The Böhm-Vitense Gap: The Role of Turbulent Convection

"Böhm-Vitense gaps," discontinuities in the color distribution of A-F type stars along the main sequence, have traditionally been attributed to the abrupt onset of strong convection (8000 K ≥ T_eff ≥ 6400 K) in stellar atmospheres and envelopes. Using the full spectrum of turbulence model to describe convective transport (Canuto, Goldman, & Mazzitelli) both in the interior and in the atmosphere yields a very sharp transition between structures that are convective only in the surface layers and structures that show a well-developed convection also in the interior. This produces a sudden change in the T_eff of stars, around T_eff ≃ 6800 K. Using numerical simulations, we show that this feature produces a stellar depletion that is consistent with the gap at 0.33 ≲ B-V ≲ 0.38. The standard mixing-length theory does not show this behavior. Consequently, this particular gap is a "T_eff" gap and not a "color" gap. In fact, it is also present in the V-I color distribution of the Hyades stars.