  Helium-peculiar magnetic chemically peculiar stars show variations of helium
abundance across their surfaces. As a result of associated atmospheric scale
height variations, the stellar surface becomes distorted, with helium-rich
regions dented inwards. Effectively, on top of flux variations due to opacity
effects, the depressed helium-rich surface regions become less bright in the
optical regions and brighter in the ultraviolet. We study the observational
effects of the aspherical surface on the light curves of a Cen. We simulate the
light curves of this star adopting surface distributions of He, N, O, Si, and
Fe derived from Doppler mapping and introducing the effect of distortion
proportional to helium abundance. We show that while most of the optical and UV
variations of this star result from flux redistribution due to the non-uniform
surface distributions of helium and iron, the reduction of light variations due
to the helium-related surface distortion leads to a better agreement between
simulated optical light curves and the light curves observed with the BRITE
satellites.
