Rotational periods of magnetic chemically peculiar stars

Magnetic chemically peculiar (mCP) stars of the upper part of the main sequence usually exhibit strictly periodic variations of their light, spectrum and magnetic field. These changes can be well explained using the oblique rotator model of the rigidly rotating star with persistent photometric spots, uneven horizontal abundance of chemical elements and dipole-like magnetic field. Long-term observations of mCP stars variability enable to determine their rotational periods with an extraordinary accuracy and reliability. We compare rotational periods of mCP stars with those of normal main sequence stars of the same spectral type and discuss the found discrepancies. We also discuss the cases of mCP stars V901 Ori, SX Ari, CU Vir, (and possibly also EE Dra), which have been reported to display an increase of their rotational periods.