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

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Monthly Notices of the Royal Astronomical Society: Letters
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© 2023 The Author(s) Published by Oxford University Press on behalf of Royal Astronomical Society.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.
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