Measuring differential rotation of the K-giant ζ Andromedae ⋆
1 Konkoly Observatory of the Hungarian Academy of Sciences, Konkoly Thege út 15-17, 1121 Budapest XII, Hungary
2 Niels Bohr Institute, University of Copenhagen, Juliane Maries Vej 30, 2100 København Ø, Denmark
3 Finnish Centre for Astronomy with ESO (FINCA), University of Turku, Väisäläntie 20, 21500 Piikkiö, Finland
4 IRAP-UMR 5277, CNRS & Univ. de Toulouse, 14 Av. E. Belin, 31400 Toulouse, France
5 Observatoire de Haute-Provence, OHP/CNRS, 04870 Saint-Michel l’Observatoire, France
6 University of Michigan, 941 Dennison Building, 500 Church Street, Ann Arbor, MI 48109-1090, USA
7 ESO, Karl-Schwarzschild Strasse 2, 85748 Garching bei München, Germany
8 LATT-UMR 5572, CNRS & Univ. P. Sabatier, 14 Av. E. Belin, 31400 Toulouse, France
Received: 29 September 2011
Accepted: 20 January 2012
Aims. We investigate the temporal spot evolution of the K-giant component in the RS CVn-type binary system ζ Andromedae to establish its surface differential rotation.
Methods. Doppler imaging was used to study three slightly overlapping spectroscopic datasets, which were obtained independently at three different observing sites. Each dataset covers one full stellar rotation with good phase coverage, which results in a continuous coverage of almost three stellar rotations (Prot = 17.8 d). Therefore, these data are well-suited for reconstructing surface temperature maps and studying temporal evolution in spot configurations. Surface differential rotation was measured by the means of cross-correlation of all possible image pairs.
Results. The individual Doppler reconstructions agree well in the revealed spot pattern, recovering numerous low-latitude spots with temperature contrasts of up to ≈1000 K with respect to the unspotted photosphere, and also an asymmetric polar cap that is diminishing with time. Our detailed cross-correlation study consistently indicates solar-type differential rotation with an average surface shear α ≈ 0.055, in agreement with former results.
Key words: stars: activity / stars: imaging / stars: late-type / starspots / stars: individual: ζAndromedae
© ESO, 2012