2023MNRAS.523.1591G

Tsinghua University-Ma Huateng Telescope for Survey (TMTS) aims to discover rapidly evolving transients by monitoring the northern sky. The TMTS catalogue is cross-matched with the white dwarf (WD) catalogue of Gaia EDR3, and light curves of more than a thousand WD candidates are obtained so far. Among them, the WD TMTS J23450729+5813146 is one interesting common source. Based on the light curves from the TMTS and follow-up photometric observations, periods of 967.113, 973.734, 881.525, 843.458, 806.916, and 678.273 s are identified. In addition, the TESS observations suggest a 3.39-h period but this can be attributed to the rotation of a comoving M dwarf located within 3 arcsec. The spectroscopic observation indicates that this WD is DA type with T_eff = 11 778 ± 617 K, log g = 8.38 ± 0.31, mass = 0.84 ± 0.20 M_⊙, and age = 0.704 ± 0.377 Gyr. Asteroseismological analysis reveals a global best-fitting solution of T_eff = 12 110 ± 10 K and mass = 0.760 ± 0.005 M_⊙, consistent with the spectral fitting results, and oxygen and carbon abundances in the core centre are 0.73 and 0.27, respectively. The distance derived from the intrinsic luminosity given by asteroseismology is 93 parsec, which is in agreement with the distance of 98 parsec from Gaia DR3. Additionally, kinematic study shows that this WD is likely a thick-disc star. The mass of its zero-age main sequence is estimated to be 3.08 M_⊙ and has a main sequence plus cooling age of roughly 900 Myr.