SUPERFLARES AND CYCLES AS STAGES OF THE EVOLUTION OF STELLAR ACTIVITY

Abstract

Current observations allow us to consider changes of the solar-stellar activity in the evolutionary aspect. Development of active processes is determined by physical parameters of a star, when it arrives to the main sequence. At birth, low-mass stars in the open cluster have a large dispersion of rotation, which decreases rapidly due to the fact that rapid rotators are slowed down more effectively. During the rst 1 Gyr, the initial dispersion almost disappears. To this epoch, magnetic fields are formed that evolve in a close correlation with rotation and determine the pattern of activity over the next billions of years. Distinctions between the saturated regime of activity intrinsic to the youngest, fast rotating low-mass stars and stars with the solar-type activity, when a cycle begins to be established, are considered. Changes in the regime of activity are discussed in the context revealing epochs of the cycle formation on stars of different spectral types.

Discovery of the most powerful non-stationary phenomena like superflares on G-type stars during the Kepler mission is a challenge that outlined the new challenges to be addressed. Now it is clear that the largest superflares occur rather on fast rotators, i.e. on stars, whose activity is in the saturated regime and which possess the maximal magnetic activity. Joint analysis of observations of superflares and available data on stellar magnetic fields on solar-type stars gives a chance to estimate the maximal possible energy of stellar flares and to understand their origin