Differential rotation and meridional flow for fast-rotating solar-type stars

Observations indicate that normalized surface differential rotation decreases for fast-rotating stars, that is, \Omega Delta\Omega proportional to Omega(-0.3). An increase of \Delta Omega\/Omega is provided, however, by the current Reynolds stress theory of differential rotation in stellar convection zones, without the inclusion of meridional dow. We compute both the pole-equator difference of the surface angular velocity and the meridional drift for various Taylor numbers to demonstrate that the inclusion of meridional how in the computations for fast rotation yields a systematic reduction of the resulting differential rotation. Our model's adiabatic and density-stratified convection zone, with stress-free surfaces and a thickness of 0.3 stellar radii, yields the relation \Delta Omega\/Omega proportional to Omega(-(0.15...0.30)) for stars with faster rotation than the Sun, in agreement with previous observations. If the Coriolis number rather than the Taylor number is varied, we find a maximum differential rotation of 20%. For stars with fast rotation, exponents of up to n ' similar or equal to 0.4 are found. All rotation laws exhibit superrotating equators.