Index of chromospheric emission S_CaII as a function of photometric modulation S_ph (in log scale). Upper panel: results for 3130 red giant stars observed by both LAMOST and Kepler, from the Gaulme et al. (2020) catalog. Gray symbols refer to regular inactive red giants (i.e., with no evidence of spot modulation) that display oscillations, while the other colors refer to photometrically active giants (i.e., exhibiting spot modulation): blue symbols refer to red giants with partially suppressed oscillations; black symbols refer to non-oscillating red giants in close binary systems; and green symbols refer to non-oscillating red giants with ambiguous binary versus single status. The gray line represents the best linear fit given by Eq. (5). Values of S_ph are from Gaulme et al. (2020). Bottom panel: zoom on the upper panel for inactive red giants, with the x-axis in linear scale.