Formation of Mg II h & k lines during solar flares with different heating mechanisms
Lyndsay Fletcher
University of Glasgow
Lyndsay Fletcher (University of Glasgow)
The bulk of the radiative output during solar flares originates from the solar chromosphere, making it an important region to investigate. The Interface Region Imaging Spectrograph (IRIS) now provides high spectral, spatial and temporal resolution of a number of lines, including the strong, optically thick Mg II h & k lines that are formed in the chromosphere. In order to understand the formation of these lines we model these lines using the radiative hydrodynamic code RADYN to simulate the flaring atmosphere, and the radiative transfer code RH to produce synthetic Mg II profiles from that model atmosphere. We find that the simulations qualitatively match observations, with significantly enhanced, broadened lines, that appear doppler shifted, and have asymmetries. The lines remain optically thick during the flare (as observations suggest) but condensations result in some optically thin emission from the red wing. While the central reversal (a ubiquitous in the quiet Sun) is not present in flare observations, the synthetic profiles are not always single peaked. We comment also on initial results on flare simulations in which flare heating resulted from Alfven wave dissipation as opposed to an electron beam (e.g Reep and Russell, 2016), and how this different heating mechanism affects line formation.