Variability of Superflare Frequency of Sun Like Stars

Abstract

This is a statistical study of the variability in the frequency of superflares in 46 stars of the solar type observed with the Kepler orbital observatory. Two possible scenarios for changes in the superflare frequency are examined. In the first, the time sequence of superflares is treated as a piecewise stationary Poisson process. 5 stars are found to have statistically significant changes by several times in their superflare frequency. The times at which the frequency changes are accompanied by changes in the behavior of a star’s brightness outside the flares. For a short time the star’s brightness becomes irregular, with a substantial reduction in its luminosity amplitude. In the second scenario, the time sequence of the superflares is treated as a Poisson process with a periodic parameter (the superflare frequency). This scenario confirms the existence of a possible periodicity of the superflare frequency with a period equal to the period of the star’s orbital or axial rotation. The star KIC 7264976 is found to have a frequency periodicity with a period that is the same as the possible period of its orbital rotation. A frequency periodicity with a period equal to the probable axial rotation period is found for the star KIC 10422252.