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

R. G. Cruddace | Zendy; Michael Kowalski | Zendy; D. Yentis | Zendy; C. M. Brown | Zendy; H. Gursky | Zendy; M. A. Barstow | Zendy; Nigel Bannister | Zendy; G.W. Fraser | Zendy; J. E. Spragg | Zendy; J. Lapington | Zendy; J. A. Tandy | Zendy; B. S. Sanderson | Zendy; J. L. Culhane | Zendy; Troy W. Barbee | Zendy; Joseph F. Kordas | Zendy; W. H. Goldstein | Zendy; G. Fritz | Zendy

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

Author(s) -

R. G. Cruddace,

Michael Kowalski,

D. Yentis,

C. M. Brown,

H. Gursky,

M. A. Barstow,

Nigel Bannister,

G.W. Fraser,

J. E. Spragg,

J. Lapington,

J. A. Tandy,

B. S. Sanderson,

J. L. Culhane,

Troy W. Barbee,

Joseph F. Kordas,

W. H. Goldstein,

G. Fritz

Publication year - 2002

Publication title -

the astrophysical journal

Language(s) - English

Resource type - Journals

SCImago Journal Rank - 2.376

H-Index - 489

eISSN - 1538-4357

pISSN - 0004-637X

DOI - 10.1086/339054

Subject(s) - physics , astrophysics , ultraviolet astronomy , interstellar medium , space telescope imaging spectrograph , white dwarf , spectroscopy , spectrograph , ultraviolet , line (geometry) , spectral line , ionization , astronomy , spectral resolution , line of sight , absorption spectroscopy , hubble space telescope , stars , astronomical spectroscopy , optics , galaxy , quantum mechanics , ion , geometry , mathematics

We report a high-resolution (R=3000-4000) spectroscopic observation of the DAwhite dwarf G191-B2B in the extreme ultraviolet band 220-245 A. A low- densityionised He component is clearly present along the line-of-sight, which ifcompletely interstellar implies a He ionisation fraction considerably higherthan is typical of the local interstellar medium. However, some of thismaterial may be associated with circumstellar gas, which has been detected byanalysis of the C IV absorption line doublet in an HST STIS spectrum. A stellaratmosphere model assuming a uniform element distribution yields a best fit tothe data which includes a significant abundance of photospheric He. The99-percent confidence contour for the fit parameters excludes solutions inwhich photospheric He is absent, but this result needs to be tested usingmodels allowing abundance gradients.Comment: LATEX format: 10 pages and 3 figures: accepted for publication in the Astrophysical Journal Letter

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