AAS 196th Meeting, June 2000
Session 17. Stellar Remnants
Oral, Monday, June 5, 2000, 2:00-3:30pm, Highland A/K

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[17.04] Observations of G191-B2B with the Extreme ultraviolet Opacity Rocket

K. Gunderson, E. Wilkinson, J. C. Green (University of Colorado), M. A. Barstow (University of Leicester)

The Extreme ultraviolet Opacity Rocket (EOR) is a \lambda/\Delta\lambda=2500-3000 resolution rocket-borne EUV spectrograph. EOR observed the hot DA white dwarf star G191--B2B on 27 September 1999 over a bandpass of 250--320 Åin order to identify the EUV opacity sources in G191--B2B's photosphere.

The opacity sources are believed to be metals for several reasons. 1) The EUV spectrum of G191--B2B rolls off at longer wavelengths than can be explained by pure H or H+He model atmospheres. 2) Absorption lines of higher Z species such as Fe, Ni, Si, C, N, and O have been observed at longer wavelengths. 3) Those higher Z ions have millions of electron energy level transitions at energies around those of the EUV rolloff. Unfortunately, existing data from other EUV instruments (e.g. EUVE) has been insufficient for unambiguously identifying the EUV opacity sources where they affect the emergent spectrum most because of a lack of spectral resolution at those wavelengths. However, EOR's instrumental spectral resolving power is almost a factor of ten higher than that of EUVE.

Flight results will be presented, and comparisons of the flight spectrum with self-consistent, non-LTE, stratified, and line blanketed models will be discussed.

The author(s) of this abstract have provided an email address for comments about the abstract: gunderso@casa.colorado.edu

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