Mapping the distribution of accreted metals on the surface of WD G29-38 with TESS and HST

White dwarf (WD) star G29-38 exhibits large-amplitude g-mode pulsations with frequencies ranging from 500 to 4000 μHz. Classified as a DAVZ (hydrogen dominated atmosphere, variable, with atmospheric metals present), it also shows an infrared excess attributed to a circumstellar dust disk. The presence of metals indicates ongoing accretion. The goal of this work is to use the pulsations to constrain the geometry of metal accretion on the surface of G29-38, e.g., polar versus equatorial. Using time-series photometric data from TESS and overlapping time-series spectral data from HST, we can tie its photometric variations to abundance variations derived from the time-series spectra. Next, using non-linear lightcurve fitting techniques (Montgomery 2005; Montgomery et al. 2010), we can use the non-linearities in the light curve to constrain the temperature and flux variations on its surface. The "hot spots" that occasionally appear due to pulsations will dominate the spectra, so the abundances determined from the spectra at these times will constrain the atmospheric abundances at the location of the "hot spots". We employ advanced Fourier transform techniques to track amplitude variations in the pulsation modes. While straightforward in principle, we find that G29-38 shows such significant amplitude variations in many of its modes that a determination of the pulsation amplitudes at the precise times that the HST spectra were taken is a critical part of the analysis.