ON THE INFLUENCE OF THE CONVECTIVE EFFICIENCY ON THE DETERMINATION OF THE ATMOSPHERIC PARAMETERS OF DA WHITE-DWARFS

We present a detailed calculation of model atmospheres for DA white dwarfs where several versions of the mixing-length theory, with different associated convective efficiencies, are used. The predicted emergent fluxes, color indices, and equivalent widths are most sensitive to the assumed parameterization of the theory in the range T(eff) approximately 8000-15,000 K. This, it turns out, is also the region where the Balmer jump is a most useful gravity discriminant. We discuss the implications of our calculations for previous determinations of atmospheric parameters of DA white dwarfs, and show that these results are much more model-dependent than previously believed.