Discovery of cyclic spot activity on the G8 giant HD 208472

Details Discovery of cyclic spot activity on the G8 giant HD 208472 Discovery of cyclic spot activity on the G8 giant HD 208472

Aug 2010

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2010an....331..794o&link_type=abstract

Astronomische Nachrichten, Vol.331, Issue 8, p.794

Astronomy and Astrophysics

Astronomy

1

Binaries: Close, Stars: Activity, Stars: Individual (Hd 208472), Starspots, Techniques: Photometric

Scientific paper

% We present and analyze 17 consecutive years of U BV RI 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 period-search 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=Δ P/P of 0.004±0.010, which would be fifty times weaker than on the Sun.
Based on data obtained with the Amadeus T7 Automatic Photoelectric Telescope at Fairborn Observatory, jointly operated by the University of Vienna and AIP, the Tennessee State University T3 0.4 m APT at Fairborn Observatory, operated by Tennessee State University, and the telescopes of the Ege University Observatory in Izmir.

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