Asteroseismology of the ultramassive ZZ ceti star WDÂ 0246+326

The internal structures of pulsating white dwarfs can be explored only with asteroseismology. Time series photometric observations were made for the pulsating DA white dwarf (ZZ Ceti star) WD 0246+326 during 9 nights in 2014 with a bi-site observation campaign. Eleven frequencies were detected including 1 triplet, 2 doublets, and 4 single modes, which are identified as either l=1 or l=2 modes with the complementarity of frequencies present in the literature. From the multiplets, the rotation period of WD 0246+326 is derived as 3.78 ± 0.11 days. The average period spacing of the l=1 modes ΔP=29.3±0.2 s, implies that WD 0246+326 may be a massive ZZ Ceti star concerning the ΔP−M* relationship for the DAVs. Preliminary analysis derives the stellar parameters of M*=0.98±0.01M⊙ and Teff=11700±100 K by fitting the theoretical frequencies of the eigen modes to the observed ones.