Activity Cycles of the Star FK Com

Abstract

We present the results of our photometric observations of the chromospherically active star FK Com (prototype of its group of stars) acquired during the recent 5 years (2018–2023) at the INASAN observatories in Zvenigorod and Simeiz and at the Russian–Cuban observatory in Habana (Republic of Cuba). In total, we obtained 9060 estimates of the star’s brightness in the V filter between 2018 and 2023. Our measurements, as well as data from the literature and from the Kamogata Wide-field Survey (KWS) archive, were combined into a unified set containing 17 653 measurements for a time interval about 57 years long. Based on the power spectrum derived from these data, we identified possible activity cycles \({{P}_{{{\text{cycl}}}}}\), estimated by us to be 2.4, 5.63, 8, 13.6, 30, and 49 years. The dominating \({{P}_{{{\text{cycl}}}}}\) is 5.63 years long. We show that the dominating cycle found by us from extensive data to be about 5.63 years (5.4–5.8 years from other sources in the literature) can also be noticed from the analysis of earlier studies. We compared our results on the activity cycles of FK Com to data on long-term variations of two other stars of the same type, HD 199178 (V1794 Cyg) and ET Dra. Data on \({{P}_{{{\text{cycl}}}}}\) of other chromospherically active stars (from the literature and from our measurements) were used to analyze the \(\log (1{\text{/}}{{P}_{{{\text{rot}}}}}){-} \log ({{P}_{{{\text{cycl}}}}}{\text{/}}{{P}_{{{\text{rot}}}}})\) diagram. We make a conclusion on the compatibility of our determinations of activity cycles for stars of the FK Com type with data for RS CVn stars.