Flux in the Hα line for different levels of activity. Upper panels: Hα line profiles of HD 215152 (left), HD 20003 (middle), and HD 7199 (right) at their maxima (red) and minima (blue) activity levels. Lower panels: difference between the fluxes at the maximum and minimum of activity for each star. Vertical lines show bandwidths of 2.0 Å (solid), 1.6 Å (dashed), and 0.6 Å (dotted). The numbers in the lower panels show the integrated flux difference in each region delimited by the vertical lines in red if positive and blue if negative.