The Solar Minimum Eclipse of 2019 July 2. III. Inferring the Coronal $T_e$ with a Radiative Differential Emission Measure Inversion

Abstract

Differential Emission Measure (DEM) inversion methods use the brightness of a set of emission lines to infer the line-of-sight (LOS) distribution of the electron temperature ($T_e$) in the corona. DEM inversions have been traditionally performed with collisionally excited lines at wavelengths in the Extreme Ultraviolet (EUV) and X-ray. However, such emission is difficult to observe beyond the inner corona (1.5 R${}_{\odot }$), particularly in coronal holes. Given the importance of the $T_e$ distribution in the corona for exploring the viability of different heating processes, we introduce an analog of the DEM specifically for radiatively excited coronal emission lines, such as those observed during total solar eclipses (TSEs) and with coronagraphs. This Radiative DEM (R-DEM) inversion utilizes visible and infrared emission lines which are excited by photospheric radiation out to at least 3 R${}_{\odot }$. Specifically, we use the Fe X (637 nm), Fe XI (789 nm), and Fe XIV (530 nm) coronal emission lines observed during the 2019 July 2 TSE near solar minimum. We find that despite a large $T_e$ spread in the inner corona, the distribution converges to an almost isothermal yet bimodal distribution beyond 1.4 R${}_{\odot }$, with $T_e$ ranging from 1.1 to 1.4 in coronal holes, and from 1.4 to 1.65 MK in quiescent streamers. Application of the R-DEM inversion to the Predictive Science Inc. magnetohydrodynamic (MHD) simulation for the 2019 eclipse validates the R-DEM method and yields a similar LOS Te distribution to the eclipse data.

20 pages, 9 figures, accepted for publication in ApJ

References in corpus (13)

• CHIANTI -- an atomic database for emission lines -- Paper XVI: Version 10, further extensions
• Thermal Diagnostics with the Atmospheric Imaging Assembly onboard the Solar Dynamics Observatory: A Validated Method for Differential Emission Measure Inversions
• Closed-Field Coronal Heating Driven by Wave Turbulence
• Coronal Magnetic Field Topology From Total Solar Eclipse Observations
• The Sun's Dynamic Extended Corona Observed in Extreme Ultraviolet
• Identifying the Coronal Source Regions of Solar Wind Streams from Total Solar Eclipse Observations and in situ Measurements Extending Over a Solar Cycle
• Direct observations of a complex coronal web driving highly structured slow solar wind
• 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 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
• The Effect of Solar Wind Expansion and Non-Equilibrium Ionization on the Broadening of Coronal Emission Lines
• Slow wind belt in the quiet solar corona
• Coronal Densities, Temperatures and Abundances During the 2019 Total Solar Eclipse: The Role of Multi-Wavelength Observations in Coronal Plasma Characterization
• On the Application of Differential Evolution to the Analysis of X-Ray Spectra

Cited by in corpus (2)

• Total Solar Eclipse White Light Images as a Benchmark for PFSS Coronal Magnetic Field Models: An In-Depth Analysis over a Solar Cycle
• Evidence of Extreme Ultraviolet Resonant Excitation in the Middle Corona During A Solar Flare