Understanding the photometric variability of ζ Ori Aa

Abstract

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

7 pages, 3 figures, proceedings for the Second BRITE-Constellation Science Conference