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Fig. 5

image

Example of a cycle period categorised as CA (HD 81809). The top plot shows the data in black, and the red curve shows the fit to the strongest peak in the periodogram shown in the bottom plot. The shaded grey area shows the span of the solar chromospheric activity from one minimum to the maximum shifted to the centre at the star’s mean value. The dashed horizontal line shows the mean of the data points. The strongest frequency is marked by the dashed red line in the bottom plot.

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