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

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 $(17\pm 7)\times 10^3$ km and $(58\pm 23)\times 10^3$ km, while the intensity ratio with respect to the photosphere was $(0.35\pm 0.24)$ $I_c$ and $(0.64\pm 0.15)$ $I_c$, and the temperature was $(3800\pm 700)$ K and $(4180\pm 240)$ 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 indicate 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.

5 pages,4 Figures

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