The influence of NLTE effects in Fe I lines on an inverted atmosphere I. 6301 A and 6302 A lines formed in 1D NLTE

Abstract

Ultraviolet over-ionisation of iron atoms in the solar atmosphere leads to deviations in their level populations from the Saha-Boltzmann statistics. This causes their line profiles to form in Non-Local Thermodynamic Equilibrium (NLTE) conditions. While inverting such profiles to determine atmospheric parameters, the NLTE effects are often neglected and deviations from LTE are compensated for by tweaking other quantities. We investigate how the routinely employed LTE inversion of iron lines formed in NLTE under- or over-estimates atmospheric quantities such as temperature (T), line-of-sight velocity (v_LOS), magnetic field strength (B) and inclination (gamma) while the previous papers have focused mainly on T. We synthesize the Stokes profiles of Fe I 6301.5 A and 6302.5 A lines in both LTE and NLTE using a snapshot of a 3D MHD simulation. The profiles are then inverted in LTE. By considering the atmosphere inferred from inversion of LTE profiles to be the fiducial model, we compare atmosphere from the inversion of NLTE profiles with it. Any differences observed are attributed to NLTE effects. Neglecting the NLTE effects introduces errors in the inverted atmosphere. While the errors in T can go up to 13%, in v_LOS and B the errors can be as high as 50% or more. We find these errors to be present at all three inversion nodes. Importantly, they survive degradation from spatial averaging of the profiles. We give an overview of how the neglect of NLTE effects influences the values of T, v_LOS, B and gamma determined by inverting Fe I 6300 A line pair, as observed, e.g., by Hinode. Errors are found at the sites of granules, intergranular lanes, magnetic elements, basically in every region susceptible to NLTE effects. For an accurate determination of atmospheric quantities and their stratification, it is therefore important to take account of NLTE effects.

Includes language corrections

References in corpus (7)

• Quiet Sun internetwork magnetic fields from the inversion of Hinode measurements
• An Open Source, Massively Parallel Code for Non-LTE Synthesis and Inversion of Spectral Lines and Zeeman-induced Stokes Profiles
• Vigorous convection in a sunspot granular light bridge
• Properties of solar plage from a spatially coupled inversion of Hinode SP data
• Comparison of inversion codes for polarized line formation in MHD simulations. I. Milne-Eddington codes
• Internetwork magnetic field as revealed by 2D inversions
• Vertical magnetic field gradient in the photospheric layers of sunspots

Cited by in corpus (25)

• Waves in the lower solar atmosphere: the dawn of next-generation solar telescopes
• An observationally-constrained model of strong magnetic reconnection in the solar chromosphere. Atmospheric stratification and estimates of heating rates
• Non-LTE inversions of a confined X2.2 flare: I. Vector magnetic field in the photosphere and chromosphere
• Heating of the solar chromosphere through current dissipation
• Diagnostic capabilities of spectropolarimetric observations for understanding solar phenomena I. Zeeman-sensitive photospheric lines
• The non-LTE formation of the Fe I 6173 A line in the solar atmosphere
• Influence of NLTE effects in Fe I lines on inverted atmosphere II. 6301 A and 6302 A lines formed in 3DNLTE
• Spatially resolved spectroscopy across stellar surfaces. IV. F, G, & K-stars: Synthetic 3D spectra at hyper-high resolution
• Magnetograms underestimate even unipolar magnetic flux nearly everywhere on the solar disk
• $IRI{S}^{2+}$: A comprehensive database of stratified thermodynamic models in the low solar atmosphere
• Calibrating GONG Magnetograms with End-to-end Instrument Simulation I: Background, the GONG Instrument, and End-to-end Simulation
• GRASS II: Simulations of Potential Granulation Noise Mitigation Methods
• Spectropolarimetric Inversion in Four Dimensions with Deep Learning (SPIn4D): I. Overview, Magnetohydrodynamic Modeling, and Stokes Profile Synthesis
• Constraining the magnetic vector in the quiet solar photosphere and the impact of instrumental degradation
• Limitations of the Ca II 8542 Å line for the determination of magnetic field oscillations
• A study of the capabilities for inferring atmospheric information from high-spatial-resolution simulations
• $\text{globin}$: A spectropolarimetric inversion code for the coupled inference of atomic line parameters
• The MODEST catalog of depth-dependent spatially coupled inversions of sunspots observed by Hinode/SOT-SP
• The Effects of Sunspots on Spectral Line Shapes in the Visible
• Superstrong magnetic fields in sunspot bipolar light bridges
• Multi-height probing of horizontal flows in the solar photosphere
• A High-resolution, Inversion-Based Synoptic Study of Solar Granulation
• Three-dimensional non-LTE radiative transfer effects in Fe I lines IV. Line formation at high spatial resolution
• Formation of chromospheric Fe I lines in the near ultraviolet in 1D atmospheres
• Effects of spatial resolution on inferences of atmospheric quantities from simulations