New Observations of the IR Emission Corona from the July 2, 2019 Eclipse Flight of the Airborne Infrared Spectrometer

TL;DR

This paper reports new infrared observations of the solar corona during the 2019 eclipse using AIR-Spec, including the first detection of the 1.393 μm line and improvements in instrument sensitivity and resolution.

Contribution

It presents the first detection of the 1.393 μm coronal emission line and details significant upgrades to AIR-Spec for better infrared solar corona observations.

Findings

First detection of the 1.393 μm line in the solar corona.

Probable first detections of Si XI 1.934 μm and Fe X 1.947 μm.

Confirmed detection of Fe IX and measured its intensity variation with solar radius.

Abstract

The Airborne Infrared Spectrometer (AIR-Spec) was commissioned during the 2017 total solar eclipse, when it observed five infrared coronal emission lines from a Gulfstream V (GV) research jet owned by the National Science Foundation (NSF) and operated by the National Center for Atmospheric Research (NCAR). The second AIR-Spec research flight took place during the July 2, 2019 total solar eclipse across the South Pacific. The 2019 eclipse flight resulted in seven minutes of observations, during which the instrument measured all four of its target emission lines: S XI 1.393 $\mu$m, Si X 1.431 $\mu$m, S XI 1.921 $\mu$m, and Fe IX 2.853 $\mu$m. The 1.393 $\mu$m line was detected for the first time, and probable first detections were made of Si XI 1.934 $\mu$m and Fe X 1.947 $\mu$m. The 2017 AIR-Spec detection of Fe IX was confirmed and the first observations were made of the Fe IX line intensity as a function of solar radius. Telluric absorption features were used to calibrate the wavelength mapping, instrumental broadening, and throughput of the instrument. AIR-Spec underwent significant upgrades in preparation for the 2019 eclipse observation. The thermal background was reduced by a factor of 30, providing a 5.5x improvement in signal-to-noise ratio, and the post-processed pointing stability was improved by a factor of five to $<$10 arcsec rms. In addition, two imaging artifacts were identified and resolved, improving the spectral resolution and making the 2019 data easier to interpret.