On the importance of Caii photoionization by the hydrogen lyman transitions in solar flare models

0548949 - ASÚ 2022 RIV GB eng J - Journal Article
Osborne, C. M. J. - Heinzel, Petr - Kašparová, Jana - Fletcher, L.
On the importance of Caii photoionization by the hydrogen lyman transitions in solar flare models.
Monthly Notices of the Royal Astronomical Society. Roč. 507, č. 2 (2021), s. 1972-1978. ISSN 0035-8711. E-ISSN 1365-2966
R&D Projects: GA ČR(CZ) GA19-09489S
Institutional support: RVO:67985815
Keywords : line profiles * radiative transfer * simulations
OECD category: Astronomy (including astrophysics,space science)
Impact factor: 5.235, year: 2021
Method of publishing: Open access

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 modelled to obtain the correct interpretation of observations. Here, we investigate the importance of photoionization 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 photoionization 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 photoionization effects on the calcium lines in the two simulations presented, demonstrating the importance of considering these effects in a self-consistent way.
Permanent Link: http://hdl.handle.net/11104/0324989