Evolution of the Postmerger Remnants from the Coalescence of Oxygen–Neon and Carbon–Oxygen White Dwarf Pairs

Although multidimensional simulations have investigated the processes of double white dwarf (WD) mergers, postmerger evolution only focused on the carbon–oxygen (CO) or helium (He) WD merger remnants. In this work, we investigate for the first time the evolution of the remnants stemming from the merger of oxygen–neon (ONe) WDs with CO WDs. Our simulation results indicate that the merger remnants can evolve to hydrogen- and helium-deficient giants with a maximum radius of about 300 R⊙. Our models show evidence that merger remnants more massive than 1.95 M⊙ can ignite Ne before significant mass loss ensues, and they thus would become electron-capture supernovae. However, remnants with initial masses less than 1.90 M⊙ will experience further core contraction and longer evolutionary time before reaching the conditions for Ne burning. Therefore, their fates are more dependent on mass-loss rates due to stellar winds and thus more uncertain. Relatively high mass-loss rates would cause such remnants to end their lives as ONe WDs. Our evolutionary models can naturally explain the observational properties of the double WD merger remnant IRAS 00500+6713 (J005311). As previously suggested in the literature, we propose and justify that J005311 may be the remnant from the coalescence of an ONe WD and a CO WD. We deduce that the final outcome of J005311 would be a massive ONe WD rather than a supernova explosion. Our investigations may be able to provide possible constraints on the wind mass-loss properties of the giants that have CO-dominant envelopes.