Spot evolution and differential rotation of the ultrafast rotator Speedy Mic

Abstract

The Sun shows a variety of transient surface features which are summarized as solar activity. Activity phenomena, apparently similar to the solar case, are also observed on stars other than the Sun. Stellar activity is closely related to magneto-hydrodynamic processes in a stars̉ convection zone. A dynamo is believed to operate in the outer convection zone of solar-like stars, generating magnetic fields by complex motions of the convecting plasma under the influence of rotation. Differential (i.e. non-rigid) rotation of the stellar surface is an important indicator of the overall dynamics of a stars̉ outer convection zone. Sunspots are a conspicuous token of solar activity; dark spots can also be observed on the surface of stars other than the Sun. To which degree starspots are analogues of sunspots is presently only poorly known; the processes governing their lifetime and structure are largely unexplored. Doppler imaging overcomes the diffraction-limitations of direct and interferometric imaging techniques by making use of information that is modulated into a star’s spectrum due to its rotation. Doppler imaging is currently the only method to produce well-resolved images of solar-like stars. After a selective review of the observational and theoretical foundation,