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Description
HD 208472 is among the most active RS CVn binaries with cool starspots. Decade-long photometry had shown that the spots seem to change their longitudinal appearance with a period of about six years, coherent with brightness variations. Our aim is to spatially resolve the stellar surface of HD 208472 and related the photometric results to the true longitudinal and latitudinal spot appearance. Furthermore, we investigate surface differential rotation pattern of the star. We employ three years of high resolution, high S/N spectroscopic data from the STELLA robotic observatory and determine new and more precise stellar physical parameters. Pre-calculated synthetic spectra are fit to each of these spectra and new spot-corrected orbital elements are given. A sample of 34 absorption lines per spectrum is used to calculate mean line profiles with a S/N of several hundred. A total of 13 temperature Doppler images are reconstructed from these line profiles with the inversion code iMap. Differential rotation is investigated by cross-correlating successive Doppler images in each observing season. Spots on HD 208472 are distributed preferably at high latitudes and less occasionally around mid-to-low latitudes. No polar-cap like structure is seen at any epoch. We observed a flip-flop event between 2009 and 2010, manifested as a flip of the spot activity from phase 0.0 to phase 0.5, while the overall brightness of the star continued to increase and reached an all-time maximum in 2014. Cross-correlation of successive Doppler images suggests a solar-like differential rotation which is ~15 times weaker in strength compared to the Sun.
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