tokens: et al. 2014 ). We used the same tools to produce periodograms for our SOAR and McDonald data, whose rapid acquisition cadence allowed us to identify the correct K2 periodogram alias (Figure 1 ). After identifying the true alias, we performed a least squares fit of a sinusoid to the K2 light curve data with the software Period04 (Lenz Breger 2014 ), using the peak frequency of 3152 μ Hz as an initial guess. Our best-fit value for the period of J1252 from K2 is 317.278 ± 0.013 s (3151.807 ± 0.013 μ Hz). When fitting to the ground-based data, we used this period as an initial guess, and performed nonlinear least squares fits to determine if the period was consistent for all data sets (Table 2 ). Table 2 Results of Nonlinear Least Squares Fits of a Sinusoidal Signal to McDonald Observatory Light Curves from 2018 to 2019 Note. The equation used is , where the initial guess for P is the period determined from the K2 data (317.278 ± 0.013 s). We report the time of first photometric maximum in each filter for each set as determined from the phase term. Because white dwarf rotation rates are typically on the order of hours to days (Berger et al. 2005 ; Hermes et al. 2017b ), we were surprised to find that the period of this object was far shorter, falling at over 11 times the Kepler long-cadence Nyquist frequency (283.5 μ Hz). Murphy ( 2014 ) presents the function by which periodogram amplitude diminishes with super-Nyquist signals as , where t exp is the instrument sampling rate, and P is the object period. For J1252, the measured amplitude from the Kepler long-cadence sampling rate is diminished by a factor of 17.79 compared to the intrinsic. The inferred intrinsic amplitude from this is 4.20%, which is comparable to the 4.56% amplitude from the McDonald BG40 data (Figure 1 ). The remaining difference is attributable to the respective Kepler and BG40 filter bandpass shapes and wavelength ranges. We detected a significant difference in color amplitude, with ratio g / i = 2.26 ± 0.22 in our multicolor light curves, but did not detect a significant phase shift between the two colors (Figure 2 ). The individual fits also show evidence of period and phase modulations. The 2018 McDonald BG40 and SDSS filter sets were separated in acquisition by one day, but show a 2–3 σ difference in the object period. In addition, there is significant power asymmetry in the lobes of the primary feature of the Fourier transform for the observational data, indicative of phase modulation. More data are needed to explore these phenomena further. Figure 2. Folded light curves of J1252 in SDSS- g and - i filters from McDonald Observatory in 2018. We note a large ratio (>2) in amplitude between the two filters, and no apparent phase difference. 3.2. Atmospheric Parameters and Magnetism We present the phase-binned 400 l mm −1 SOAR spectra of J1252 in Figure 3 . To produce these, we folded our individual spectra into five equally spaced phase bins, each covering one-fifth of the
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