Figure 6: Relation between the periodic photometric variability amplitude and the S index.
From: Observational evidence for enhanced magnetic activity of superflare stars
The periodic photometric variability amplitudes are from McQuillan et al.36 for 1,400 stars that also have LAMOST spectra that allow reliable measurements of the chromospheric emission. Indication of a correlation is seen down to periodic photometric variability amplitudes around 1,000 p.p.m., which is the level of the amplitudes seen in the Sun. Below 1,000 p.p.m. no clear indication of a correlation is seen, indicating that the relation between spot coverage and chromospheric emission breaks down when the magnetic activity is low.
