Modelling Ion Populations in Astrophysical Plasmas: Carbon in the Solar Transition Region. (arXiv:1901.08992v1 [astro-ph.SR])
<a href="http://arxiv.org/find/astro-ph/1/au:+Dufresne_R/0/1/0/all/0/1">R.P. Dufresne</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Zanna_G/0/1/0/all/0/1">G. Del Zanna</a>

A collisional-radiative model for carbon has been developed to determine ion
populations in lower-temperature, higher-density plasmas, such as the solar
transition region. These conditions mean the often-used coronal approximation
no longer holds for the modelling. The most up-to-date atomic rates have been
employed for the processes which influence the populations in these regions. In
the absence of level-resolved rates for electron-impact direct ionisation and
excitation-autoionisation, new calculations have been made using atomic codes.
Comparison with laboratory cross-sections and previous studies, where
available, show satisfactory agreement. The ion populations resulting from the
modelling are presented, demonstrating the influence each atomic process has as
density and temperature vary. An initial investigation into the influence of
photo-ionisation has also been investigated. Tests against observations have
been made by comparing the ratio of predicted to observed intensities using
differential emission measure modelling in the quiet-Sun transition region,
showing noticeable improvements and particularly for the anomalous ion, C IV.

A collisional-radiative model for carbon has been developed to determine ion
populations in lower-temperature, higher-density plasmas, such as the solar
transition region. These conditions mean the often-used coronal approximation
no longer holds for the modelling. The most up-to-date atomic rates have been
employed for the processes which influence the populations in these regions. In
the absence of level-resolved rates for electron-impact direct ionisation and
excitation-autoionisation, new calculations have been made using atomic codes.
Comparison with laboratory cross-sections and previous studies, where
available, show satisfactory agreement. The ion populations resulting from the
modelling are presented, demonstrating the influence each atomic process has as
density and temperature vary. An initial investigation into the influence of
photo-ionisation has also been investigated. Tests against observations have
been made by comparing the ratio of predicted to observed intensities using
differential emission measure modelling in the quiet-Sun transition region,
showing noticeable improvements and particularly for the anomalous ion, C IV.

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