Chromospheric index derived from the Hermes observations and calibrated into the MWO system as a function of the photospheric S_ph (in ppm) of the seismic solar analogs observed with the Kepler satellite. The corresponding activity levels of the Sun at minimum and maximum of its 11-yr magnetic cycle are represented by the horizontal and vertical dashed lines. The size of the symbols is inversely proportional to the rotation period. Each star is referred by the same number as given in Tables 2 and 3.