In a recent study published in The Astrophysical Journal Letters, a research group led by assistant professor WU Chengyuan from Yunnan Observatories, Chinese Academy of Sciences (CAS) investigated the evolution of postmerger remnants from the coalescence of oxygen-neon white dwarf (WD) and carbon-oxygen WD. Researchers found that the evolutionary outcomes of such remnants are related to their total masses, and they used the corresponding models to explain the oxygen-rich object IRAS 00500+6713 (J005311) located in the infrared nebula in Cassiopeia.

Double WDs in binary systems can merger together due to the gravitational wave radiation. Double WD binaries are important gravitational wave sources in our Galaxy, and the mass of which are related to the type Ia supernovae, electron capture supernovae and millisecond pulsars. Thus it is very important to investigate double WD mergers.

At present, the evolutionary outcomes of the mergers of oxygen-neon WD and carbon-oxygen WD are still unclear. WU constructed the corresponding models to investigate their evolution. Researchers found that such merger remnants can evolve to carbon-oxygen giants, and their evolutionary outcomes are related to their total masses. Under the fixed wind mass-loss prescription, remnants with masses lighter than 1.90M_⊙ can evolve to oxygen-neon WDs, whereas the remnants with masses greater than 1.95M_⊙ can experience electron capture supernova explosions to become oxygen-neon-iron WDs.

This result implies that the super-Chandrasekhar mass remnants which are originated from the mergers of oxygen-neon WD and carbon-oxygen WD cannot form neutron stars, which challenged the traditional understandings.

Recent years, researchers found a new hot star IRAS 00500+6713 (J005311) located in the infrared nebula in Cassiopeia. The spectrum of this object is similar to that of the oxygen-rich Wolf-Rayet stars, and it has relatively high wind mass-loss rate and extremely high wind velocity. At present, the origin of this object is still unclear. WU explained the observational features of this object by using their models successfully, and found that this object is originated from the merger of a 1.08M_⊙ oxygen-neon WD with a 0.52M_⊙ carbon-oxygen WD. This work improves our understanding of the super-Chandrasekhar mass double WD merger remnants and the relative objects.

Contact:
WU Chengyuan
Yunnan Observatories, CAS
E-mail: wuchengyuan@ynao.ac.cn