Starspots due to large-scale vortices in rotating turbulent convection

Details Starspots due to large-scale vortices in rotating turbulent convection Starspots due to large-scale vortices in rotating turbulent convection

2011-06-29

arxiv.org/abs/1106.6029v1

Astronomy and Astrophysics

Astrophysics

Solar and Stellar Astrophysics

8 pages, 8 figures, submitted to ApJ. Version with higher resolution figures can be found at this http://www.helsinki.fi/~kapy

Scientific paper

We study the generation of large-scale vortices in rotating turbulent convection by means of Cartesian direct numerical simulations. We find that for sufficiently rapid rotation, cyclonic structures on a scale large in comparison to that of the convective eddies, emerge, provided that the fluid Reynolds number exceeds a critical value. For slower rotation, cold cyclonic vortices are preferred, whereas for rapid rotation, warm anti-cyclonic vortices are favoured. In some runs in the intermediate regime both types of cyclones co-exist for thousands of convective turnover times. The temperature contrast between the vortices and the surrounding atmosphere is of the order of five per cent. We relate the simulation results to observations of rapidly rotating late-type stars that are known to exhibit large high-latitude spots from Doppler imaging. In many cases, cool spots are accompanied with spotted regions with temperatures higher than the average. In this paper, we investigate a scenario according to which the spots observed in the temperature maps could have a non-magnetic origin due to large-scale vortices in the convection zones of the stars.

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