ACTIVITY CYCLES OF SINGLE G5 III-IV GIANT HD 199178

A unique series of photometric data has been obtained for a period of more than a hundred years for the rapidly rotating single G5 III–IV giant HD 199178 (V1794 Cyg) belonging to the group of stars of the FK Com type. Our analysis of the long-term periodicity of the activity of this star is based on all available measurements of its brightness in B filter. To assess the brightness of HD 199178 in the era preceding photoelectric and CCD observations measurements were made using photographic plates from the archive of the SAI MSU at the Krasnopresnenskaya Observatory of Moscow State University in Moscow (4 plates taken from 1898 to 1903 and 41 plates obtained from 1935 to 1958). As a result, a total of 2142 estimates of the brightness of the star in the B filter were considered . They have a unique duration of 118.3 years and cover the time interval from 1898 to July 2016. Evidence of the existence of long-term cycles of photometric variability with values of the order of 25–60 years has been found. It is assumed that there are possible activity cycles of 2000, 3165, 5050, 9000 and 21600 days (5.5, 8.7, 16.6, 24.7 and 59.2 years). The results obtained are compared with other estimates of activity cycles of HD 199178. The existence of a cycle of 8.7–9 years should be recognized as the most reliable. It is found that to combine data into a single array the conversion of values B into values V using the average value of the color index (\(B{\kern 1pt} - {\kern 1pt} V\)) is not possible due to changes (including cyclical) of (\(B{\kern 1pt} - {\kern 1pt} V\)) with time.