Discovery of cyclic spot activity on the G8 giant HD 208472

We present and analyze 17 consecutive years of UBVRI time-series photometry of the spotted giant component of the RS CVn binary HD 208472. Our aim is to determine the morphology and the evolution of its starspots by using periodsearch techniques and two-spot light-curve modelling. Spots on HD208472 always occur on hemispheres facing the observer during orbital quadrature and flip their location to the opposite hemisphere every approximately six years. The times when the spots change their preferential hemisphere correspond to times when the light curve amplitudes are the smallest and when abrupt changes of the photometric periods are observed. During these times the star is also close to a relative maximum brightness, suggesting a vanishing overall spottedness at each end of the previous cycle and the start of a new one. We find evidence for a 6.28±0.06-yr brightness cycle, which we interpret to be a stellar analog of the solar 11-year sunspot cycle. We also present clear evidence for a brightening trend, approximated with a 21.5±0.5-yr period, possibly due to a stellar analog of the solar Gleissberg cycle. From the two-spot modelling we also determine an upper limit for the differential-rotation coefficient of α = ΔP/P of 0.004±0.010, which would be fifty times weaker than on the Sun (© 2010 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim