Study of level-specific photoionization and electron-ion recombination of Ca~XVIII - Ca~~XX using unified method

Study of characteristic features of the inverse process of electron-ion

recombination and photoionization of Ca~XVIII-Ca XX obtained using the

unified method will be presented. The unified method which implements

relativistic Breit-Pauli R-matrix method and close-coupling approximation

has been used to obtain (i) level-specific and total electron-ion

recombination rate coefficients ($\alpha_{RC}(T)$)  with temperaure

that include both the radiative and dielectronic recombination (RR and

DR) in a unified manner for 98 fine structure levels of Ca XVIII with

1/2 $\leq J \leq$ 17/2 and 193 levels of Ca XIX with $0 \leq J \leq 10$

of $n \leq 10$ and $0 \leq l \leq 9$, ii) total recombination spectrum

with photoelectron energy and (iii) self-consistent sets of data for

photoionization and electron-ion recombination. Important features for

level-specific photoionization cross sections and recombination rate

coefficients ($\alpha_R$), such as for diagnostic w, x, y, z X-ray

lines in the ultraviolet region of astrophysical spectra, will be

illustrated. While monochromatic decrease are seen at the low energy

and low temperature regions, high energy region is dominated by

strong high peak resonances of photoionization and impact the

recombination rates at high temperatures, and form a DR bump for the

total recombination rates. Results show that dominance of resonances

goes down beyond the core ion excitations of n=2 states due to

convergence.