Detection of "diffuse" coronal He I 1083 during the April 8 2024 Solar Eclipse: evidence for terrestrial atmospheric scattering origin

TL;DR

This study used spectroscopic observations during the April 8, 2024 solar eclipse to investigate the origin of diffuse He I 1083 nm signals, finding evidence suggesting terrestrial atmospheric scattering rather than coronal helium as the source.

Contribution

The paper presents new eclipse spectroscopic data with the CHEESE instrument, challenging previous interpretations of coronal neutral helium presence based on eclipse measurements.

Findings

He I 1083 nm signals detected in the corona and lunar disc.

Evidence suggests terrestrial atmospheric scattering causes the diffuse He I 1083 signals.

Challenges the idea of abundant neutral helium in the solar corona.

Abstract

Strong He I 1083 nm atomic line signals have been previously measured during total solar eclipses at coronal heights above the lunar limb. This rather unexpected measurement has kindled a discussion about the hypothesized presence of significant amounts of neutral helium at coronal conditions. We performed spectroscopic observations of the He I 1083 nm spectroscopic region with the newly built CHEESE instrument during the April 8th 2024 total solar eclipse to test the presence of He I 1083 in the solar corona. We detected the He I 1083, the forbidden coronal line Fe XIII 1074.7 nm, as well as the chromospheric H I 1093.8 nm Paschen-{\gamma} line in our eclipse observations. The chromospheric He I 1083 and H I 1093.8 nm Paschen-{\gamma} lines are detected in the corona as well as on the lunar disc. Our findings point toward a non-solar origin of the He I 1083 signal during the April 8th 2024 eclipse that challenge the notion of abundant neutral helium in the solar corona inferred from eclipse observations.