Spectroscopic observations of a coronal loop: Basic physical plasma parameters along the full loop length

Abstract

Coronal loops are the basic structures of the solar transition region and corona. Understanding of the physical mechanisms behind the loop heating, plasma flows, and filling are still considered a major challenge in solar physics. The mechanism(s) should be able to supply mass to the corona from the chromosphere and to heat the plasma over 1 MK within a small distance of a few hundred kilometers from the chromosphere to the corona. This problem makes coronal loops an interesting target for detailed study. In this study, we focus on spectroscopic observations of a coronal loop observed in its full length in various spectral lines as recorded by the Extreme-ultraviolet Imaging Spectrometer on board Hinode. We derive physical plasma parameters such as electron density, temperature, pressure, column depth, and filling factors along the loop length from one footpoint to the another. The obtained parameters are used to infer whether the observed coronal loop is overdense or underdense with respect to gravitational stratification of the solar atmosphere. These new measurements of physical plasma parameters, from one footpoint to another, provide important constraints on the modeling of the mass and energy balance in coronal loops.