Two-dimensional hydrodynamic simulations of zero-age main-sequence convective cores

Two-dimensional, fully implicit hydrodynamic simulations of the structure and motion of convective cores are made on complete zero-age main-sequence stellar models between 1.2 and 20 M-.. The calculations present a picture of hydrogen-burning convective cores where the convective speeds are tens of kilometers per second and the superadiabatic excess may be quite large at various locations in the core at any time. However, when averaged over angle, radius, and time the superadiabatic excess is only about 10(-3), although the steps to obtain this number involve some uncertainties. Convective core overshooting occurs in all models. In units of the pressure scale height at the convective core boundary, the overshooting calculated is about 0.45H(p) for models above 3 M-., and it decreases to about 0.3H(p) for lower mass models. Part of this decrease arises from the increase in the pressure scale height at the convective core boundary as the convective core boundary approaches the center of the model while the model mass becomes small. However, using the actual e-folding distance for the pressure as the unit of measure, the overshooting still shows a small decrease for lower masses.