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[12.06] An Assessment of the Fe XVIII and Fe XIX Line Ratios from the Chandra Grating Observations of Capella

P. Desai, N. S. Brickhouse, J. J. Drake, A. K. Dupree, R. J. Edgar, R. Hoogerwerf, V. Kashyap, R. K. Smith, B. J. Wargelin (Harvard-Smithsonian Center for Astrophysics), D. P. Huenemoerder (MIT Center for Space Research), D. A. Liedahl (Lawrence Livermore National Laboratory)

Multiple observations of Capella obtained between 28 August 1999 and 29 April 2002 are co-added to provide high signal-to-noise spectra useful for assessing the atomic data used in plasma spectral emission codes. We discuss here the observations of Fe XVIII and XIX line emission, comparing far ultraviolet lines from FUSE, extreme ultraviolet emission lines from EUVE and Chandra LETG, and X-ray lines from Chandra LETG and HETG. We find more than a factor of 2 discrepancy between the X-ray lines from 3d-2p and 3s-2p transitions, compared with predictions from the Astrophysical Plasma Emission Code (APEC). This discrepancy is larger than the similar pattern of discrepancy found in Fe XVII. The forbidden lines from FUSE and the strong EUV resonance lines shed additional light on the problem.

This work is supported in part by the Chandra X-ray Observatory Center (NAS8-39073).

Bulletin of the American Astronomical Society, 35#2
© 2003. The American Astronomical Soceity.