K-shell dielectronic resonances in photoabsorption: Differential oscillator strengths for Li-like

Recently x-ray photoabsorption in KLL resonances of O VI was predicted @A. K. Pradhan, Astrophys. J. Lett. 545, L165 ~2000!#, and detected by the Chandra X-Xay Observatory @J. C. Lee et al., Astrophys. J. Lett. ~to be published!#. The required resonance oscillator strengths f̄ r are evaluated in terms of the differential oscillator strength d f /de that relates bound and continuum absorption. We present the f̄ r values from radiatively damped and undamped photoionization cross sections for Li-like C, O, and Fe calculated using relativistic the close-coupling Breit-Pauli R-matrix method. The KLL resonances of interest here are 1s2p(P)2s @P1/2,3/2 o ,P1/2,3/2 o # and 1s2p(P)2s @P1/2,3/2 o # . The KLL photoabsorption resonances in Fe XXIV are fully resolved up to natural autoionization profiles. It is demonstrated that the undamped f̄ r independently yield the resonance radiative decay rates, and thereby provide a precise check on the resolution of photoionization calculations in general. The predicted photoabsorption features should be detectable by the x-ray space observatories and enable column densities in highly ionized astrophysical plasmas to be determined from the calculated f̄ r . The dielectronic satellites may appear as redward broadening of resonance lines in emission and absorption.