Activity and cold spots on the surface of G-type superflare stars

Abstract

Based on the high precision photometric observations of the Kepler space telescope, we have investigated the properties of the active regions (cold spots) on the surface of 279 stars of the spectral class G, for which 1547 superflares with energies in the range of 10³³–10³⁶ erg have been revealed. The main conclusion of our study is the quantitative estimation of the increased surface spottedness of superflare stars, which indicates enhancedmagnetic activity of these objects. The increased spottedness on the surfaces of the studied stars was confirmed based on two independent estimations of stellar brightness variations. In addition, it was concluded that superflare stars do not stand out in the common dataset of differential rotation parameters. Based on the data considered, no correlation was found of the spottedness parameters or the differential rotation parameters with the characteristics of these objects—their Rossby numbers and superflare energy. Additionally, the correlation between the superflare energy and the inverse Rossby number was considered. None of these comparisons gave an indication for the presence of any obvious correlation. The results of the analysis of five stars with a few dozen flares registered indicate that for the same star whereas spottedness S variations are small, significant changes in the superflare energy can be achieved. On the example of KIC 10422252, we show that at sixfold S variations, the flare energy varies by orders of magnitude at any given S value.