Electron impact excitation of Be-like ions: a comparison of DARC and ICFT results

TL;DR

This paper compares two independent R-matrix calculations (DARC and ICFT) of electron impact excitation data for Be-like ions, highlighting discrepancies and analyzing their potential causes to improve plasma diagnostics accuracy.

Contribution

It provides a detailed comparison of DARC and ICFT results for Be-like ions, identifying significant differences and discussing their origins.

Findings

Large discrepancies found between DARC and ICFT collision strengths for many transitions.

Analysis suggests methodological differences contribute to discrepancies.

Highlights the need for careful selection of atomic data in plasma modeling.

Abstract

Emission lines of Be-like ions are frequently observed in astrophysical plasmas, and many are useful for density and temperature diagnostics. However, accurate atomic data for energy levels, radiative rates (A-values) and effective electron excitation collision strengths ($\Upsilon$) are required for reliable plasma modelling. In general it is reasonably straightforward to calculate energy levels and A- values to a high level of accuracy. By contrast, considerable effort is required to calculate $\Upsilon$, and hence it is not always possible to assess the accuracy of available data. Recently, two independent calculations (adopting the $R$-matrix method) but with different approaches (DARC and ICFT) have appeared for a range of Be-like ions. Therefore, in this work we compare the two sets of $\Upsilon$, highlight the large discrepancies for a significant number of transitions and suggest possible reasons for these.