Observation and Modeling of Coronal "Moss" With the EUV Imaging Spectrometer on Hinode

TL;DR

This study analyzes solar active region moss using Hinode's EUV spectrometer, revealing that steady loop models overestimate emission intensities unless a nonuniform filling factor is considered.

Contribution

It demonstrates that steady, uniform heating models do not match observations unless a variable filling factor is incorporated, highlighting the complexity of coronal loop heating.

Findings

Predicted intensities are too high without a filling factor.

A filling factor of about 16% aligns models with observations.

Filling factor varies inversely with loop pressure.

Abstract

Observations of transition region emission in solar active regions represent a powerful tool for determining the properties of hot coronal loops. In this Letter we present the analysis of new observations of active region moss taken with the Extreme Ultraviolet Imaging Spectrometer (EIS) on the \textit{Hinode} mission. We find that the intensities predicted by steady, uniformly heated loop models are too intense relative to the observations, consistent with previous work. To bring the model into agreement with the observations a filling factor of about 16% is required. Furthermore, our analysis indicates that the filling factor in the moss is nonuniform and varies inversely with the loop pressure.