Hinode/EIS spectroscopic validation of very hot plasma imaged with Solar Dynamics Observatory in non-flaring active region cores

TL;DR

This study demonstrates that AIA imaging can effectively identify hot coronal plasma (>5MK) in active regions by validating with Hinode/EIS spectral data, enabling high-resolution tracking of hot plasma features.

Contribution

The paper validates the use of AIA imaging for diagnosing hot plasma in active regions through direct comparison with Hinode/EIS spectral measurements, especially using CaXVII emission.

Findings

CaXVII emission correlates with bright features in AIA 94A and 335A channels.

AIA imaging can reliably track hot plasma (6-8MK) in active regions.

Hot plasma regions are limited and identifiable with specific AIA channels.

Abstract

We use coronal imaging observations with SDO/AIA, and Hinode/EIS spectral data, to explore the potential of narrow band EUV imaging data for diagnosing the presence of hot (T >~5MK) coronal plasma in active regions. We analyze observations of two active regions (AR 11281, AR 11289) with simultaneous AIA imaging, and EIS spectral data, including the CaXVII line (at 192.8A) which is one of the few lines in the EIS spectral bands sensitive to hot coronal plasma even outside flares. After careful coalignment of the imaging and spectral data, we compare the morphology in a 3 color image combining the 171, 335, and 94A AIA spectral bands, with the image obtained for CaXVII emission from the analysis of EIS spectra. We find that in the selected active regions the CaXVII emission is strong only in very limited areas, showing striking similarities with the features bright in the 94A (and 335A) AIA channels and weak in the 171A band. We conclude that AIA imaging observations of the solar corona can be used to track hot plasma (6-8MK), and so to study its spatial variability and temporal evolution at high spatial and temporal resolution.