Asteroseismology of WD J004917.14-252556.81, the Most Massive Pulsating White Dwarf

Abstract

We present extensive follow-up time-series photometry of WD J0049$-$2525, the most massive pulsating white dwarf currently known with $T_{\mathrm{eff}}=13020\mathrm{K}$ and $\log g=9.34$ 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 $M_{\star }\approx 1.29M_{\odot }$, surface hydrogen layer mass of $\log (M_{\mathrm{H}}/M_{\star })\lesssim -7.5$, 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 d. This analysis provides the first look at the interior of a $\sim 1.3M_{\odot }$ white dwarf.

15 pages, 8 figures and 6 tables, accepted for publication in ApJ