Activity of K-Dwarf HIP 113103 and Atmospheric Losses of Its Exoplanets

We present the results of analyzing the activity manifestations of the K3 V spectral type dwarf HIP 113103 (HD 216530) and estimate the matter loss from the atmospheres of two of its planets. HIP 113103 can be classified as a relatively young object with an age of about 470 million years—1 billion years. Using the standard method, based on the observed data from the TESS mission, we estimated the areas of spots on the surface of the star, which exceed the maximum area of spots on the Sun and are 6100 and 4950 MSH for sectors 1 and 28, respectively. According to the data from the observation archive of the All Sky Automated Survey, the activity cycles of HIP 113103 have been established to last about 610, 825, and 1030 days (1.7, 2.3, and 2.8 years, respectively). Both planets in the stellar system HIP 113103 are characterized as objects with radii of 1.829\(R_{\oplus}\) and 2.400\(R_{\oplus}\), with periods of 7.6 and 14.2 days, respectively, lying on opposite sides of the Fulton Gap in the ‘‘Period—Radius’’ diagram. The loss of matter from the planetary atmospheres was calculated using an approximation formula corresponding to the energy-limited atmospheric loss model. To estimate the flux of XUV photons, analytical dependences were used connecting flux values and the \(\log R^{\prime}_{\textrm{HK}}\) parameter. It was found that the values \(\dot{M}\) values for planets b and c are equal to \(2.8\times 10^{8}\) g s\({}^{-1}\) and \(1.9\times 10^{8}\) g s\({}^{-1}\), respectively. The planet HIP 113103 b attracts special attention because, with its radius \(R_{p}=1.829R_{\oplus}\), it belongs to a small population of planets with the radii \(1.5R_{\oplus}<R_{p}<2.0R_{\oplus}\), which characterizes the evolution of super-Earths and mini-Neptunes. HIP 113103 c has a radius of \(R_{p}=2.40R_{\oplus}\) and an equilibrium temperature of \(585\pm 10\) K which characterizes the object as an already established warm mini-Neptune. A comparison of the properties of planets b and c is of interest, since they belong to the same system, are irradiated by the same star, probably have similar ages and conditions of formation, etc.