Far-ultraviolet Space Telescope Imaging spectrograph spectra of the white dwarf REJ 1032+532. II. Stellar spectrum

We discuss the Nubble Space Telescope Space Telescope Imaging Spectrograph UV echelle spectrum of the hot DA white dwarf REJ 1032+532. The interstella r data from this spectrum are presented by Holberg and coworkers. In this p aper we discuss a number of strong photospheric features due to C, N, and S i that are present in the REJ 1032+532 spectrum. While the inferred heavy e lement content of REJ 1032+532 roughly matches the predictions of radiative levitation for carbon and silicon, the observed nitrogen abundance greatly exceeds predictions by a factor of 50. The observed shapes of the N v line s provide the first evidence, at UV wavelengths, of heavy element stratific ation in a hot DA while dwarf. Homogeneous models are unable to reproduce t he shape of the REJ 1032+532 N v lines, nor can they account for the relati vely low degree of EUV opacity in the star. We present a simple stratified nitrogen model that resolves these problems. The high degree of stratificat ion in REJ 1032+532 is the signature of ongoing mass loss in this star. The radial velocity of REJ 1032+532 obtained with Space Telescope Imaging Spec trograph differs by 44 km s(-1) from that obtained from the Balmer H I line s with the Multiple Mirror Telescope. This suggests that REJ 1032+532 is li kely a member of a binary system containing either a late M star or another white dwarf.