Solar-type stars MW and Tigre indices

Grading them (i.e., excellent, good, fair, and poor) and putting them into an evolutionary perspective, we find that stars more active than the Sun are also more likely to show cyclic variability than stars below solar activity. Furthermore, more active stars tend to have more regular cycles, while the solar mean S-value fits the lower end of the S-index range found for cyclic stars. This is consistent with the occurrence of solar Maunder minima episodes, hinting at a sometimes already unstable solar cycle.

We find eighteen stars with even lower activity and lower variability than the Sun, which provide a preview into the latter,s distant future. For half of these stars, we can use sensitive X-ray observations to complement our chromospheric data and to explore the lower end of stellar activity also from a coronal perspective. These so-called "Maunder minimum candidate stars" exhibit what we refer to as "remnant activity", which expresses itself in a minimal coronal flux and a minimal S-value, above which only rather small variations occur.

Using accurate Gaia DR3 distances allows us to place our sample stars into an Hertzsprung-Russell diagram (HRD), which demonstrates that active cyclic stars and inactive noncyclic stars populate rather different regions in the HRD.