Osborne, C.M.J., Heinzel, P., Kasparova, J. and Fletcher, L. (2021) On the importance of Ca II photoionisation by the hydrogen Lyman transitions in solar flare models. Monthly Notices of the Royal Astronomical Society, 507(2), pp. 1972-1978. (doi: 10.1093/mnras/stab2156)
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Abstract
The forward fitting of solar flare observations with radiation-hydrodynamic simulations is a common technique for learning about energy deposition and atmospheric evolution during these explosive events. A frequent spectral line choice for this process is Ca ii 854.2 nm due to its formation in the chromosphere and substantial variability. It is important to ensure that this line is accurately modeled to obtain the correct interpretation of observations. Here we investigate the importance of photoionisation of Ca ii to Ca iii by the hydrogen Lyman transitions; whilst the Lyman continuum is typically considered in this context in simulations, the associated bound-bound transitions are not. This investigation uses two RADYN flare simulations and reprocesses the radiative transfer using the Lightweaver framework which accounts for the overlapping of all active transitions. The Ca ii 854.2 nm line profiles are found to vary significantly due to photoionisation by the Lyman lines, showing notably different shapes and even reversed asymmetries. Finally, we investigate to what extent these effects modify the energy balance of the simulation and the implications on future radiation-hydrodynamic simulations. There is found to be a 10-15 per cent change in detailed optically thick radiative losses from considering these photoionisation effects on the calcium lines in the two simulations presented, demonstrating the importance of considering these effects in a self-consistent way.
| Item Type: | Articles |
|---|---|
| Additional Information: | C.M.J.O. acknowledges support from the UK Research and Innovation’s Science and Technology Facilities Council (STFC) doctoral training grant ST/R504750/1. P.H. and J.K. were supported by grant 19-09489S (GACR) and project RVO:67985815. L.F. acknowledges support from UK Research and Innovation’s Science and Technology Facilities Council under grant award number ST/T000422/1. |
| Status: | Published |
| Refereed: | Yes |
| Glasgow Author(s) Enlighten ID: | Fletcher, Professor Lyndsay and Osborne, Chris and Kasparova, Dr Jana |
| Authors: | Osborne, C.M.J., Heinzel, P., Kasparova, J., and Fletcher, L. |
| College/School: | College of Science and Engineering > School of Physics and Astronomy |
| Journal Name: | Monthly Notices of the Royal Astronomical Society |
| Publisher: | Oxford University Press |
| ISSN: | 0035-8711 |
| ISSN (Online): | 1365-2966 |
| Published Online: | 29 July 2021 |
| Copyright Holders: | Copyright © 2021 The Authors |
| First Published: | First published in Monthly Notices of the Royal Astronomical Society 507(2): 1972-1978 |
| Publisher Policy: | Reproduced under a Creative Commons License |
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