The spectral content of SDO/AIA 1600 and 1700 \AA\ filters from flare and plage observations

TL;DR

This study determines the spectral contributions to AIA 1600 and 1700 Å UV images during solar flares and plages, revealing that flare emissions mainly originate from chromospheric lines, while plage emissions are dominated by photospheric continuum.

Contribution

The paper provides the first detailed spectral analysis of AIA UV images, quantifying the chromospheric and photospheric contributions during solar activity.

Findings

AIA 1600 Å flare excess is dominated by C IV doublet and Si I continua.

AIA 1700 Å flare excess mainly comes from C I multiplet and He II lines.

Flare emissions are chromospheric, while plage emissions are photospheric.

Abstract

The strong enhancement of the ultraviolet emission during solar flares is usually taken as an indication of plasma heating in the lower solar atmosphere caused by the deposition of the energy released during these events. Images taken with broadband ultraviolet filters by the {\em Transition Region and Coronal Explorer} (TRACE) and {\em Atmospheric Imaging Assembly} (AIA 1600 and 1700~\AA) have revealed the morphology and evolution of flare ribbons in great detail. However, the spectral content of these images is still largely unknown. Without the knowledge of the spectral contribution to these UV filters, the use of these rich imaging datasets is severely limited. Aiming to solve this issue, we estimate the spectral contributions of the AIA UV flare and plage images using high-resolution spectra in the range 1300 to 1900~\AA\ from the Skylab NRL SO82B spectrograph. We find that the flare excess emission in AIA 1600~\AA\ is { dominated by} the \ion{C}{4} 1550~\AA\ doublet (26\%), \ion{Si}{1} continua (20\%), with smaller contributions from many other chromospheric lines such as \ion{C}{1} 1561 and 1656~\AA\ multiplets, \ion{He}{2} 1640~\AA, \ion{Si}{2} 1526 and 1533~\AA. For the AIA 1700~\AA\ band, \ion{C}{1} 1656~\AA\ multiplet is the main contributor (38\%), followed by \ion{He}{2} 1640 (17\%), and accompanied by a multitude of other, { weaker} chromospheric lines, with minimal contribution from the continuum. Our results can be generalized to state that the AIA UV flare excess emission is of chromospheric origin, while plage emission is dominated by photospheric continuum emission in both channels.