Extreme ultraviolet observations of G191-B2B and the local interstellar medium with the Hopkins Ultraviolet Telescope

Details Extreme ultraviolet observations of G191-B2B and the local interstellar medium with the Hopkins Ultraviolet Telescope Extreme ultraviolet observations of G191-B2B and the local interstellar medium with the Hopkins Ultraviolet Telescope

Feb 1993

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1993apj...404..663k&link_type=abstract

Astrophysical Journal, Part 1 (ISSN 0004-637X), vol. 404, no. 2, p. 663-672.

Astronomy and Astrophysics

Astronomy

42

Extreme Ultraviolet Radiation, Interstellar Matter, Solar Neighborhood, Ultraviolet Absorption, Ultraviolet Spectra, White Dwarf Stars, Ultraviolet Astronomy, Ultraviolet Telescopes

Scientific paper

During 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.

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