BRITE-Constellation high-precision time-dependent photometry of the early O-type supergiant ζ Puppis unveils the photospheric drivers of its small- and large-scale wind structures

Abstract

From 5.5 months of dual-band optical photometric monitoring at the 1 mmag level, BRITE-Constellation has revealed two simultaneous types of variability in the O4I(n)fp star ζ Puppis: one single periodic non-sinusoidal component superimposed on a stochastic component. The monoperiodic component is the 1.78 d signal previously detected by Coriolis/SMEI, but this time along with a prominent first harmonic. The shape of this signal changes over time, a behaviour that is incompatible with stellar oscillations but consistent with rotational modulation arising from evolving bright surface inhomogeneities. By means of a constrained non-linear light curve inversion algorithm we mapped the locations of the bright surface spots and traced their evolution. Our simultaneous ground-based multi-site spectroscopic monitoring of the star unveiled cyclical modulation of its He ii λ4686 wind emission line with the 1.78-day rotation period, showing signatures of Corotating Interaction Regions (CIRs) that turn out to be driven by the bright photospheric spots observed by BRITE. Traces of wind clumps are also observed in the He ii λ4686 line and are correlated with the amplitudes of the stochastic component of the light variations probed by BRITE at the photosphere, suggesting that the BRITE observations additionally unveiled the photospheric drivers of wind clumps in ζ Pup and that the clumping phenomenon starts at the very base of the wind. The origins of both the bright surface inhomogeneities and the stochastic light variations remain unknown, but a subsurface convective zone might play an important role in the generation of these two types of photospheric variability.

3D MHD simulations and synthetic radio emission from an oblique rotating magnetic massive star

“…Separate simultaneous spectroscopic observations led them to infer the action of corotating interaction regions (CIRs). While no surface spots are present in our simulation, the modelling of ζ Puppis by Ramiaramanantsoa et al (2017) to explain the BRITE-Constellation observations, results in spiral structures of a similar nature to those in Fig. 6.…”

Envelope Convection, Surface Magnetism, and Spots in A and Late B-type Stars

“…The FeCZ should play a role in various observational effects such as line profile variability, discrete absorption components and photometric variability, amongst others (Cantiello et al 2009). In particular, the bright spots associated with emergent magnetic fields predicted by Cantiello & Braithwaite (2011) might have been recently observed by the MOST and BRITE missions (Ramiaramanantsoa et al 2014(Ramiaramanantsoa et al , 2018a). Short-lived, co-rotating bright spots can explain part of the photometric variability in a large fraction of the observed OB targets, and therefore could be an ubiquitous feature of these stars.…”

A Deep Exposure in High Resolution X-Rays Reveals the Hottest Plasma in the ζ Puppis Wind

“…As such, this O4If(n)p star (Sota et al 2011) has been the target of many important studies to characterize its variability and properties. Much of this work was summarized in a recent analysis of optical spectroscopy and highprecision photometry by Ramiaramanantsoa et al (2018), to whom we refer readers for relevant background discussion about the target star.…”