Decomposing the AIA 304 A channel into its cool and hot components

Abstract

<p><em>[eng] The AIA 304 Å channel on board the Solar Dynamics Observatory (SDO) offers a unique</em></p><p><em>view of ≈ 105 K plasma emitting in the He II 304 Å line. However, when observing offlimb,</em></p><p><em>the emission of the (small) cool structures in the solar atmosphere (such as spicules,</em></p><p><em>coronal rain and prominence material) can be of the same order as the surrounding hot</em></p><p><em>coronal emission from other spectral lines included in the 304 Å passband, particularly</em></p><p><em>over active regions. In this paper, we investigate three methods based on temperature and</em></p><p><em>morphology that are able to distinguish the cool and hot emission within the 304 Å passband.</em></p><p><em>Themethods are based on the Differential Emission Measure (DEM), a linear decomposition</em></p><p><em>of the AIA response functions (RFit) and the Blind Source Separation (BSS) technique.</em></p><p><em>All three methods are found to produce satisfactory results in both quiescent and flaring</em></p><p><em>conditions, largely removing the diffuse corona and leading to images with cool material</em></p><p><em>off-limb in sharp contrast with the background. We compare our results with co-aligned</em></p><p><em>data from the Interface Region Imaging Spectrograph (IRIS) in the SJI 1400 Å and 2796 Å</em></p><p><em>channels, and find the RFit method to best match the quantity and evolution of the cool</em></p><p><em>material detected with IRIS. Some differences can appear due to plasma emitting in the</em></p><p><em>log T = 5.1–5.5 temperature range, particularly during the catastrophic cooling stage prior</em></p><p><em>to rain appearance during flares. These methods are, in principle, applicable to any passband</em></p><p><em>from any instrument suffering from similar cool and hot emission ambiguity, as long as there</em></p><p><em>is good coverage of the high-temperature range.</em></p>