Astronomy and Astrophysics – Astronomy
Scientific paper
May 2002
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2002apjs..140...67l&link_type=abstract
The Astrophysical Journal Supplement Series, Volume 140, Issue 1, pp. 67-80.
Astronomy and Astrophysics
Astronomy
70
Ism: Abundances, Ism: Clouds, Stars: Individual: Alphanumeric: G191-B2B, Ultraviolet: Ism
Scientific paper
High-resolution spectra of the hot white dwarf G191-B2B, covering the wavelength region 905-1187 Å, were obtained with the Far Ultraviolet Spectroscopic Explorer (FUSE). These data were used in conjunction with existing high-resolution Hubble Space Telescope Space Telescope Imaging Spectrograph (STIS) observations to evaluate the total H I, D I, O I, and N I column densities along the line of sight. Previous determinations of N(D I) based upon GHRS and STIS observations were controversial as a result of the saturated strength of the D I Lyα line. In the present analysis the column density of D I has been measured using only the unsaturated Lyβ and Lyγ lines observed by FUSE. A careful inspection of possible systematic uncertainties tied to the modeling of the stellar continuum or to the uncertainties in the FUSE instrumental characteristics has been performed. The column densities derived are logN(DI)=13.40+/-0.07, logN(OI)=14.86+/-0.07, and logN(NI)=13.87+/-0.07, quoted with 2 σ uncertainties. The measurement of the H I column density by profile fitting of the Lyα line has been found to be uncertain. If additional weak, hot interstellar components are added to the three detected clouds along the line of sight, the H I column density can be reduced quite significantly, even though the signal-to-noise ratio and spectral resolution at Lyα are excellent. The new estimate of N(H I) toward G191-B2B reads logN(HI)=18.18+/-0.18 (2 σ), so that the average D/H ratio on the line of sight is D/H=(1.66+0.9-0.6)×10-5 (2 σ). This work is based on data obtained for the Guaranteed Time Team by the NASA-CNES-CSA FUSE mission operated by Johns Hopkins University.
André Martial
Blair William Patrick
Chayer Pierre
Desert Jean-Michel
Ferlet Roger
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