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Astron. Astrophys. 334, L26-L28 (1998)

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1. Introduction

Once 1s-hole ions are created by single photoionization, with simultaneous shake-up and shake-off processes, Auger decay populates directly excited states of the residual ions. These produce UV lines (Petrini and Da Silva 1996 and Petrini and Araújo 1997). Knowledge of the importance of the secondary processes which accompany single inner-shell photoionization is an useful information for a detailed analysis of both laboratory and astrophysical plasmas. The growing availability of synchrotron-radiation sources and the discovery of soft X-ray sources in the Universe have stimulated the interest in a quantitative understanding of these processes. However, despite their importance (Åberg 1969), results are at present rather scarce. For instance, in the case of Ne, Krause and his collaborators found in the early seventies (Krause 1971, Krause et al. 1971, Carlson et al. 1971) that the direct shake-up and the KL shake-off processes represented about 8% and 13.8% of the total 1s photoionization processes, respectively. The shake-up processes in this case are dominated by 2p [FORMULA] 3p excitation, the 2p [FORMULA] 3s and the 2s [FORMULA] 3s ones being weak. For Be, Krause and Caldwell (1987a, b) reported cross sections above the K-edge where the 2s [FORMULA] 3s and the 2s [FORMULA] 2p transitions represent about 19% and 10.5% of the total 1s photoionization cross section respectively.

Recently, Badnell et al. (1997) performed for boron a complex calculation of the direct and conjugate shake-up cross sections for transitions 2p [FORMULA] 3p, 3s and 2s [FORMULA] 2p, 3s, in the photon energy interval 17-45 Ry, in a close-coupling approximation using the R-matrix method and found that the total cross section for these secondary processes represents about [FORMULA] of the single 1s photoionization cross section. Furthermore, they highlighted the importance of the 2s [FORMULA] 3s shake-up excitation which dominates 2p [FORMULA] 3p and found a conjugate shake-up 2s [FORMULA] 2p transition broadly comparable with the 2p [FORMULA] 3p one. In this note we report the results of a similar calculation to that of Badnell et al. (1997) but extended to the case of CII, NIII, OIV, FV and NeVI ions. We were particularly interested on the behavior of the total shake-up cross section as function of Z and on the contribution of direct and conjugate shake-up excitations.

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© European Southern Observatory (ESO) 1998

Online publication: May 12, 1998