A New Calculation of Ne IX Line Diagnostics

TL;DR

This paper presents updated atomic calculations for Ne IX that significantly improve the accuracy of line ratio diagnostics, aligning better with observations and highlighting the need for precise atomic data in high-resolution X-ray astronomy.

Contribution

It introduces fully-relativistic R-matrix calculations for Ne IX atomic rates, demonstrating their impact on line ratio predictions and observational agreement.

Findings

New atomic rates change line ratios by up to 25% at certain temperatures.

Improved line ratios better match observations of Capella and sigma^2 CrB.

Atomic rate accuracy of 25-30% is insufficient for current high-resolution X-ray spectroscopy.

Abstract

We describe the effect that new atomic calculations, including fully-relativistic R-matrix calculations of collisional excitation rates and level-specific dielectronic and radiative recombination rates, have on line ratios from the astrophysically significant ion Ne IX. The new excitation rates systematically change some predicted Ne IX line ratios by 25% at temperatures at or below the temperature of maximum emissivity (4x10^6 K), while the new recombination rates lead to systematic changes at higher temperatures. The new line ratios are shown to agree with observations of Capella and sigma^2 CrB significantly better than older line ratios, showing that 25-30% accuracy in atomic rates is inadequate for high-resolution X-ray observations from existing spectrometers.