# Plasma parameters and geometry of cool and warm active region loops

## TL;DR

This study analyzes plasma parameters and magnetic structures of 50 active-region loops in the solar corona, revealing their nearly isothermal nature, filling factors, and overpressure states, to better understand coronal heating mechanisms.

## Contribution

It combines spectroscopic analysis with magnetic field extrapolation to characterize the three-dimensional structure and plasma properties of active-region loops, providing new observational constraints.

## Key findings

- Loops are nearly isothermal along the line-of-sight.
- Filling factors range from 8% to 89%.
- Most loops are overpressured compared to RTV law predictions.

## Abstract

How the solar corona is heated to high temperatures remains an unsolved mystery in solar physics. In the present study we analyse observations of 50 whole active-region loops taken with the Extreme-ultraviolet Imaging Spectrometer (EIS) on board the Hinode satellite. Eleven loops were classified as cool (<1 MK) and 39 as warm (1-2 MK) loops. We study their plasma parameters such as densities, temperatures, filling factors, non-thermal velocities and Doppler velocities. We combine spectroscopic analysis with linear force-free magnetic-field extrapolation to derive the three-dimensional structure and positioning of the loops, their lengths and heights as well as the magnetic field strength along the loops. We use density-sensitive line pairs from Fe XII, Fe XIII, Si X and Mg VII ions to obtain electron densities by taking special care of intensity background-subtraction. The emission-measure loci method is used to obtain the loop temperatures. We find that the loops are nearly isothermal along the line-of-sight. Their filling factors are between 8% and 89%. We also compare the observed parameters with the theoretical RTV scaling law. We find that most of the loops are in an overpressure state relative to the RTV predictions. In a followup study, we will report a heating model of a parallel-cascade-based mechanism and will compare the model parameters with the loop plasma and structural parameters derived here.