The Activity of Stars with Planetary Systems and Its Impact on the Loss of Atmosphere by Hot Exoplanets
И. С. Саванов, V. I. Shematovich
Abstract
Abstract The review presents the results of a wide range of studies on modeling the atmospheres and shells of exoplanets and studying the processes associated with the activity of the parent star, performed at the Institute of Astronomy of the Russian Academy of Sciences in recent years. The developed methods of analyzing superflares in solar-type stars are applied to stars with planetary systems and the obtained estimates are used to detail the conditions of extreme stellar activity in the study of atmospheric losses for Earth-type planets in low orbits—super-Earths and sub-Neptunes. The results of calculations of the rate of atmospheric loss for exoplanets in orbits close to the parent star (close-in exoplanets) are presented and it is shown that under conditions of a high level of stellar radiation rigidity, and even more so under conditions of a stellar flare, the contribution of exothermic photochemistry processes to the formation of a flow of supra-thermal hydrogen atoms escaping from the atmosphere becomes significant and comparable to the flow of hydrodynamic outflow. Accordingly, this source of supra-thermalhydrogen atoms should be included in modern aeronomic models of physical and chemical processes in the upper atmospheres of hot exoplanets. Taking into account the contribution of supra-thermal particles in the aeronomic model made it possible to clarify the heating rates of atmospheric gas due to the absorption of hard radiation from the parent star. This, in turn, made it possible to more accurately calculate the values of the rate of mass loss by atmospheres and, accordingly, to study the evolutionary properties of the atmospheres of hot exoplanets. It is also important to note that the kinetic and aeronomic models presented in the review, developed in recent years at the Institute of Astronomy of the Russian Academy of Sciences, will be used to analyze and interpret existing and expected observations of the atmospheres of Earth-type exoplanets. Such work will allow to impose additional restrictions on the models and thereby make them more reliable.