## 3. The transport processes: rotational mixing and microscopic diffusionWe calculate the destruction of lithium in F-type stars, assuming that rotational mixing is the only source of transport for angular momentum. The evolution of the interior radial differential rotation is calculated completely self-consistently, using the most complete description currently available for the following physical processes: -
the advection of angular momentum by the meridional flow driven by the thermal imbalance in a rotating star, assuming that the rotation velocity is homogenized on isobars by anisotropic shear turbulence, as described by Zahn (1992); -
the turbulent transport due to the vertical shear present in differentially rotating bodies, including the weakening effect of the thermal diffusivity on the density stratification (for details see e.g. Talon & Zahn 1997).
The complete equation for the transport of angular momentum is then where we use standard notations for the radius where where Microscopic diffusion of lithium, helium and metals, including gravitational and thermal settling, is taken into account (see Appendix for a description of the corresponding input physics). Modeling the combination of the advective transport by the circulation and the strong horizontal diffusion present in stratified media by an effective diffusivity (cf. Chaboyer & Zahn 1992): the evolution of a chemical concentration is given by: where is the nuclear production/destruction rate and is the microscopic diffusion; we assume . The weakest point is this model is the magnitude of the horizontal diffusion coefficient. Here, we will use a parametric relation which links that coefficient to the advection of momentum: where is an unknown parameter of order unity (see Zahn 1992 for more details). © European Southern Observatory (ESO) 1998 Online publication: June 26, 1998 |