  Tsinghua university-Ma Huateng Telescope for Survey (TMTS) aims to discover
rapidly evolving transients by monitoring the northern sky. The TMTS catalog is
cross-matched with the white dwarf (WD) catalog of Gaia EDR3, and light curves
of more than a thousand WD candidates are obtained so far. Among them, the WD
TMTS J23450729+5813146 (hereafter J2345) is one interesting common source.
Based on the light curves from the TMTS and follow-up photometric observations,
periods of 967.113 s, 973.734 s, 881.525 s, 843.458 s, 806.916 s 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".
The spectroscopic observation indicates that this WD is DA type with Teff =
11778+/-617K,log g = 8.38+/-0.31,mass=0.84+/-0.20Msun and age=0.704+/-0.377
Gyrs. Asteroseismological analysis reveals a global best-fit solution of Teff
=12110+/-10K and mass=0.760+/-0.005Msun,consistent with the spectral fitting
results, and Oxygen and Carbon abundances in the core center 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 disk star. The mass of its zero-age main-sequence mass is
estimated to be 3.08 Msun and has a main-sequence plus cooling age of roughly
900 Myrs.
