Filtering of the same image at three different frequencies. Downflows are represented in blue, upflows in red tones. A) Selected zone of the star. B) and C) frequency spectra of points B) and C) where we see one or two main peaks. The vertical axis represents the normalized radial velocity. The vertical red line indicates the position of the Gaussian filter (width = 2 × 10^-4 mHz). D1), D2) and D3): result of the filtering of image A) at three frequencies. Wave beams are visible with an inclination that varies with the frequency, forming St Andrew’s crosses. The angles’ values are indicated in Table 1.