Top panel: power spectrum of the photometric time series described in 2.2. As in Fig. 2, the thin grey and bold black lines represent the power spectrum smoothed with a 3.1-μHz wide triangular window, and a linearly increasing width triangular window, from 14 to 129 μHz across the [500, 4500] μHz frequency range, respectively. The spectrum is normalized such that its maximum value equals 1. The red dashed line indicates the background level fit. Bottom panel: échelle diagram of the power spectrum for a folding frequency of Δν₀ = 155 μHz, calculated in the same way as in Fig. 5.