Indications for anti-solar differential rotation of giant stars

Observational evidence of anti-solar differential rotation of K-type giant stars is presented. Time-series Doppler imaging based on 70 nights of spectroscopic data was used to derive the spot evolution of the stellar surfaces. The relative differential rotation parameters (a) of the binary stars IM Peg, HD 208472, and HK Lac were obtained using two techniques, cross-correlation analysis and the sheared-image method. Additionally, two previously published single giant stars are revisited and qualitatively compared to recent theoretical models. (c) 2005 WILEY-VCH Verlag GmbH O Co. KGaA, Weinheim.