Small-scale vortices in stellar atmospheres

Over the past two decades, observations and numerical simulations revealed the ubiquitous presence of small-scale vortical motions in the quiet solar atmosphere. Similar swirling flows can be expected to occur in other stellar atmospheres than solar. We investigate the presence and properties of small-scale vortices in the atmosphere of K8, K2, G2, and F5 main sequence stellar models. For that purpose, we analyze numerical simulations encompassing a small region around the stellar surface, ranging from the top layers of the convection zone to the upper photosphere. The simulations are realized with the three-dimensional radiative magneto-hydrodynamical CO5BOLD code and we employ a state-of-the-art automated algorithm for the identification of vortices. Numerous vortical motions are identified in all four stellar models. We present a statistical analysis on the main properties of these swirls, namely their average size, period of rotation, and number density. We find that the fastest vortices are found in the coolest stellar models and we derive a simple scaling law relating the effective temperature of the star to the typical period of rotation of a vortex. Ultimately, we want to study how swirl properties vary according to the strength of the surface magnetic field, which is amplified via the action of a small-scale turbulent dynamo.