Non-Ideal Equation of State, Refraction and Opacities in Very Cool,   Helium-Rich White Dwarf Atmospheres
  The atmospheres of cool, helium-rich white dwarfs constitute an exotic and poorly explored physical regime of stellar atmospheres. Under physical conditions where the temperature varies from $\rm 1000K$ to $\rm 10000K$, the density can reach values as large as $\rm 2 g/cm^{3}$, and the pressure is as high as $\rm 1 Mbar$, the atmosphere is no longer an ideal gas and must be treated as a dense fluid. Helium atoms become strongly correlated and refraction effects are present. Opacity sources such as $\rm He^{-}$ free-free absorption must be calculated with a formalism that has never been applied to astrophysical opacities. These effects have been ignored in previous models of cool white dwarf atmospheres. 
P. M. Kowalski (Vanderbilt Univ, LANL), D. Saumon (LANL, Vanderbilt   Univ) and S. Mazevet (LANL)