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J.B. Holberg (LPL, Univ. of Arizona), M.A. Barstow (Univ. of Leicester), F.C. Bruhweiler (Catholic Univ. of America), I. Hubeny (LASP, Goddard Space Flight Center)
We present results from echelle spectra obtained with the Space Telescope Imaging Spectrograph (STIS) of the hot DA white dwarfs, GD 659 (WD0050-332) and GD 246 (WD2309+105), which provide new information on the occurrence of heavy elements in the photospheres of these stars. In the case of GD 659, we show that the C IV, N V and Si IV resonance lines, previously observed with IUE, and thought to be interstellar or circumstellar in origin, are in fact photospheric in nature. Further, the strength of the highly excited N V lines in a star as cool as GD 659 (Teff = 35,300 K) can be explained only if the nitrogen is stratified in the stellar photosphere. Thus, GD 659 is apparently similar to REJ 1032+532 and perhaps REJ 1614-085, which also show super nitrogen abundances, and have photospheres with stratified N abundances.
The author(s) of this abstract have provided an email address for comments about the abstract: holberg@argus.lpl.arizona.edu