Chemical transport processes in stellar interiors

Sylvie Théado

In these course, I will describe the main processes which lead to transport of matter and momentum in rotating stars interiors, hence modifying the structure and the evolution of the objects. These processes are of two types:

• microscopic processes: which are selective processes leading to element segregation in stars.
• macroscopic processes: which lead to global chemical transport. Among them is the occurrence of various fluid dynamical instabilities and large scale circulations.

The purpose of the first lecture will be to examine the microscopic processes (molecular diffusion, gravitational settling, thermal diffusion and radiation pressure), to discuss the difficulties related to their modeling and to compare the observed and predicted abundance anomalies in stellar atmospheres.

The second and third lectures will be dedicated to macroscopic processes. Firstly I will review the hydrodynamical instabilities which may occur in stellar interiors (convective, Rayleigh, baroclinic, shear instabilities), I will discuss their occurrence and their consequences. In the third lecture I will describe meridional currents which are the main large scale circulations triggered in radiative interiors. I will examine the theory of these currents, their modeling and their interaction with turbulent motions.