High-Resolution Spectroscopy of G191-B2B in the Extreme Ultraviolet

Details High-Resolution Spectroscopy of G191-B2B in the Extreme Ultraviolet High-Resolution Spectroscopy of G191-B2B in the Extreme Ultraviolet

2001-12-11

arxiv.org/abs/astro-ph/0112254v1

Astronomy and Astrophysics

Astrophysics

LATEX format: 10 pages and 3 figures: accepted for publication in the Astrophysical Journal Letters

Scientific paper

10.1086/339054

We report a high-resolution (R=3000-4000) spectroscopic observation of the DA white dwarf G191-B2B in the extreme ultraviolet band 220-245 A. A low- density ionised He component is clearly present along the line-of-sight, which if completely interstellar implies a He ionisation fraction considerably higher than is typical of the local interstellar medium. However, some of this material may be associated with circumstellar gas, which has been detected by analysis of the C IV absorption line doublet in an HST STIS spectrum. A stellar atmosphere model assuming a uniform element distribution yields a best fit to the data which includes a significant abundance of photospheric He. The 99-percent confidence contour for the fit parameters excludes solutions in which photospheric He is absent, but this result needs to be tested using models allowing abundance gradients.

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