Quiet-Sun and Coronal Hole in \ion{Mg}{2}~k line as observed by IRIS

TL;DR

This study uses IRIS extsc{Mg} II k line observations to compare quiet Sun and coronal hole chromospheric emissions, revealing significant differences linked to magnetic fields and spectral resolution, impacting solar modeling.

Contribution

It provides new insights into chromospheric differences between QS and CH using extsc{Mg} II lines, highlighting the effects of magnetic fields and spectral resolution.

Findings

Mg II k3 and k2v emissions are lower in CH than QS at similar magnetic fields

Wing emissions show no difference between QS and CH

Spectral resolution affects the observed intensity differences

Abstract

Coronal holes (CHs) regions are dark in comparison to the quiet-Sun (QS) at the coronal temperatures. However, at chromospheric and transition region (TR) temperatures, QS and CHs are hardly distinguishable. In this study we have used the \ion{Mg}{2}~2796.35~{\AA} spectral line recorded by the Interface Region Imaging Spectrometer (IRIS) to understand the similarities and differences in the QS and CH at chromospheric levels. Our analysis reveals that the emission from \ion{Mg}{2}~k3 \& k2v that originates in the chromosphere is significantly lower in CH than in QS for the regions with similar magnetic field strength. The wing emissions of \ion{Mg}{2}~k that originates from the photospheric layer, however, do not show any difference between QS and CH. The difference in \ion{Mg}{2}~k3 intensities between QS and CH increases with increasing magnetic field strength. We further studied the effects of spectral resolution on these differences and found that the difference in the intensities decreases with decreasing spectral resolution. For a resolution of 11~{\AA}, the difference completely disappears. These findings are not only important for mass and energy supply from the chromosphere to the corona but also provides essential ingredients for the modelling of the solar spectral irradiance for the understanding of the Sun-climate relationships.