Modeling line profile variations of sigma Ori E and theta(1) Ori C

We analyse phase-dependent variations of the photospheric lines of the magn etic B star sigma Ori E and the suspected magnetic O star theta (1) Ori C. In the framework of the oblique magnetic rotator model, the observations ar e interpreted as the result of inhomogeneous chemical abundances - spots - at the stellar surface. This model can at least qualitatively explain the l ine profile variations with two spots at the magnetic poles of both stars. In the case of a Ori E, we find the spots to be overabundant in He and depl eted in metals. For theta (1) Ori C the presumed spots would be depleted bo th in He and in metals. For theta (1) 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 t heta (1) Ori C and the absorption lines show indications of circumstellar a bsorption. Therefore, the most likely interpretation of the variations obse rved in the absorption lines of this star is the presence of excess absorpt ion in a circumstellar cloud and not that of a difference in chemical abund ance.