A Seismic Technique for Obtaining White Dwarf Fundamental Parameters from Mean Period Spacings and Astrometry

Abstract

We present a new statistical technique that utilizes the synergy of precision astrometry and time series photometry from modern space missions to obtain reliable physical parameters of pulsating white dwarf stars. We compute a grid of white dwarf structural models that span the helium-atmosphere pulsating white dwarf (DBV) instability strip, showing that mean period spacings between adjacent pulsation modes and absolute magnitudes derived from Gaia astrometry vary monotonically and in opposing directions across parameter space. While most efforts in white dwarf asteroseismology to directly fit individual pulsation periods to stellar models result in degenerate and poorly resolved solutions, the "seismic technique" produces unique and reliable seismic solutions for global parameters of mass and effective temperature when a reliable mean period spacing is detected. Our models sample various physically plausible interior chemical composition profiles based on modern evolutionary models to propagate uncertainty from the precise structures of actual stars. Once the global stellar parameters are tightly constrained, seismically resolving white dwarf interior structures becomes more computationally tractable, and degeneracies can be resolved. This new seismic technique is largely insensitive to the precise absorption line profiles interpreted by the widely used spectroscopic technique, and therefore provides complementary constraints that can be used to test spectroscopic methods. We demonstrate the method for the pulsating helium-atmosphere white dwarf WD 0158-160 observed by TESS, obtaining $T_\mathrm{eff} = 24584\pm 971$ K and $M_\star = 0.608\pm 0.013$ $M_\odot$.