X-Ray Photoabsorption in KLL Resonances of O [CSC]vi[/CSC] and Abundance Analysis

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Abstract
It is shown that photoabsorption via autoionizing resonances may be appreciable and used for abundance analysis. Analogous to spectral lines, the "resonance oscillator strength" r may be defined and evaluated in terms of the differential oscillator strength df/d that relates bound and continuum absorption. X-ray photoabsorption in KLL (1s2s2p) resonances of O VI is investigated using highly resolved relativistic photoionization cross sections with fine structure. It is found that r is comparable to that for UV dipole transition in O VI (2s-2p) and the X-ray (1s2 1S0-1s2p 1P) transition in O VII. The dominant O VI (KLL) components lie at 22.05 and 21.87 Å. These predicted absorption features should be detectable by the Chandra X-Ray Observatory and the X-Ray Multimirror Mission. The combined UV/X-ray spectra of O VI/O VII should yield valuable information on the ionization structure and abundances in sources such as the "warm absorber" region of active galactic nuclei and the hot intergalactic medium. Some general implications of resonant photoabsorption are addressed.