Activity Cycles of a Single G5 III–IV Giant HD 199178

Abstract

Abstract We obtained a unique series of photometric data for more than a hundred years for a rapidly rotating single G5 III–IV giant HD 199178 (V1794 Cyg), belonging to FK Com type stars. The analysis of the long-term variation of the activity of this star in the filter $$B$$ is based on all measurements available in literary sources. To evaluate the brightness of HD 199178 in the era preceding photoelectric and CCD-observations, the measurements of photographic plates from the SAI MSU archive were shot at the Krasnopresnenskaya Observatory of Moscow State University in Moscow (4 records shot from 1898 to 1903, and 41 records for the period from 1935 to 1958) were performed. As a result, a total of 2142 assessments of the brightness of the star in the filter $$B$$ were received. They have a unique duration of 118.3 yr and cover the time interval from 1898 to July 2016. Evidence was found of the existence of long-term cycles of photometric variability lasting for about 25‒60 years. We put forward an assumption on existence of possible activity cycles of 2000, 3165, 5050, 9000, and 21 600d (respectively, 5.5, 8.7, 16.6, 24.7, and 59.2 years). The results are compared with other estimates of activity cycles in HD 199178. The most reliable should be recognizing the existence of a cycle lasting 8.7‒9 years. It was found that in order to combine data into a single array, the convertation of $$B$$ magnitudes into $$V$$ magnitudes using the average value of the color index (B–V) is not possible due to the changes (including cyclic) of color index (B–V) over time.