Understanding the photometric variability of {\zeta} Ori Aa

TL;DR

This study investigates the brightness variations of the magnetic O-type supergiant $$ Ori Aa using multi-colour photometry and spectroscopy, confirming known rotation signals and identifying new environmental variability frequencies.

Contribution

It provides new insights into the variability mechanisms of $$ Ori Aa by combining photometric and spectroscopic data to identify rotation and circumstellar environment frequencies.

Findings

Confirmed the rotation frequency $f_{rot} = 0.15 \, c/d$ and its harmonics.

Detected a new frequency $f_{env} = 0.10 \, c/d$ related to the circumstellar environment.

Linked circumstellar variations to differences in the observed lightcurves.

Abstract

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