New Near-infrared Coronal Lines Observed during the 2019 Total Solar Eclipse

Abstract

We report on a further analysis of the Airborne Infrared Spectrometer (AIR-Spec) observations from the 2019 July 2 total eclipse and present the identifications of three new coronal lines from Fe x, Si xi, and Si vi in AIR-Spec’s 1.87–1.99 μm band. The new lines were predicted to be observable but were not observed previously in the corona. The identifications are confirmed on the basis of observed and expected line wavelengths and radiances. The observed wavelengths are very accurate, as confirmed by neutral H and He lines measured during the same observation. The predicted wavelengths are assessed by reviewing previous experimental data used to estimate the energies of these ions. We find discrepancies with several previous measurements. A reanalysis of Solar Ultraviolet Measurement of Emitted Radiation data corrects previous measurements and provides excellent agreement with the AIR-Spec values for Si xi. AIR-Spec was developed to survey the near-infrared (NIR) coronal spectrum from above Earth’s atmosphere, a critical first step in designing future balloonborne and spaceborne instrumentation to observe coronal plasma and magnetic fields using NIR emission lines. The reported results are also of interest for ground-based observatories, as the precise measurements of line wavelength enable observers to understand the nearby telluric spectrum and determine which lines can be used from the ground.