A possible solution to the Lyman/Balmer line problem in hot DA white dwarfs

Arguably, the best method for determining the effective temperature (T[subscript: eff]) and surface gravity (log g) of a DA white dwarf is by fitting the Hydrogen Lyman and Balmer absorption features. However, as has been shown for white dwarfs with T[subscript: eff]>50,000K, the calculated value from the Lyman and Balmer lines are discrepant, which worsens with increasing temperature. Many different solutions have been suggested, ranging from the input physics used to calculate the models, to interstellar reddening. We will focus on the former, and consider three variables. The first is the atomic data used, namely the number of transitions included in line blanketing treatments and the photoionization cross sections. The second is the stark broadening treatment used to synthesise the Lyman and Balmer line profiles, namely the calculations performed by Lemke (1997) and Tremblay & Bergeron (2009). Finally, the third is the atmospheric content. The model grids are calculated with a pure H composition, and a metal polluted composition using the abundances of Preval et al. (2013). We present the preliminary results of our analysis, whereby we have determined the T[subscript: eff] for a small selection of white dwarfs. We plan to extend our analysis by allowing metallicity to vary in future model grids.