Lomb-Scargle periodograms, each of them normalized to its maximum power, for subsectors of sector A (left panels), B (middle panels), and C (right panels) after the filtering-out of the instrumental periodicity of 13 min, computed at radial distances of 1.8, 2.0, 2.2, and 2.4 R_⊙ as reported at the right side of each panel. The peaks at 42 min are highlighted by a light yellow shaded area. The 95% and 99% confidence levels are reported as solid yellow and red lines, respectively.