2000A&A...363..585R

We analyse phase-dependent variations of the photospheric lines of the magnetic B star σ Ori E and the suspected magnetic O star θ¹ Ori C. In the framework of the oblique magnetic rotator model, the observations are interpreted as the result of inhomogeneous chemical abundances - spots - at the stellar surface. This model can at least qualitatively explain the line profile variations with two spots at the magnetic poles of both stars. In the case of σ Ori E, we find the spots to be overabundant in He and depleted in metals. For θ¹ Ori C the presumed spots would be depleted both in He and in metals. For θ¹ Ori C we also discuss an alternative model with spots of enhanced abundances at the magnetic equator. This model better fits the observations. Chemical fractionation is not expected for θ¹ Ori C and the absorption lines show indications of circumstellar absorption. Therefore, the most likely interpretation of the variations observed in the absorption lines of this star is the presence of excess absorption in a circumstellar cloud and not that of a difference in chemical abundance.