Lomb-Scargle periodograms of TESS data, after splitting the data into four equal segments of approximately 13 days each (BJD ranges are denoted in the figure legend). Each row shows one of the four strongest harmonics of the 23.07 min signal. Note that the axis range in each panel has been scaled by the harmonic number, so that a consistent offset in the figure represents a consistent fractional change in frequency between different harmonics. The vertical dashed line shows the 23.07 min signal derived from the combined periodogram of the entire TESS light curve and its harmonics. The periodic signal appears to be constant through the first three segments, while it appears to drift towards a slightly lower frequency during the final segment.