Filtering

With 167 images at 40.05 s cadence, the Nyquist frequency is 11.1 mHz and the frequency resolution is 0.13 mHz. After subtracting the mean this provides a range of detectable periodicity of 90-7692 s. A high-pass filter was employed such that all Fourier power below ~0.6 mHz (above ~1642 s in period space, corresponding to the maximum possible detectable period, see Section 6.3.4, Eqn. 6.3 and Figure 6.3) was removed. The importance of filtering is to increase the significance of the expected peak around 3-5 min by reducing aliasing effects. Filtering was carried out on each light curve by convolution with a suitable Bessel function so as to provide a smooth edge to the filter profile, and hence reduce ringing effects.