Transition Region Abundance Measurements During Impulsive Heating Events

TL;DR

This study measures plasma composition during impulsive heating events in the solar transition region, revealing near-photospheric abundances, contrasting with the enriched low-FIP elements in coronal structures, thus linking plasma composition to heating processes.

Contribution

It provides new measurements of plasma composition during impulsive heating events, showing near-photospheric abundances, and suggests a connection between plasma composition and the nature of coronal heating.

Findings

Impulsive heating events show plasma with near-photospheric composition.

Long-lived coronal structures exhibit low-FIP element enrichment.

Plasma composition may serve as a signature of the heating process.

Abstract

It is well established that elemental abundances vary in the solar atmosphere and that this variation is organized by first ionization potential (FIP). Previous studies have shown that in the solar corona low-FIP elements, such as Fe, Si, Mg, and Ca, are generally enriched relative to high-FIP elements, such as C, N, O, Ar, and Ne. In this paper we report on measurements of plasma composition made during impulsive heating events observed at transition region temperatures with the Extreme Ultraviolet Imaging Spectrometer (EIS) on Hinode. During these events the intensities of O IV, V, and VI emission lines are enhanced relative to emission lines from Mg V, VI, and VII and Si VI and VII and indicate a composition close to that of the photosphere. Long-lived coronal fan structures, in contrast, show an enrichment of low-FIP elements. We conjecture that the plasma composition is an important signature of the coronal heating process, with impulsive heating leading to the evaporation of unfractionated material from the lower layers of the solar atmosphere and higher frequency heating leading to long-lived structures and the accumulation of low-FIP elements in the corona.