Variable white dwarfs in TMTS: asteroseismological analysis of a ZZ Ceti star, TMTS J17184064+2524314

ABSTRACT The Tsinghua University-Ma Huateng Telescope for Survey (TMTS) has been constantly monitoring the northern sky since 2020 in search of rapidly variable stars. To find variable white dwarfs (WDs), the TMTS catalogue is cross-matched with the WD catalogue of Gaia EDR3, resulting in over 3000 light curves of WD candidates. The WD TMTS J17184064+2524314 (hereafter J1718) is the second ZZ Ceti star discovered among these common sources. Based on the light curves from TMTS, follow-up photometric observations, and Transiting Exoplanet Survey Satellite, 10 periods and three combination periods are detected. A rotation period of 25.12 ± 0.18 h is derived, according to the identified rotational splitting. Our spectroscopic observation indicates that this WD belongs to DA type with Teff = 11 670 ± 604 K, log g = 8.16 ± 0.36, M = 0.70 ± 0.23 M⊙, and age = 0.51 ± 0.34 Gyr. Based on core-parametrized asteroseismological model grids (≥14 million), we derive the best-fitting solution of Teff = 11 640 ± 20 K, log g = 8.267 ± 0.008, and M = 0.750 ± 0.005 M⊙ for J1718, consistent with the spectral fitting results. For this WD, the corresponding carbon and oxygen abundances in the core are 0.43 and 0.57, respectively. The distance derived from the intrinsic luminosity given by asteroseismology is 64 ± 15 pc, in accord with the distance of 70.1 ± 0.2 pc from Gaia DR3 within the uncertainties.