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Extreme ultraviolet observations of G191-B2B and the local interstellar medium with the Hopkins Ultraviolet TelescopeDuring the Astro-l mission in 1990 December, the Hopkins Ultraviolet Telescope (HUT) was used to observe the extreme ultraviolet spectrum (415-912 A) of the hot DA white dwarf GI91-B2B. Absorption by neutral helium shortward of the 504 A He I absorption edge is clearly detected in the raw spectrum. Model fits to the observed spectrum require interstellar neutral helium and neutral hydrogen column densities of 1.45 +/- 0.065 x 10 exp 17/sq cm and 1.69 +/- 0.12 x 10 exp 18/sq cm, respectively. Comparison of the neutral columns yields a direct assessment of the ionization state of the local interstellar cloud surrounding the Sun. The neutral hydrogen to helium ratio of 11.6 +/- 1.0 observed by HUT strongly contradicts the widespread view that hydrogen is much more ionized than helium in the local interstellar medium, a view which has motivated some exotic theoretical explanations for the supposed high ionization.
Document ID
19930045204
Document Type
Reprint (Version printed in journal)
External Source(s)
Authors
Kimble, Randy A. (NASA Goddard Space Flight Center Greenbelt, MD, United States)
Davidsen, Arthur F. (NASA Goddard Space Flight Center Greenbelt, MD, United States)
Blair, William P. (NASA Goddard Space Flight Center Greenbelt, MD, United States)
Bowers, Charles W. (NASA Goddard Space Flight Center Greenbelt, MD, United States)
Van Dyke Dixon, W. (NASA Goddard Space Flight Center Greenbelt, MD, United States)
Durrance, Samuel T. (NASA Goddard Space Flight Center Greenbelt, MD, United States)
Feldman, Paul D. (Johns Hopkins Univ. Baltimore, MD, United States)
Ferguson, Henry C. (Cambridge Univ. Observatories, United Kingdom)
Henry, Richard C. (NASA Goddard Space Flight Center Greenbelt, MD, United States)
Kriss, Gerard A. (Johns Hopkins Univ. Baltimore, MD, United States)
Date Acquired
August 16, 2013
Publication Date
February 20, 1993
Publication Information
Publication: Astrophysical Journal, Part 1
Volume: 404
Issue: 2
ISSN: 0004-637X
Subject Category
ASTROPHYSICS
Funding Number(s)
CONTRACT_GRANT: NAS5-27000
Distribution Limits
Public
Copyright
Other