Periodograms from HD 123351 photometry. a) Discrete Fourier transform (DFT) periodogram from the pre-whitened V-band data (top panel). The twelve-year average period is 61.9 d (0.01616 c/d). The bottom panel is the corresponding window function. The insert in the top panel shows the entire search range. b) Two-dimensional short-term Fourier transform (STFT) analysis. The power distribution in the time-frequency plane is shown as a gray scale (black means highest power, white no power). It shows that the photometric period reached values between a maximum of 62.0 d and a minimum of 57.3 d. Around 2 453 000 (2002–2005), a bimodal distribution was recovered. Note that the excess power in the lower left corner is due to the length of the data vector and is artificial.