HEAD Division Meeting 1999, April 1999
Session 9. Stellar Coronae
Poster, Monday, April 12, 1999, 8:30am-6:10pm, Gold Room

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[9.07] Quasi-Continuum Line Emission from Fe VII--X in the Extreme Ultraviolet Region below 120 \AA

P. Beiersdorfer (LLNL), J.K. Lepson (SSL), G.V. Brown, D.A. Liedahl, C.W. Mauche, S.B. Utter (LLNL), S.M. Kahn (Columbia)

The line emission of Fe {\sc vii} through Fe {\sc x} ions in the extreme ultraviolet region below 140 Å\ has been measured in controlled laboratory experiments under conditions representative of stellar coronae. The observations are compared to predictions from standard spectral models. We find that the atomic data bases, including CHIANTI, which claimed to be ``essentially complete for specifying the emission spectrum at wavelengths greater than 50 Å,'' are woefully incomplete and do not adequately reproduce the wealth of observed lines of the type 3\ell - n\ell'. While some of these lines missing from the models form isolated features, most msising lines are unresolved and add to form a quasi-continuum in the 60--120 Å\ region. This incompleteness can explain the poor fit of short-wavelength data from cool stars, such as \alpha-Cen, measured by the Extreme Ultraviolet Explorer satellite, the origin of which has been a source of controversy since the original observations were made. Additional laboratory measurements are being carried out involving the emission from the higher charge states of iron. The measured spectra are guiding the development of improved atomic data sets and will serve as a laboratory benchmark for comparison with the data collected as part of the X-ray Emission Line Project (XELP) that will be carried out during the first phase of the upcoming Chandra X-ray Observatory mission.\\

This work was supported by the National Aeronautics and Space Administration Optical, UV, and Gravitational Research and Analysis Program under grant NAG5-6731 and performed under the auspices of the Department of Energy by Lawrence Livermore National Laboratory under contract W-7405-ENG-48.

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