1996A&A...312..539S

We have obtained a long series of optical spectra and new IUE spectra of θ¹Ori C, the brightest star in the Orion Trapezium and the main source of ionization of the Orion nebula (M 42). With these data, we have improved the accuracy of the period of the optical emission-line variations and the UV stellar-wind absorption-line variations. We find a period of 15.422 ± 0.002 days. The high accuracy of the period makes it possible to phase correctly our new data and archival IUE data obtained more than fifteen years ago. The stellar wind absorption is weakest when the emission lines have maximum strength. In addition, we have detected periodic variations in the strength of photospheric spectral lines. Lines from HeI, HeII, C IV and OIII all vary in phase. The absorption of these lines is strongest when the emission is at its maximum. These variations appear to be due to a rotating surface feature which spatially coincides with the emission region.