Modelling Mg II During Solar Flares. I. Partial Frequency Redistribution, Opacity, and Coronal Irradiation

Abstract

The Interface Region Imaging Spectrograph (IRIS) has routinely observed the flaring Mg II NUV spectrum, offering excellent diagnostic potential and a window into the location of energy deposition. A number of studies have forward modelled both the general properties of these lines and specific flare observations. Generally these have forward modelled radiation via post-processing of snapshots from hydrodynamic flare simulations through radiation transfer codes. There has, however, not been a study of how the physics included in these radiation transport codes affects the solution. A baseline setup for forward modelling MgII in flares is presented and contrasted with approaches that add or remove complexity. It is shown for Mg II: (1) PRD is still required during flare simulations despite the increased densities, (2) using full angle-dependent PRD affects the solution but takes significantly longer to process a snapshot, (3) including Mg I in NLTE results in negligible differences to the Mg II lines but does affect the NUV quasi-continuum, (4) only hydrogen and Mg II need to be included in NLTE, (5) ideally the non-equilibrium hydrogen populations, with non-thermal collisional rates, should be used rather than the statistical equilibrium populations, (6) an atom consisting of only the ground state, h & k upper levels, and continuum level is insufficient to model the resonance lines, and (7) irradiation from a hot, dense flaring transition region can affect the formation of Mg II. We discuss modifications to the RH code allowing straightforward inclusion of transition region and coronal irradiation in flares.

Accepted for publication in the Astrophysical Journal

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• The Atmospheric Response to High Nonthermal Electron Beam Fluxes in Solar Flares. II. Hydrogen Broadening Predictions for Solar Flare Observations with the Daniel K. Inouye Solar Telescope
• He I 10830 Å Dimming During Solar Flares, I. The Crucial Role of Non-Thermal Collisional Ionisations
• Solar Flare Arcade Modelling: Bridging the gap from 1D to 3D Simulations of Optically Thin Radiation
• Solar Flare Ribbon Fronts I: Constraining flare energy deposition with IRIS spectroscopy
• Modeling Mg II during Solar Flares. II. Non-equilibrium Effects
• Prospects of Detecting Non-thermal Protons in Solar Flares via Lyman Line Spectroscopy: Revisiting the Orrall-Zirker Effect
• Flare Induced Photospheric Velocity Diagnostics
• Spectral variations within solar flare ribbons
• Exploring mutual information between IRIS spectral lines. II. Calculating the most probable response in all spectral windows
• Response of SDO/HMI observables to heating of the solar atmosphere by precipitating high-energy electrons
• Formation of the Mg II h and k polarization profiles in a solar plage model and their suitability to infer magnetic fields
• Radiative Hydrodynamic Simulations of the Spectral Characteristics of Solar White-light Flares
• On the Importance of Ca II Photoionisation by the Hydrogen Lyman Transitions in Solar Flare Models
• A new view of the solar interface region from the Interface Region Imaging Spectrograph (IRIS)
• Revisiting the Spectral Features of Ellerman Bombs and UV Bursts. I. Radiative Hydrodynamic Simulations