A BRITE view on the hot early O-type supergiant Zeta Puppis: Probing the photospheric drivers of its wind structures.

Tahina RAMIARAMANANTSOA ( Université de Montréal )

The hottest and brightest star visible to the naked-eye in the celestial sphere is the fast-rotator single runaway early-O-type blue supergiant going under the name of Zeta Puppis. Owing to its brightness, proximity and status of single star, Zeta Pup has become a key star for understanding the properties of O-type stars and hot stellar winds. I will present the results of a coordinated optical campaign aiming at probing the photospheric origins of wind structures in Zeta Pup, involving long-term precision dual band space photometry with the BRITE-Constellation nanosatellites and contemporaneous multi-site ground-based spectroscopic monitoring. The only period that comes out of the Fourier analysis of the BRITE light curves above the 4 sigma detection level in both red and blue filters is a 1.8 d period previously detected by Coriolis/SMEI, but this time along with its first harmonic at ~21.6 h, resulting in a monoperiodic non-sinusoidal shape-varying signal showing two consecutive bumps compatible with signatures of rotational modulation due to the presence of bright spots at the stellar surface that would be the drivers of large-scale Corotating Interaction Regions in the stellar wind. The residual light curves after removal of the 1.8 d signal show random variations coherent in both filter passbands that could be the signatures of random acoustic waves originating from a subsurface convection zone due to the partial ionisation of iron previously suspected to drive the formation of clumps in the stellar wind.