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Published January 2022 | Accepted Version + Published
Journal Article Open

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


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 method and approximated the plasma electron-nucleus and electron-electron screenings with a time-averaged Debye–Hückel potential. Results. We report the modified ionization potentials and K-threshold energies for plasmas characterized by electron temperatures and densities in the ranges of 10⁵−10⁷ K and 10¹⁸−10²² 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 μ > 0.2 a.u., especially for the K-thresholds.

Additional Information

© ESO 2022. Received 15 June 2021; Accepted 9 October 2021. Published online 10 January 2022. J.D. is Research Fellow of the Belgian American Educational Foundation Inc. (BAEF) while P.P. and P.Q. are, respectively, Research Associate and Research Director of the Belgian Fund for Scientific Research (F.R.S.-FNRS). Financial supports from these organizations, as well as from the NASA Astrophysics Research and Analysis Program (grant 80NSSC17K0345) are gratefully acknowledged. J.A.G. acknowledges support from the Alexander von Humboldt Foundation.

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Accepted Version - 2110.09957.pdf


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August 22, 2023
October 23, 2023