Density structure of an active region and associated moss using Hinode/EIS

TL;DR

This study uses Hinode/EIS data to analyze the electron density structure of an active solar region and its moss regions, revealing how density varies with temperature and magnetic field polarity.

Contribution

It provides detailed measurements of plasma density in active regions and moss, and explores their relationship with magnetic field polarity, using multi-instrument observations.

Findings

Active region core has electron densities up to 10^10.5 cm^-3.

Moss region density peaks at log T=5.8-6.1 with 10^10-10.5 cm^-3.

Moss density correlates with positive magnetic polarity, not negative.

Abstract

Context: Studying the problem of active region heating requires precise measurements of physical plasma parameters such as electron density, temperature etc. It is also important to understand the relationship of coronal structures with the magnetic field. The Extreme-ultraviolet Imaging Spectrometer (EIS) aboard Hinode provides a rare opportunity to derive electron density simultaneously at different temperatures. Aims: MethodsWe study the density structure and characterise plasma in active regions and associated moss regions. In addition we study its relationship to the photospheric magnetic field. Methods: We used data recorded by the EIS, together with magnetic field measurements from the Michelson Doppler Imager (MDI) aboard SoHO and images recorded with the Transition Region And Coronal Explorer (TRACE) and X-Ray Telescope (XRT/Hinode). Results: We find that the hot core of the active region is densest with values as high as 10^10.5 cm^-3. The electron density estimated in specific regions in the active region moss decreases with increasing temperature. The moss areas were located primarily on one side of the active region, and they map the positive polarity regions almost exactly. The density within the moss region was highest at log T=5.8-6.1, with a value around 10^(10.0-10.5) cm^-3. The moss densities were highest in the strong positive magnetic field region. However, there was no such correlation for the negative polarity areas, where there was a large sunspot.