Plasma environment effects on K lines of astrophysical interest. V. Universal formulae for ionization potential and K-threshold shifts

TL;DR

This paper calculates plasma effects on ionization potentials and K-thresholds for various ions, providing universal formulae to predict these shifts across different plasma conditions, aiding astrophysical modeling.

Contribution

It introduces improved universal formulae for plasma-induced ionization potential and K-threshold shifts applicable to multiple ions, extending previous models.

Findings

Modified ionization potentials and K-threshold energies are reported for specified plasma conditions.

Universal fitting formulae are improved for predicting plasma effects on ions.

Accuracy of the formulae may decrease under extreme plasma conditions with high screening parameters.

Abstract

Aims. We calculate the plasma environment effects on the ionization potentials (IPs) and K-thresholds used in the modeling of K lines for all the ions belonging to the isonuclear sequences of abundant elements apart from oxygen and iron, namely: carbon, silicon, calcium, chromium, and nickel. These calculations are used to extend the data points for the fits of the universal formulae, first proposed in our fourth paper of this series, to predict the IP and K-threshold lowerings in any elemental ion. Methods. We used the fully relativistic multi-configuration Dirac-Fock (MCDF) method and approximated the plasma electron-nucleus and electron-electron screenings with a time-averaged Debye-Huckel potential. Results. We report the modified ionization potentials and K-threshold energies for plasmas characterized by electron temperatures and densities in the ranges of 10^5-10^7 K and 10^18-10^22 cm^-3 . In addition, the improved universal fitting formulae are obtained. Conclusions. We conclude that since explicit calculations of the atomic structures for each ion of each element under different plasma conditions is impractical, the use of these universal formulae for predicting the IP and K-threshold lowerings in plasma modeling codes is still recommended. However, their comparatively moderate to low accuracies may affect the predicted opacities with regard to certain cases under extreme plasma conditions that are characterized by a plasma screening parameter of \mu > 0.2 a.u., especially for the K-thresholds.