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Fig. 2


Variations of SCa   II, Hα   , Na   i and He   i with time for the 12 stars with long-term variability (see Sect. 4). For visualization purposes, the y-axis is defined as the mean of the data plus and minus 0.35 times the maximum of the average errors of each index. The x-axis is constant for all stars. Note that Gl877 does not have data for the SCa   II index.

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