FAR-ULTRAVIOLET SPACE TELESCOPE IMAGING SPECTROGRAPH SPECTRA OF THE WHITE DWARF REJ 1032+532. II. STELLAR SPECTRUM

摘要

We discuss the Hubble Space Telescope Space Telescope lmaging Spectrograph UV echelle spectrum of the hot DA white dwarf REJ 1032+532. The interstellar data from this spectrum are presented by Holberg and coworkers. In this paper we discuss a number of strong photospheric features due to C, N, and Si that are present in the REJ 1032+532 spectrum. While the inferred heavy element 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 lines provide the first evidence, at UV wavelengths, of heavy element stratification in a hot DA white dwarf Homogeneous models are unable to reproduce the shape of the REJ 1032+ 532 N v lines, nor can they account for the relatively low degree of EUV opacity in the star, We present a simple stratified nitrogen model that resolves these problems. The high degree of stratification 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 lmaging Spectrograph differs by 44 km s~(-1) from that obtained from the Balmer H I lines with the Multiple Mirror Telescope. This suggests that REJ 1032+532 is likely a member of a binary system containing either a late M star or another white dwarf.