BLS spectrum of the TFA-filtered/reconstructed time series based on the observations of WASP-33 by HATNet. The label in the upper right corner shows, from left to right, the pre-whitening order, peak frequency, transit depth (assuming trapezoidal transit shape) and the S/N of the peak frequency. The BLS amplitude is normalized to unity at the highest peak and refers to the signal without correction for blending by the nearby companion (see text).