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 Rs

Abstract

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 $R_{\odot }$, 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 $B_{\odot }$ 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 - 1.4 MK in coronal holes up to 1.65 MK in the core of streamers. The line brightnesses and inferred $T_e$ values are then quantitatively compared to the PSI 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 to 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.

19 pages, 10 figures, accepted for publication in ApJ

References in corpus (10)

• CHIANTI -- an atomic database for emission lines -- Paper XVI: Version 10, further extensions
• Solar coronal lines in the visible and infrared. A rough guide
• Closed-Field Coronal Heating Driven by Wave Turbulence
• Coronal Magnetic Field Topology From Total Solar Eclipse Observations
• Identifying the Coronal Source Regions of Solar Wind Streams from Total Solar Eclipse Observations and in situ Measurements Extending Over a Solar Cycle
• CME Induced Thermodynamic Changes in the Corona as Inferred from Fe XI and Fe XIV Emission Observations during the 2017 August 21 Total Solar Eclipse
• The Effect of Solar Wind Expansion and Non-Equilibrium Ionization on the Broadening of Coronal Emission Lines
• Ion Charge States in a Time-Dependent Wave-Turbulence-Driven Model of the Solar Wind
• New deep coronal spectra from the 2017 total solar eclipse
• The Double-Bubble CME of the 2020 December 14 Total Solar Eclipse