Penetration at the base of solar convection zone

Abstract

The extent of overshoot from stellar convection zones into the adjoining stable layers has been recognized to have a nonnegligible influence on evolutionary tracks of stars. Recently, Stothers & Chin (1992) have carried out a detailed model-independent analysis of substantial body of observational data to conclude that the maximum permissible overshoot is 0.2 times the local pressure scale height. In the present work a realistic solar convection zone model is constructed by employing a nonlocal equation for the velocity of convective elements and by including dissipative effects in the calculations. The convection model approach and the analysis of linear eigenmodes are combined to estimate the penetration depths below the base of the convection zone and into the overlying solar atmosphere. It is demonstrated that for an arbitrary extent of overshoot into the underlying stable region, it may not be possible to find a combination of linear modes capable of reproducing the model convective flux profile over the overshoot layers. The acceptable overshoot distance below the base of the convection zone turns out to be ≤0.2H_p or less with a probable value of 0.1H_p, which appears to be consistent with helioseismological data.