Transition region features observed with Hinode/EIS

TL;DR

This paper analyzes transition region features in active regions observed with Hinode/EIS, revealing temperature, density, and dynamic properties of loop footpoints and brightening events.

Contribution

It identifies and characterizes two types of transition region features, providing detailed diagnostics of their temperature, density, and dynamic behavior using Hinode/EIS data.

Findings

Loop footpoints show temperature increase along their length.

Density decreases from 3x10^9 to 1.5x10^9 cm^-3 over 20 Mm.

Brightening regions exhibit broadened line profiles and enhanced continuum emission.

Abstract

Two types of active region feature prominent at transition region temperatures are identified in Hinode/EIS data of AR 10938 taken on 2007 January 20. The footpoints of 1 MK TRACE loops are shown to emit strongly in emission lines formed at log T=5.4-5.8, allowing the temperature increase along the footpoints to be clearly seen. A density diagnostic of Mg VII yields the density in the footpoints, with one loop showing a decrease from 3x10^9 cm^-3 at the base to 1.5x10^9 cm^-3 at a projected height of 20 Mm. The second feature is a compact active region transition region brightening which is particularly intense in O V emission (log T=5.4) but also has a signature at temperatures up to log T=6.3. The Mg VII diagnostic gives a density of 4x10^10 cm^-3, and emission lines of Mg VI and Mg VII show line profiles broadened by 50 km/s and wings extending beyond 200 km/s. Continuum emission in the short wavelength band is also found to be enhanced, and is suggested to be free-bound emission from recombination onto He^+.