Hubble Space Telescope Ultraviolet Spectroscopy of Two Hot White Dwarfs

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.

Based on observations with the NASA/ESA Hubble Space Telescope obtained at the Space Telescope Science Institute, which is operated by the Association of Universities for Research in Astronomy, Incorporated under NASA contract NAS 5-26555.

Observations reported here have been obtained in part with the Multiple Mirror Telescope, a joint facility of the University of Arizona and Smithsonian Institution.