Soutenance de thèse de Jordan PHILIDET le mercredi 8 septembre 2021

Titre de la thèse

"Study of the coupling between turbulent convection and solar-like oscillations"

Abstract

Asteroseismology has revolutionised our understanding of stellar interiors, through the observations of oscillations on the surface of stars. In solar-like oscillators, the turbulent motions caused by convection have a substantial impact on the properties of these oscillations, whether on their frequencies or their amplitude. This turbulence/oscillation coupling offers a unique way to constrain the little-understood properties of stellar convection using the observed acoustic mode properties, a task which requires a thorough theoretical understanding of this coupling. The first part of this thesis focuses on the asymmetry displayed by the line profiles of solar-like oscillations, which carries the signature of the localisation of the driving source close to the surface of the star. I will present a formalism designed to give quantitative predictions for solar-like mode asymmetry, and to directly relate the observed asymmetries to the underlying properties of turbulence in this region. I will show how this formalism gives us insight into the origin of asymmetry, its reversal between the velocity and intensity observables, as well as on the intensity/velocity amplitude ratios. In a second part, I more generally investigate a new modelling approach for turbulence/oscillation coupling, based on Lagrangian stochastic models of turbulence. I will jointly present analytical developments and a numerical implementation based on this class of models, which allow me to simultaneously relate the excitation rate of solar-like p-modes, their damping rate, as well as the modal surface effects affecting their frequency, directly to the statistical properties of the underlying turbulent velocity field, thus shedding a new light upon the physical processes at hand.