ACTIVITY CYCLES OF FK COM

Abstract

New results of photometric observations of the chromospherically active star FK Com (a prototype of the group of the same name) performed during the past 5 years (2018–2023) at the INASAN observatories in Zvenigorod, Simeiz Observatory INASAN and Russian–Cuban Observatory in Havana, Republic of Cuba, are presented. In total during this observation interval we obtained 9060 estimates of the brightness of the star in V band. Our measurements as well as data from the literature and from the Kamogata Wide-field Survey (KWS) archive were combined into the array comprising 17 653 measurements in an interval of about 57 years. Based on the power spectrum constructed from these data, P values of the cycle activity have been established, which according to our estimate are equal to 2.4, 5.63, 8, 13.6, 30 and 49 years. The dominant is the P cycle lasting 5.63 years. It is shown that this dominant cycle with a period of about 5.63 years found by us according to more extensive data (5.4–5.8 years in other sources) can be traced in the results of the analysis of previous studies. The results on the activity cycles of FK Com are compared with data on the long-term variability of two more stars of the type under consideration – HD 199178 (V1794 Cyg) and ET Dra. Based on the data on the P cycle of other chromospherically active stars (according to literature sources and our measurements) a diagram \(\log (1{\text{/}}{{P}_{{{\text{rot}}}}}){\kern 1pt} - {\kern 1pt} \log ({{P}_{{{\text{cycl}}}}}{\text{/}}{{P}_{{{\text{rot}}}}})\) is analyzed. The conclusion about the comparability of the values of the activity cycles of the FK Com type stars with the data for stars of the RS CVn type is made.