Hubble Space TelescopeUltraviolet Spectroscopy of Two Hot White Dwarfs

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Abstract
We have obtained Hubble Space Telescope high-dispersion spectroscopy of two hot white dwarfs using the Goddard High-Resolution Spectrograph. The stars were selected on the basis of EUV flux as examples of H-rich DA stars containing high and low levels of short-wavelength opacity. The high-opacity star, REJ 1614-085, possesses strong features due to C IV, Si IV, and N V. Carbon and silicon in this star are underabundant with respect to the predictions of radiative levitation; nitrogen, however, is superabundant. This is in sharp contrast to the apparently similar DA star GD 394, where silicon is in extreme overabundance. The low-opacity star PG 1057+719, as expected, shows no clear evidence of these or any other heavy ions. We find evidence of weak blueshifted components in the REJ 1614-085 C IV and Si IV lines, which may indicate the star is experiencing ongoing mass loss.