\infty} \sim 16{,}000~\mathrm{km\,s}^{-1}\ (\sim 0.05c)$$
• Mass-Loss Rate: $$\dot{M} \sim 3.5 \times 10^{-6}\ M_{\odot}\,\mathrm{yr}^{-1}$$
• Atmospheric Abundances: Dominated by oxygen and carbon, with mass fractions $X_{\rm O} \sim 0.8$, $X_{\rm C} \sim 0.2$, virtually no hydrogen or helium, and unusually high silicon and sulfur.

The wind composition and broad, highly ionized emission lines (O VI–VIII, C IV–VI) identify advanced carbon burning ashes. The absence of a massive-star progenitor or classical PN context is unprecedented.

3. Nebula Morphology, Multi-wavelength Structure, and Expansion

The nebula of IRAS 00500+6713 displays a complex, stratified profile (Ko et al., 2023):

• Infrared: A prominent dusty ring seen at $22\,\mu$m (WISE data), interpreted as unshocked SN ejecta or a dust sublimation front.
• X-ray: Two distinct regions—a compact central (wind termination shock; radius $0.009{-}0.018$ pc) and a diffuse outer nebula (forward shock in SN ejecta–ISM interface; radius $1.46$ pc, angular radius $\sim 131''$).
• Optical: [O III], [S II] emission lines, with nebular radial velocities $$v_{\mathrm{rad}} \sim 1,100 \pm 100~\mathrm{km\,s}^{-1}$$, matching the expected expansion from a 1181 AD event.

The total nebular mass in hot gas ($\sim 0.1~M_{\odot}$, mainly C, O, Ne, Mg) and plasma temperatures $1{-}20$ MK complement the remnant’s energetic output.

4. Double-degenerate Merger and SN Iax Event

Current consensus interprets IRAS 00500+6713 as the bound remnant of a merger between an oxygen–neon–magnesium (ONeMg) WD and a carbon–oxygen (CO) WD (Oskinova et al., 2020, Wu et al., 2023, Ko et al., 2023). The less massive CO WD was tidally disrupted, forming a disk around the ONe WD and igniting carbon burning. The object’s present mass ($M_{\rm tot} \sim 1.5~M_{\odot}$, potentially decreasing under strong wind mass loss) was super-Chandrasekhar post-merger.

The merger was accompanied by a low-energy Type Iax SN (energy $E_{\rm ej} = 0.77{-}1.1 \times 10^{48}$ erg, $M_{\rm ej} = 0.18{-}0.53~M_{\odot}$), ejecting intermediate-mass elements (notably Si and S) and leaving the current remnant (Ko et al., 2023). The timing of intense wind onset ($\sim$1990 AD, $\sim$810–828 yr after explosion) is likely linked to Kelvin-Helmholtz contraction and the initiation of surface carbon burning.

5. Observational Diagnostic Features and Photoinization Modeling

The nebula’s observational signatures substantially differ from typical planetary nebulae (Yao et al., 2023):

• Photoionization Simulations (CLOUDY): Revealed weak hydrogen lines (H$\alpha$, H$\beta$) and strong carbon/oxygen recombination and fine-structure lines (e.g., C IV 7727 Å, [O IV] 25.9 μm).
• Line Ratios: $F_{\mathrm{WD}}/F_{\mathrm{PN}} \sim 35$ for C IV 7727 Å; Ne VI and Mg VII predicted to be detectable by JWST.
• Dust Reprocessing: Models including $\sim$10% graphite/silicate by mass show mid-IR flux dominated by dust continuum, not fine-structure lines (WISE bands), but JWST will resolve diagnostic lines.

This set of features distinguishes WD merger remnants from classical novae or PNe and is the most powerful signature for recognizing objects like IRAS 00500+6713.

6. Post-merger Evolution and Fate

The future trajectory of IRAS 00500+6713 is modulated by mass-loss rate and core contraction (Oskinova et al., 2020, Wu et al., 2023):

• Current State: Remnant above the Chandrasekhar limit, extreme wind ablation.
• Low-mass regime ($M_{\rm tot} < 1.90~M_{\odot}$): Extended core growth, wind erodes CO-rich layers, likely fate—a massive ONe WD.
• High-mass regime ($M_{\rm tot} > 1.95~M_{\odot}$): Rapid neon burning or electron-capture supernova (ECSN), core collapse to neutron star.
• Wind Prescription Sensitivity: Efficient wind (e.g., Blocker’s with $\eta_B=0.05$, rates $\sim 10^{-4}~M_{\odot}$ yr$^{-1}$) crucial to matching observed properties and dictating final outcome.

Electron captures (particularly on $^{24}$Mg) at high core density prompt loss of degeneracy support, eventual collapse follows $\rho$ and $P \propto \rho^{5/3}$ until critical electron capture threshold reached.

7. Scientific Impact and Context within Supernova Studies

IRAS 00500+6713 serves as a pivotal probe at the intersection of close binary evolution, thermonuclear supernova theory, and nucleosynthesis (Oskinova et al., 2020, Ritter et al., 2023). Its unique combination of extreme stellar wind, post-merger chemistry (high Si, S), complex nebular kinematics, and direct historical linkage to SN 1181 enables:

• Direct empirical connection between double-degenerate white dwarf mergers and Type Iax SNe.
• Calibration point for photoionization and hydrodynamic models of low-energy SN remnants.
• Constraints on wind mass-loss rates of hydrogen-, helium-deficient giants with CO-dominant envelopes.
• Insight into nucleosynthetic processes of incomplete C/O burning, as traced by Mg, Ne, Si, S enrichment.
• Benchmarking for the paper of bound SN remnants and diversity of outcomes in binary compact object evolution.

This object provides a “Rosetta Stone” for interpreting SN Iax events and validating historical astronomical records with modern astrophysical data (Ritter et al., 2023, Fischer et al., 4 Sep 2025).