Power spectra of simulated white noise (top) and red noise time series (bottom) with the period range 2.4−2.8 d. a): LS periodogram of the average of 5000 simulated white noise time series; b): integrated WWZ power spectrum of 5000 simulated white noise time series; c): WWZ power spectrum of the average of 5000 simulated white noise time series; d): LS periodogram of the average of 5000 simulated red noise time series; e): integrated WWZ power spectrum of 5000 simulated red noise time series; f): WWZ power spectrum of the average of 5000 simulated red noise time series.