New EUV Fe IX emission line identifications from Hinode/EIS

TL;DR

This paper reports the first identification of four Fe IX emission lines in the EUV spectrum from Hinode/EIS, highlighting the 197.86 A line as a key plasma diagnostic near 800,000 K, with theoretical and observed ratios confirming temperature sensitivity.

Contribution

First identification of four Fe IX lines in EUV spectra from Hinode/EIS, providing new diagnostics for plasma temperature around 800,000 K.

Findings

The 197.86 A line is unblended and near the EIS sensitivity peak.

Observed line ratios match theoretical predictions, confirming weak density and temperature sensitivity.

The derived plasma temperature is log T=5.95, close to Fe IX ionization maximum.

Abstract

Four Fe IX transitions in the wavelength range 188--198 A are identified for the first time in spectra from the EUV Imaging Spectrometer on board the Hinode satellite. In particular the emission line at 197.86 A is unblended and close to the peak of the EIS sensitivity curve, making it a valuable diagnostic of plasma at around 800,000 K - a critical temperature for studying the interface between the corona and transition region. Theoretical ratios amongst the four lines predicted from the CHIANTI database reveal weak sensitivity to density and temperature with observed values consistent with theory. The ratio of 197.86 relative to the 171.07 resonance line of Fe IX is found to be an excellent temperature diagnostic, independent of density, and the derived temperature in the analysed data set is log T=5.95, close to the predicted temperature of maximum ionization of Fe IX.