  We present improved calculations for the Stark broadening of hydrogen lines
in dense plasmas typical of white dwarf atmospheres. Our new model is based on
the unified theory of Stark broadening from Vidal, Cooper, & Smith. For the
first time, we account for the non-ideal effects in a consistent way directly
inside the line profile calculations. The Hummer & Mihalas theory is used to
describe the non-ideal effects due to perturbations on the absorber from
protons and electrons. We use a truncation of the electric microfield
distribution in the quasi-static proton broadening to take into account the
fact that high electric microfields dissociate the upper state of a transition.
This approach represents a significant improvement over previous calculations
that relied on the use of an ad hoc parameter to mimic these non-ideal effects.
We obtain the first model spectra with line profiles that are consistent with
the equation of state. We revisit the properties of DA stars in the range
40,000 K > Teff > 13,000 K by analyzing the optical spectra with our improved
models. The updated atmospheric parameters are shown to differ substantially
from those published in previous studies, with a mean mass shifted by +0.034
Msun. We also show that these revised atmospheric parameters yield absolute
visual magnitudes that remain in excellent agreement with trigonometric
parallax measurements.
