The connection between starspots and superflares: a case study of two stars

Abstract

ABSTRACT How do the characteristics of starspots influence the triggering of stellar flares? Here, we investigate the activity of two K-type stars, similar in every way from mass to rotation periods and planetary systems. Both stars exhibit about a hundred spots; however, Kepler-411 produced 65 superflares, while Kepler-210 presented none. The spots of both stars were characterized using the planetary transit mapping technique, which yields the intensity, temperature, and radius of starspots. The average radius was (17 ± 7) × 103  and (58 ± 23) × 103 km, while the intensity ratio with respect to the photosphere was (0.35 ± 0.24) and (0.64 ± 0.15) Ic, and the temperature was (3800 ± 700) and (4180 ± 240) K for spots of Kepler-411 and Kepler-210, respectively. Therefore, spots on the star with no superflares, Kepler-210, are mostly larger, less dark, and warmer than those on the flaring star, Kepler-411. This may be an indication of magnetic fields with smaller magnitude and complexity of the spots on Kepler-210 when compared to those on Kepler-411. Thus, starspot area appears not to be the main culprit of superflares triggering. Perhaps the magnetic complexity of active regions is more important.