Time-series Doppler imaging of the red giant HD 208472. Active longitudes and differential rotation

Abstract

HD 208472 is among the most active RS~CVn binaries with cool starspots. Decade-long photometry has 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 relate the photometric results to the true longitudinal and latitudinal spot appearance. Furthermore, we investigate the surface differential rotation pattern of the star. We employed three years of high-resolution spectroscopic data with a high signal-to-noise ratio (S/N) from the STELLA robotic observatory and determined new and more precise stellar physical parameters. Precalculated synthetic spectra were fit to each of these spectra, and we provide new spot-corrected orbital elements. A sample of 34 absorption lines per spectrum was used to calculate mean line profiles with a S/N of several hundred. A total of 13 temperature Doppler images were reconstructed from these line profiles with the inversion code iMap. Differential rotation was investigated by cross-correlating successive Doppler images in each observing season. Spots on HD 208472 are distributed preferably at high latitudes and less frequently 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 that is ~15 times weaker than that of the Sun.

12 pages, 11 figures

References in corpus (9)

• A grid of MARCS model atmospheres for late-type stars I. Methods and general properties
• Scaled solar tracks and isochrones in a large region of the Z-Y plane I. From the ZAMS to the TP-AGB end for 0.15 - 2.5 Mo stars
• The Magnetic Topology of the Weak-Lined T Tauri Star V410 - A Simultaneous Temperature and Magnetic Field Inversion
• Spot evolution on the red giant star XX Triangulum. A starspot-decay analysis based on time-series Doppler imaging
• A fast method for Stokes profile synthesis -- Radiative transfer modeling for ZDI and Stokes profile inversion
• Zeeman-Doppler Imaging of Late-Type Stars -- The Surface Magnetic Field of II Peg
• Differential rotation on both components of the pre main-sequence binary system HD 155555
• Antisolar differential rotation of the K1-giant sigma Geminorum revisited
• Anti-solar differential rotation on the active sub-giant HU Virginis

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• The first Doppler imaging of the active binary prototype RS Canum Venaticorum
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• Starspots on eclipsing giant stars I.: The sample and eclipse mapping examples
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