EUV Spectroscopy of Hot DA White Dwarfs

The effects of trace elements on the spectra of hot DA white dwarfs are most pronounced in the extreme ultraviolet (EUV), shortward of 300 Angstroms . We have obtained EUV spectra of several DA which were observed with the Extreme Ultraviolet Explorer spectrometer, which has a resolution of lambda / delta lambda = 300 - 400, and covers the wavelength range 70 -- 760 Angstroms . We have analyzed these spectra using models which self-consistently include the opacities of trace heavy elements. We confirm the photometric result that a wide range of trace element abundances exists among the hot DA. We further find that, contrary to expectations, large abundance differences can exist even between DA which have very similar effective temperatures and gravities, as is the case for G191-B2B and GD 246.