Rapid rotation also generates strong magnetic fields by means of a dynamo that operates in the stellar interior.  In the Sun, we see the consequences of such a dynamo in magnetic concentrations at the solar surface that appear as sunspots, and in the ultraviolet and X-ray emission from the dissipation of this magnetic energy in the solar corona.  Stars like HD199143 are also expected to have "starpots", although spots in rapidly rotating stars tend to be much larger than those on the Sun and can appear at higher latitudes.  

We have mapped the spots on HD199143, and on another rapidly rotating companion in the Beta Pic moving group, a K8 dwarf CD -68 1208,  through photometric observations obtained at the South African Astronomical Observatory, and at the Australian Siding Springs Observatory. The image here shows how the light from the star is modulated by the presence of what we infer to be a large spot running from low to mid-latitudes.  The modulation is only at a level of 2%, but is enough to be able to map out the location and shape of the spot.  We can also measure the rotation rate of the star and find the rotation period of HD199243 is only 0.36 days - seventy times shorter than for the Sun. This ultra-fast rotation makes HD199143 one of the most oblate late-type stars known. CD -68 1208 is similarly fast, with a period of 0.35 days.  From a repeat series of observations twenty days later than the first, we find that the spot area on HD199243 changed by about 7%, likely as a result of the continuous emergence of magnetic field at the stellar surface.  This work was lead by ex-SAO postdoc Dr. David Garcia-Alvarez, now at the Instituto de Astrofisica de Canarias, in Tenerife, Spain, and was published in Astronomy & Astrophysics, volume 533 in 2011.