Line Profile Studies of Coronal Active Regions in Fe xii λ195.12 Using Hinode/EIS

Abstract

Coronal active regions are studied using Hinode/EIS observations in the EUV line Fe xii λ195.12 by analyzing their line profiles from 2006 December to 2019 December. The period covers the last 2 yr of solar cycle 23 and solar cycle 24 fully. Active regions are the main source of magnetic field in the solar atmosphere, important in its heating and dynamics. Line profiles were obtained from various active regions spread across the Sun on a monthly basis from which we obtained the intensity, line width, Doppler velocity, and centroid and examined their variation during the solar cycle. The histograms of the Doppler velocity and centroid show that they behave in six different ways with respect to the position of rest wavelength. In addition, the shifts in the centroid were found to be more compared to the Doppler velocity. The variation of the line width with respect to the Doppler velocity or the centroid mostly follows a second-degree polynomial. A multicomponent line profile is simulated to explain the difference in the behavior of the Doppler velocity and the centroid with respect to the line width. We also find that the intensity and the line width of the different data sets show a global dependence on the solar cycle with a good correlation. The implications of the results for the coronal heating and dynamics are pointed out.

Spectroscopic Observations of the Solar Corona during the 2017 August 21 Total Solar Eclipse: Comparison of Spectral Line Widths and Doppler Shifts between Open and Closed Magnetic Structures

“…Despite the fact that the possible wave damping in the closed fields (e.g., Gupta et al 2019), an alternative explanation to relatively constant line widths is that the nonthermal width ξ in closed fields does not primarily arise from Alfvén waves or turbulence. In fact, a component ξ ∥ parallel to the magnetic fields is often observed in on-disk ARs (e.g., Brooks & Warren 2016;Prabhakar & Raju 2022), which cannot be simply explained by the Alfvénic waves because the perturbation is perpendicular to the local magnetic field (e.g., Shi et al 2022). For example, Asgari-Targhi et al (2014) had to introduce a parallel component ξ ∥ with the Alfvén wave turbulence model to reproduce the ξ observed by Hinode/EIS.…”