Plasma environment effects on K lines of astrophysical interest

IV. IPs, K thresholds, radiative rates, and Auger widths in Fe II–Fe VIII^⋆

¹ Physique Atomique et Astrophysique, Université de Mons – UMONS, 7000 Mons, Belgium
e-mail: patrick.palmeri@umons.ac.be
² Department of Physics, Western Michigan University, Kalamazoo, MI 49008, USA
³ Helmholtz Institut Jena, 07743 Jena, Germany
⁴ Theoretisch Physikalisches Institut, Friedrich Schiller Universität Jena, 07743 Jena, Germany
⁵ Cahill Center for Astronomy and Astrophysics, California Institute of Technology, Pasadena, CA 91125, USA
⁶ Dr. Karl Remeis-Observatory and Erlangen Centre for Astroparticle Physics, Sternwartstr. 7, 96049 Bamberg, Germany
⁷ NASA Goddard Space Flight Center, Code 662, Greenbelt, MD 20771, USA
⁸ IPNAS, Université de Liège, Sart Tilman, 4000 Liège, Belgium

Received: 15 June 2020
Accepted: 15 September 2020

Abstract

Aims. Within the framework of compact-object accretion disks, we calculate plasma environment effects on the atomic structure and decay parameters used in the modeling of K lines in lowly charged iron ions, namely Fe II–Fe VIII.

Methods. For this study, we used the fully relativistic multiconfiguration Dirac–Fock method approximating the plasma electron–nucleus and electron-electron screenings with a time-averaged Debye-Hückel potential.

Results. We report modified ionization potentials, K-threshold energies, wavelengths, radiative emission rates, and Auger widths for plasmas characterized by electron temperatures and densities in the ranges 10⁵ − 10⁷ K and 10¹⁸ − 10²² cm⁻³. In addition, we propose two universal fitting formulae to predict the IP and K-threshold lowerings in any elemental ion.

Conclusions. We conclude that the high-resolution X-ray spectrometers onboard the future XRISM and ATHENA space missions will be able to detect the lowering of the K edges of these Fe ions due to the extreme plasma conditions occurring in the accretion disks around compact objects.