A White Dwarf–Main-sequence Binary Unveiled by Time-domain Observations from LAMOST and TESS

• Published in: The Astrophysical journal 2022-09, Vol.936 (1), p.33
• Main Authors: Zheng, Ling-Lin, Gu, Wei-Min, Sun, Mouyuan, Zhang, Zhi-Xiang, Yi, Tuan, Wu, Jianfeng, Wang, Junfeng, Fu, Jin-Bo, Qi, Sen-Yu, Yang, Fan, Wang, Song, Wang, Liang, Bai, Zhong-Rui, Zhang, Haotong, Li, Chun-Qian, Shi, Jian-Rong, Zong, Weikai, Bai, Yu, Liu, Jifeng
• Format: Article
• Language: English
• Subjects: Astrophysics; Close binary stars; Companion stars; Extrasolar planets; Galactic evolution; Galaxies; Inclination angle; Light curve; Light curves; Main sequence stars; Orbits; Planet detection; Polls & surveys; Radial velocity; Sky surveys (astronomy); Spectral energy distribution; Spectroscopic telescopes; Spectroscopy; Time domain analysis; Transit; White dwarf stars
• ISSN: 0004-637X; 1538-4357
• DOI: 10.3847/1538-4357/ac853f

We report a single-lined white dwarf–main-sequence binary system, LAMOST J172900.17+652952.8, which is discovered by the Large Sky Area Multi-Object Fibre Spectroscopic Telescope (LAMOST)’s medium-resolution time-domain surveys. The radial-velocity semi-amplitude and orbital period of the optical visible star are measured by using follow-up observations with the Palomar 200 inch telescope and light curves from the Transiting Exoplanet Survey Satellite (TESS). Thus the mass function of the invisible candidate white dwarf is derived, f ( M 2 ) = 0.120 ± 0.003 M ⊙ . The mass of the visible star is measured based on a spectral energy distribution fitting, M 1 = 0.81 − 0.06 + 0.07 M ⊙ . Hence, the mass of its invisible companion is M 2 ≳ 0.63 M ⊙ . The companion ought to be a compact object rather than a main-sequence star owing to the mass ratio q = M 2 / M 1 ≳ 0.78 and the single-lined spectra. The compact object is likely to be a white dwarf if the inclination angle is not small, i ≳ 40°. By using the Galaxy Evolution Explorer (GALEX) near-UV flux, the effective temperature of the white dwarf candidate is constrained as T eff WD ≲ 12,000–13,500 K. It is difficult to detect white dwarfs which are outshone by their bright companions via single-epoch optical spectroscopic surveys. Therefore, optical time-domain surveys can play an important role in unveiling invisible white dwarfs and other compact objects in binaries.