Sur les origines photosphériques des structures dans les vents des étoiles chaudes et lumineuses
Major advances in the characterization of hot star winds have been achieved during the era of the International Ultraviolet Explorer (IUE) space-based mission. Of paramount interest was the detection of the enigmatic discrete absorption components (DACs): time-variable discrete absorption features propagating in the P Cygni absorption troughs of unsaturated UV resonance lines of O stars, best interpreted as spectroscopic manifestations of the presence of large-scale spiral-like corotating interaction regions (CIRs) in the stellar wind. Additionally, ground-based optical spectroscopic observations have indicated the clumpy nature of the winds of O stars. Several theoretical investigations on the origins of these two distinct types of hot star wind structures have emerged over the past three decades. Particularly, some theoretical studies have found the possibility that both of these wind structures might have their origins at the level of the stellar photosphere. Nevertheless, the last words always belong to the observations, although in this particular case a lot of work still needs to be done in that regard.  The research project conducted in the context of this thesis, essentially observational in nature, aims towards the investigation of the potential photospheric sources of those structures in hot stellar winds, by probing the low-amplitude photospheric variability of three key massive O-type stars, xi Persei [O7.5III(n)((f))], zeta Puppis [O4I(n)fp], and V973 Scorpii [O8Iaf], by means of high-precision time-dependent photometry with the Microvariability and Oscillations of STars (MOST) microsatellite, and the nanosatellites of the BRIght Target Explorer (BRITE-Constellation) mission. For zeta Pup, simultaneous ground-based intensive spectroscopic monitoring of the HeII 4686 wind emission line of the star was also performed. These efforts led to the detection of observational evidence for the presence of bright photospheric spots driving CIRs in hot stellar winds, as well as some stochastically-triggered surface structures initiating clumping at the very base of the wind. The origins of the bright spots (particularly the possibility that they might be of magnetic origin), the true nature of the randomly-excited photospheric structures (whether they are the manifestations of internal gravity waves or turbulent convection in a subsurface convection zone), as well as the universality of both of these photospheric structures in O-type stars, will be the main subjects of the next steps in this long-term quest.
Xi Persei Zeta Puppis V973 Scorpii Massive stars Starspots Stellar winds Photometry Spectroscopy Asteroseismology