February 27, 2023 to March 2, 2023
Europe/Oslo timezone

Formation Of The Lyman Continuum During Solar Flares

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Poster Flares and Eruptions Posters


Shaun McLaughlin (Queen's University Belfast)


The Lyman Continuum (LyC; <912Å) forms at the top of the chromosphere, making it a powerful tool for probing the chromospheric plasma during solar flares. SDO/EVE has observed many LyC disk-integrated flares, though this is a largely untapped dataset (aside from Machado et al 2018). Further, SolO/SPICE also provides partial coverage of the LyC (704-790Å), whilst the upcoming Solar-C/EUVST will observe 460-1220Å. It is important, therefore, to have solid theoretical predictions of the LyC formation properties during flares for comparison with current/future observations. To understand the effects of non-thermal energy deposition during flares, we analysed LyC spectra from a set of radiation hydrodynamic flare models (RADYN). The spectral response of the LyC, and the resulting temporal evolution of the NLTE departure coefficient of hydrogen, $b_1$, and the colour temperature, $T_c$, was investigated in response to a range of non-thermal electron distributions. The LyC intensity was found to increase by 3-5.5 orders of magnitude dependent on the injected energy flux. Generally, $b_1$ decreased from $10^{2-3}$ to $10^{-1-1}$ indicating a stronger coupling to local plasma conditions, while Tc increased from 8-9kK to 10-16kK. Both optically thick and thin components of LyC were found, in agreement with recent observations. The optically thick layer formed deeper in the chromosphere during a flare compared to quiescent conditions, whereas the optically thin layers form at higher altitudes due to chromospheric evaporation in low-temperature, high-density regions propagating upwards. Our analysis paves the way for an interpretation of existing and upcoming LyC observations.

Primary author

Shaun McLaughlin (Queen's University Belfast)


Mr Aaron Monson (Queen's University Belfast) Dr Graham Kerr (NASA/GSFC) Prof. Mihalis Mathioudakis (Queen's University Belfast) Dr Paulo Simões (Center for Radio Astronomy and Astrophysics Mackenzie) Dr Ryan Milligan (Queen's University Belfast)

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