  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, cool cyclonic vortices
are preferred, whereas for rapid rotation, warm anti-cyclonic vortices are
favored. 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.
