Photoionization of Ca~XVII-XIX*

Characteristic features of photoionization of He- and Li-like Ca, Ca~XVII and Ca~XIX,`have been studied using the relativistic Breit-Pauli R-matrix method and close coupling approximation. Photoionization cross sections $\sigma_{PI}$ of both ions show monotonic decrease from threshold to high energies as the core excitations lie in the high energy. Resonances begin with K$_{\alpha}$ excitations. Rydberg series of resonances due to n=2 excitations dominate photoionization. Beyond n=2 excitations resonances
become weaker. $\sigma_{PI}$ for K$_{\alpha}$ lines due to 1s-2p transitions in the core ions are of particular interest for diagnostic modeling of high temperature plasmas. Prominent Seaton resonances due to photo-excitation of core
appear in $\sigma_{PI}$ of excited levels. Results include total photoionization cross sections of fine structure
levels with 1/2 $\leq J \leq$ 17/2, n $\leq$ 10 and 0 $\leq l \leq$ 9 of Ca~XVIII and with $0 \leq J \leq 10$, n $\leq$ 10 and 0 $\leq l \leq$ 9 of
Ca~XIX. They correspond to 98 bound levels of Ca~XVIII and 193 of Ca~XIX. The close coupling wave function expansion for Ca~XVIII included 17 levels up to n=3 thresholds and that of Ca~XIX 16 levels up to n=4 thresholds of the core ion.