From Evaporation to Condensation: Tracking the Thermal History of Flare Plasma with IRIS and SDO/AIA

Abstract:

IRIS slit-jaw images (SJIs) in the 1330 angstrom channel occasionally show diffuse features that resemble hot coronal loops observed in EUV images of the corona. IRIS FUV spectra indicate these intensity features to be due to Fe XXI emission at log T/K ~ 7. We perform differential emission measure (DEM) inversions on SDO/AIA observations of these regions and find good morphological match between Fe XXI intensity features in IRIS SJI and AIA-derived emission measure maps around log T/K ~ 7. The cooling of the flare plasma from 10 MK to 1 MK can be continuously tracked using the latter. The moment sub-MK temperatures are reached, condensations appear in IRIS Si IV SJIs. This result underlines how the combination of IRIS and AIA provides powerful diagnostics for tracking the thermal history of chromospheric and coronal plasmas.