Anti-solar differential rotation on the active K-giant $\mathsf{\sigma}$ Geminorum

Abstract

The active K1 giant σ Gem and its differential surface rotation is revisited. We refine our previous inconclusive result by recovering the spot migration pattern of this long-period RS CVn-type binary through application of the technique of “average cross-correlation of contiguous Doppler images” to a set of six Doppler images from 3.6 consecutive rotation cycles. We find an anti-solar differential rotation law with a shear of -0.022±0.006. We also find evidence of a poleward migration trend of spots with an average velocity of ≈300 m s-1.