Studying Wolf-Rayet Stars Through Their
Wind Structure and Circumstellar Medium
The most massive stars in the Universe live only a few million years but have a strong impact on their surrounding medium. These luminous and hot stars are born deep in molecular clouds and, even before being fully formed, develop a strong wind, which persists in all phases of their evolution. Through these outflows, they chemically enrich the gas and impart to it a large amount of energy and momentum. This leaves in the surrounding medium information-rich imprints in the form of ejected nebula and wind-blown bubbles, which trace the mass-loss history of the star as it undergoes its various evolutionary phases before ending its life in a spectacular supernova explosion. These winds enable massive stars to play a pivotal role in governing the evolution of gas, dust and ultimately of stellar populations composing galaxies.
I work principally on Wolf-Rayet (WR) stars, which are massive stars that have reached the core helium-burning phase. I am particularly interested in large-scale structures that form in the winds of ~20% of them, called Corotating Interaction Regions (CIRs). These form in radiation driven flows when a perturbation at their base generates regions of different velocities that collide when the star rotates, producing a large spiral-like structure encompassing zones of higher and lower densities and velocities compared to the ambient wind. In addition to the fact that the source of the perturbations is unknown (magnetic, pulsations), these structures have an impact on the angular momentum of the star, which affects its evolution. My goal is to identify more WR stars with CIRs (only three are confirmed) using intense monitoring campaigns, from which I will also characterize their properties. To do this, I work on theoretical aspects that enable me to more accurately interpret the observations. Once more WR stars with CIRs are identified, I will search for links between various physical stellar parameters and their presence and properties to gain knowledge on the mechanisms from which they originate.
I also use the wide-field optical imaging Fourier-Transform Spectrograph, SITELLE, on the Canada-France-Hawaii Telescope to characterize with high spatial extent and resolution, the circumstellar medium (CSM) around WR stars. This state-of-the-art instrument is ideal to obtain maps of the extinction, density, temperature and abundances of the CSM, which can be used to characterize the chemical enrichment, asymmetries and kinematics of the mass ejections that occurred in the intermediate phases between the main sequence and WR stages. The surface abundances of massive stars and thus their CSM are affected by various processes during their evolution and by binary effects such as tidally induced mixing or mergers. By comparing the CSM characteristics with models of single and binary stars, one can gain insight into massive-star evolution for which many aspects still remain misunderstood.
