1999A&A...348..924K

We present the distribution of helium, magnesium, silicon, chromium and iron on the surface of the fast rotating magnetic B9pSi star CU Virginis, obtained with a Doppler Imaging inversion code. A clearly defined helium spot coincides with the position of one magnetic pole whereas silicon, chromium and iron accumulate in regions where the magnetic field lines are dominantly horizontal in the stellar atmosphere. The distribution of magnesium is significantly different compared to the other elements. The Hδ line varies in phase with the helium spot and the magnetic pole and the line profiles can be fitted within the observational errors with model atmospheres of constant T_eff of 12500K, but different surface gravity. We compare our observations with current concepts for diffusion in magnetic chemically peculiar stars and find good agreement.