Dissipation efficiency in turbulent convective zones in low-mass stars

Abstract

We extend the analysis of Penev etal. to calculate effective viscosities for the surface convective zones of three main-sequence stars of 0.775 M ⊙, 0.85 M ⊙, and the present day Sun. In addition, we also pay careful attention to all normalization factors and assumptions in order to derive actual numerical prescriptions for the effective viscosity as a function of the period and direction of the external shear. Our results are applicable for periods that are too long to correspond to eddies that fall within the inertial subrange of Kolmogorov scaling, but no larger than the convective turnover time, when the assumptions of the calculation break down. We find moderately anisotropic viscosity, scaling linearly with the period of the external perturbation, with its components having magnitudes between three and ten times smaller than the Zahn's prescription. © 2009. The American Astronomical Society. All rights reserved.