Active Region Moss: Basic physical parameters and their temporal variation

TL;DR

This study analyzes the physical plasma parameters of moss regions in the solar atmosphere, revealing their temperature, density, and variability over time using spectroscopic data from multiple space observatories.

Contribution

It provides detailed measurements of electron temperature, density, and filling factors in moss regions, and links these regions to the footpoints of hot and warm solar loops.

Findings

Moss emission is strongest in Fe xii and Fe xiii lines.

Characteristic temperature of moss is log T = 6.2.

Electron densities range from 1-3×10^10 cm^-3 (Fe xii) to 2-4×10^9 cm^-3 (Fe xiii and Fe xiv).

Abstract

We present a study of the physical plasma parameters such as electron temperature, electron density, column depth and filling factors in the moss regions and their variability over a short (an hour) and a long period (5 consecutive days) of time. Primarily, we have analyzed the spectroscopic observations recorded by the Extreme-ultraviolet Imaging Spectrometer (EIS) aboard Hinode. In addition we have used supplementary observations taken from TRACE and the X-Ray Telescope (XRT). We find that the moss emission is strongest in the Fe xii and Fe xiii lines. Based on analyses using line ratios and emission measure we found that the moss region has a characteristic temperature of log T = 6.2. The electron densities measured at different locations in the moss regions using Fe xii ratios are about 1-3\times1010 cm(-3) and about 2-4\times10^9 cm^(-3) using Fe xiii and Fe xiv. The electron density substantially increases (by a factor of about 3-4 or even more in some cases) when a background subtraction was performed. The density and temperature show very small variation over time. The filling factor of the moss plasma can vary between 0.1-1 and the path length along which the emission originates is from a few 100 to a few 1000 kms long. By combining the observations recorded by TRACE, EIS and XRT, we find that the moss regions correspond to the foot-points of both hot and warm loops.