2025ApJ...988...32C

We present extensive follow-up time-series photometry of WD J0049-2525, the most massive pulsating white dwarf currently known, with T_eff = 13,020 K and ${\mathrm{log}}\,g=9.34$ cm s^–2. The discovery observations detected only two significant pulsation modes. Here, we report the detection of 13 significant pulsation modes ranging from 170 to 258 s based on 11 nights of observations with the New Technology Telescope, Gemini, and Apache Point Observatory telescopes. We use these 13 modes to perform asteroseismology and find that the best-fitting models (under the assumption of an ONe core composition) have M_⋆ ≈ 1.29M_⊙, a surface hydrogen layer mass of ${\mathrm{log}}\,({M}_{{\rm{H}}}/{M}_{\star })\lesssim -7.5$, and a crystallized core fraction of >99%. An analysis of the period spacing also strongly suggests a very high mass. The asteroseismic distance derived is in good agreement with the distance provided by Gaia. We also find tentative evidence of a rotation period of 0.3 or 0.67 days. This analysis provides the first look at the interior of a ∼1.3 M_⊙ white dwarf.