Spot and flare activity of single G5 III IV giant HD 199178 from TESS observations

The aim of our work is to study the activity of the FK Com type star rapidly rotating G5 III IV giant HD 199178 (V1794 Cyg) on the base of available photometric data from TESS mission in five sectors. The light curves of the star characterized the variability caused by rotational modulation due to the presence of cool spots on the surface, power spectra and phase diagrams are studied. The dominant peak corresponds to the photometric period P = 3.28d ± 0.12d. It is suggested that the value of P decreases over time (over an interval of about 40 years) from 3.337d up to 3.28d may be due to the long-term evolution of the positions of the active areas (spots) on the surface of a differentially rotating star. The changes in the amplitude of the brightness variability and the shape of the phase curves of HD 199178 were analyzed and it was found that the fraction of the star’s surface occupied by spots varied from 7 to 12% of its surface area. The flare activity of the star has been studied. The parameters of the amplitude, duration and energy of the flares are determined for two of them. One of the considered flares is the strongest during the observations in five sectors (5.1 × 1035 erg) and in magnitude can characterize the upper limit of the flare energies in a given state of star activity. Maps of the surface temperature inhomogeneities of the star are constructed.