Abstract

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

Simon Preval (University of Leicester)

Martin Barstow (University of Leicester), Nigel Badnell (University of Strathclyde), Jay Holberg (University of Arizona), Ivan Hubeny (University of Arizona).

Arguably, the best method for determining the effective temperature (Teff) 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 Teff>40,000K, 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 different 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 et al. (2009). Finally, the third is the metal composition of the atmosphere, whereby we use the abundances of Barstow et al. (2003b) and Preval et al. (2013), creating a total of 8 model grids. We present the preliminary results of our analysis, whereby we have determined the Teff for a small selection of white dwarfs. We plan to extend our analysis by allowing metallicity to vary in future model grids.

Mode of presentation: oral