High-Resolution Spectroscopy of G191-B2B in the Extreme Ultraviolet
Abstract
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.
Keywords
Cite
@article{arxiv.astro-ph/0112254,
title = {High-Resolution Spectroscopy of G191-B2B in the Extreme Ultraviolet},
author = {R. G. Cruddace and M. P. Kowalski and D. J. Yentis and C. M. Brown and H. Gursky and M. A. Barstow and N. P. Bannister and G. W. Fraser and J. E. Spragg and J. S. Lapington and J. A. Tandy and B. Sanderson and J. L. Culhane and T. W. Barbee and J. F. Kordas and W. Goldstein and G. G. Fritz},
journal= {arXiv preprint arXiv:astro-ph/0112254},
year = {2009}
}
Comments
LATEX format: 10 pages and 3 figures: accepted for publication in the Astrophysical Journal Letters