Atmospheric Imaging Assembly Response Functions: Solving the Fe VIII Problems with Hinode EIS Bright Point Data

TL;DR

This study improves the understanding of AIA response functions by addressing missing spectral lines in atomic data, leading to a revised Fe VIII emissivity peak temperature and more accurate flux estimations.

Contribution

The paper identifies issues with the CHIANTI database for Fe VIII and proposes a revised response function, enhancing the accuracy of AIA temperature diagnostics.

Findings

CHIANTI is incomplete near 131 Å for Fe VIII.

The peak temperature of Fe VIII is closer to log T = 5.8.

AIA 131 Å flux can be underestimated by about 1.25 times.

Abstract

The Atmospheric Imaging Assembly (AIA) onboard the Solar Dynamics Observatory is a state-of-the-art imager with the potential to do unprecedented time-dependent multi-thermal analysis at every pixel on scales short compared to the radiative and conductive cooling times. Recent results, however, have identified missing spectral lines in the CHIANTI atomic physics data base, which is used to construct the instrument response functions. We have done differential emission measure analysis using simultaneous AIA and Hinode/EIS observations of six X-ray bright points. Our results not only support the conclusion that CHIANTI is incomplete near 131 angstroms, but more importantly, suggest that the peak temperature of the Fe VIII emissivity/response is likely to be closer to log T = 5.8 than to the current value of log T = 5.7. Using a revised emissivity/response calculation for Fe VIII, we find that the observed AIA 131-angstrom flux can be underestimated by about 1.25, which is smaller than previous comparisons.