The Solar Minimum Eclipse of 2019 July 2. II. The First Absolute Brightness Measurements and MHD Model Predictions of Fe x, xi, and xiv out to 3.4 R ⊙

We present the spatially resolved absolute brightness of the Fe x, Fe xi, and Fe xiv visible coronal emission lines from 1.08 to 3.4 R (circle dot), observed during the 2019 July 2 total solar eclipse (TSE). The morphology of the corona was typical of solar minimum, with a dipole field dominance showcased by large polar coronal holes and a broad equatorial streamer belt. The Fe xi line is found to be the brightest, followed by Fe x and Fe xiv (in disk B (circle dot) units). All lines had brightness variations between streamers and coronal holes, where Fe xiv exhibited the largest variation. However, Fe x remained surprisingly uniform with latitude. The Fe line brightnesses are used to infer the relative ionic abundances and line-of-sight-averaged electron temperature (T ( e )) throughout the corona, yielding values from 1.25 to 1.4 MK in coronal holes and up to 1.65 MK in the core of streamers. The line brightnesses and inferred T ( e ) values are then quantitatively compared to the Predictive Science Inc. magnetohydrodynamic model prediction for this TSE. The MHD model predicted the Fe lines rather well in general, while the forward-modeled line ratios slightly underestimated the observationally inferred T ( e ) within 5%-10% averaged over the entire corona. Larger discrepancies in the polar coronal holes may point to insufficient heating and/or other limitations in the approach. These comparisons highlight the importance of TSE observations for constraining models of the corona and solar wind formation.

Automated summary

In this study, we present the spatial distribution of the brightness of the Fe x, Fe xi, and Fe xiv visible coronal emission lines observed during the total solar eclipse on July 2, 2019. By comparing the observed line brightnesses and inferred electron temperature with the Predictive Science Inc. magnetohydrodynamic model, we find that the model predicts the Fe lines rather well, but slightly underestimates the electron temperature.