Activity indexes time series and periodograms. Left: activity indexes (defined in the text) as a function of time. Daily median values are shown. Centre: zoom on the time series covering a period of two rotations. Right: corresponding generalised Lomb-Scargle periodograms (after the subtraction of the main long-term periods, see text for details). The light blue lines indicate the solar synodic period of 27.2753 days (Allen 1977) while values corresponding to a FAP of 10%, 1%, and 0.1% are shown with dashed lines.