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N. Lehner (JHU), C. Gry (ESA), E.B. Jenkins (Princeton), S. Lacour, H.W. Moos (JHU), K.R. Sembach (STScI)
We use the Far Ultraviolet Spectroscopic Explorer (FUSE) PI team database (programs P104 and P204) of white dwarf stars to constrain the origin of the partial ionization observed in the local interstellar medium (LISM). With a moderate spectral resolution, FUSE provides access to several important resonance lines for such study, in particular, C II, C III, O I, N I, N II, N III, and Ar I. Ratios of Ar I and N I to H I or O I give a direct measurement of the degree of ionization because these elements remain essentially in the gas phase. When saturation effects are small, the C III/C II ratio provides key information on the LISM ionization since the ionization potential of C III is > 24.4 eV similar to He II. Previous works on 5 sightlines (Jenkins et al. 2000, ApJ, 538, L81; Lehner et al. 2002, ApJS, May, in press) show significantly subsolar abundances of Ar I and N I (relative to H I) and favor the the LISM ionization being maintained by a strong extreme ultraviolet flux rather than an incomplete recombination of helium from a previous episode of collisional ionization at high temperatures. Our survey will increase the number of sightlines by a factor 3-4. This work provides a unique opportunity to understand the physics of warm interstellar gas, an important component of the interstellar gas in galaxies.
This work is based on data obtained for the Guaranteed Time Team by the NASA-CNES-CSA FUSE mission operated by the Johns Hopkins University. Financial support to U. S. participants has been provided by NASA contract NAS5-32985.
The author(s) of this abstract have provided an email address for comments about the abstract: nl@pha.jhu.edu
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Bulletin of the American Astronomical Society, 34
© 2002. The American Astronomical Soceity.