Properties of the C II 1334 {\AA} line in Coronal Hole and Quiet Sun as observed by IRIS

TL;DR

This study uses IRIS spectroscopic data to compare the properties of the C II 1334 Å line in Coronal Holes and Quiet Sun regions, revealing differences in intensity, flows, and line profiles related to magnetic flux density.

Contribution

It provides new insights into the variations of chromospheric line properties between CH and QS at different magnetic flux levels, aiding in understanding solar atmospheric heating and wind formation.

Findings

Coronal Holes show lower intensity and narrower lines than Quiet Sun at the same magnetic flux.

CH regions exhibit excess upflows and downflows compared to QS, depending on flow direction.

Spectral profiles are more skewed and flatter than Gaussian, with no difference between CH and QS.

Abstract

Coronal Holes (CHs) have subdued intensity and net blueshifts when compared to Quiet Sun (QS) at coronal temperatures. At transition region temperatures, such differences are obtained for regions with identical photospheric absolute magnetic flux density ($\vert$B$\vert$). In this work, we use spectroscopic measurements of the \car 1334~{\AA} line from Interface Region Imaging Spectrograph (IRIS), formed at chromospheric temperatures, to investigate the intensity, Doppler shift, line width, skew, and excess kurtosis variations with $\vert$B$\vert$. We find the intensity, Doppler shift, and line widths to increase with $\vert$B$\vert$ for CHs and QS. The CHs show deficit in intensity and excess total widths over QS for regions with identical $\vert$B$\vert$. For pixels with only upflows, CHs show excess upflows over QS, while for pixels with only downflows, CHs show excess downflows over QS that cease to exist at $\vert$B$\vert$ $\le$ 40. Finally, the spectral profiles are found to be more skewed and flatter than a Gaussian, with no difference between CH and QS. These results are important in understanding the heating of the atmosphere in CH and QS, including solar wind formation, and provide further constraints on the modeling of the solar atmosphere.