LAMOST J101356.33+272410.7: A Detached White Dwarf–Main-sequence Binary with a Massive White Dwarf within the Period Gap

Abstract We report the analysis of the detached eclipsing spectroscopic binary system LAMOST J101356.33+272410.7, which features a massive white dwarf and has an orbital period of 185.82 minutes. Using Large Sky Area Multi-Object Fiber Spectroscopic Telescope and Sloan Digital Sky Survey spectra, we determined the stellar parameters, radial velocity semiamplitudes, and orbital periods of both components. Spectral energy distribution fitting of photometric data from the Galaxy Evolution Explorer, the Two Micron All Sky Survey, and Pan-STARRS1 yielded the effective temperatures and photometric radii. Eclipsing analysis of high-speed photometric data from the Liverpool Telescope provided orbital inclination, masses, radii, and related physical parameters. The white dwarf in this system has a mass of 1.05 ± 0.09 M ⊙ and a radius of 0.0090 ± 0.0008 R ⊙ , while the main-sequence star has a mass of 0.299 ± 0.045 M ⊙ and a radius of 0.286 ± 0.018 R ⊙ . Emission lines observed in the spectra indicate the likely presence of stellar magnetic activity in this system. The relatively cool temperature of the white dwarf suggests that the system could be a post-common-envelope binary (PCEB) that has not undergone mass transfer, while the presence of a massive white dwarf indicates that the system might also represent a detached cataclysmic variable crossing the period gap. We suggest that the system is more likely to be a PCEB, and it is predicted to evolve into a cataclysmic variable and begin mass transfer in approximately 0.27 Gyr.