has been presented by @2017ApJ...836...12K, using IRIS observation of Fe [ii]{} lines in flaring kernels: the authors showed how in some instances these chromospheric spectral lines were clearly composed of two distinct spectral components, one at the rest wavelength and one strongly red-shifted. However, the authors offer a fairly different interpretation than : using RADYN flare simulations [@2015ApJ...809..104A], constrained by the hard X-ray (HXR) observations obtained with [*RHESSI*]{}, they could reproduce the observed shapes of the Fe [ii]{} lines as due to concomitant effects of the energy delivered by a beam of accelerated electrons. In particular, while the low energy electrons (E $\sim$ 25 – 50 keV) in the beam are responsible for creating the evaporation and heating the chromospheric condensation – producing a strongly red-shifted line, the higher energy electrons (E $\ge$ 50 keV) can penetrate in deeper, denser layers of the chromosphere and heat them, giving rise to the enhanced stationary component. Key to understanding the flaring mechanism itself, is the fact that the relative timing, and strength, of these separate effects depends on the details of the heating input, including the hardness of the beam, and the duration of the input.

The IRIS flare studied by @2017ApJ...836...12K 