FTs of the observed light curve of BPM 37093 from multisite WET campaigns in (a) 1998 and (b) 1999, along with (c) single‐site observations from Magellan in 2003. Each panel also contains the corresponding window function—the pattern of alias peaks present in the Fourier Transform for each real frequency. The amplitudes of various pulsation modes change over time, but their frequencies are stable.