Mean magnetic index ⟨ S_ph ⟩ identified by the star number given in Table 1. The stars are represented with different symbols according to their category in Table 2: L (red triangles), C (blue filled circle), T (pink squares), and O (open circles). KIC 3733735 is represented with the blue star since it belongs to both categories L and C. We superimposed the mean index of the Sun ⟨ S_ph, ⊙ ⟩  = 166.1 ± 2.6 ppm (dashed line), the index at low activity ⟨ S_ph(n_low) ⟩, (dot dash line), and the index at high activity ⟨ S_ph(n_high) ⟩ (triple dot dash line) obtained with the VIRGO data.