Illustration of how the shape and features of the period histogram in Fig. 5 would evolve when varying the bin size (upper panels) or the bin phase (lower panels). The starting bin size and phase (of 1 d and 0, respectively; these are shown on the upper left panel and on the lower left panel of this figure) correspond to those adopted in Fig. 5 and considered for the subsequent analysis. In the upper panel, the bin size is progressively increased by 0.25 d at each step from the left diagram to the right diagram; in the lower panel, a fixed bin size of 1 d is adopted and the bin center is progressively shifted by 0.2 d at each step from the left diagram to the right diagram.