Shear-driven turbulent transport in stellar radiative zones
Intervenant : Vincent Prat
Stellar models play an important role in many fields of astrophysics, from the chemical evolution of galaxies to the characterisation of planetary systems. However, these models present large uncertainties due to our lack of understanding of stellar evolution. In particular, magneto-hydrodynamical processes that transport chemical elements and angular momentum in stellar interiors are often poorly (or not at all) modelled in stellar evolution codes. In this context, numerical simulation is a crucial tool to provide additional constraints on such models and thus to improve the predictive power of stellar evolution theory.
Turbulence generated by the shear instability in stellar radiative zones is one of the processes that have been thought to induce transport in stellar interiors. This transport, often called rotational mixing, was first modelled by Zahn (1992, A&A, 265, 115) using phenomenological arguments. Recent asteroseismic observations show that such models may underestimate the transport by several orders of magnitude. The work that I will present consists in performing numerical simulations of the shear instability to test existing models and in proposing new prescriptions. In particular I will discuss the effects of the key physical ingredients that are thermal diffusion, stable stratification (thermal and chemical), and viscosity on vertical transport. I will also present a new theoretical model of horizontal transport that includes for the first time rotation, stable stratification and shear, and discuss the impact of this new prescription on stellar evolution.