Abstract Details


Name: Sargam Mulay
Affiliation: University of Glasgow
Conference ID: TVS202510306
Title: Behaviour of cool UV emission from molecular hydrogen in three solar flares
Authors and Co-Authors: Lyndsay Fletcher, Hugh Hudson, Nicolas Labrosse
Abstract Type: Invited by SOC
Abstract: Solar flares are energetic and explosive events which produce their signatures at all layers of the solar atmosphere. The energy deposition occurs at the lower layers, chromosphere and temperature minimum region (TMR). The plasma properties at these layers during flares could be studied using spectroscopic observations of cool lines. We have systematically investigated cool ultraviolet (UV) emission from molecular hydrogen (H2) using the Interface Region Imaging Spectrometer (IRIS), during three X-ray flares of C5.1, C9.7 and X1.0 classes on Oct. 25, 2014. Significant emission from five H2 spectral lines appeared in the flare ribbons, interpreted as photo-excitation (fluorescence) due to the absorption of UV radiation from two Si IV spectral lines. The H2 profiles were broad and consisted of two non-stationary components in red and in the blue wings of the line in addition to the stationary component. The red (blue) wing components showed small red-shifts (blue-shifts) of ∼5–15 km/s (∼5–10 km/s). The nonthermal velocities were found to be ∼10–25 km/s. The interrelation between intensities of H2 lines and their branching ratios confirmed that H2 emission formed under optically thin plasma conditions. There is a strong spatial and temporal correlation between Si IV and H2 emission, but the H2 emission is more extended and diffuse, further suggesting H2 fluorescence, and - by analogy with flare “back-warming”- providing a means to estimate the depth from which the H2 emission originates. We find that this is 1871±157 km and 1207±112 km below the source of the Si IV emission, in two different ribbon locations.