Understanding the photometric variability of ζ Ori Aa

We studied the variability of the magnetic O-type supergiant ζ Ori Aa using multi-colour BRITE photometry. We confirmed the known rotation frequency f_{rot} = 0.15 ± 0.02 c/d, and detected some of its higher harmonics, of which 4f_{rot} is compatible with the known DAC recurrence timescale. Thanks to simultaneous high-resolution CHIRON spectroscopy, we could identify another frequency f_{env} = 0.10 ± 0.02 c/d, caused by the circumstellar environment. Variations in the circumstellar environment are believed to cause the observed difference between the BRITE lightcurves.

Based on data collected by the BRITE Constellation satellite mission, designed, built, launched, operated and supported by the Austrian Research Promotion Agency (FFG), the University of Vienna, the Technical University of Graz, the Canadian Space Agency (CSA), the University of Toronto Institute for Aerospace Studies (UTIAS), the Foundation for Polish Science & Technology (FNiTP MNiSW), and National Science Centre (NCN).

Based on CHIRON spectra collected under CNTAC proposal CN2015A-122.),