= Jelle S. Kaastra
{c}
<Jelle S. Kaastra> develops the physical interpretation of <X-ray> <radiation spectra> from hot astronomical <plasma>. His review with collaborators explains how <ionization equilibrium>, <spectral lines> and continuum <radiation> constrain the diffuse <gas> in <galaxy clusters> and between <galaxies>.
A spectrum acts as a diagnostic because different <ions> and transitions respond differently to <temperature> and other physical conditions. The interpretation requires an atomic model: an observed <spectral line> is evidence about the emitting <plasma>, rather than a direct reading of a single universal <temperature>.<Thermal radiation processes by Jelle S. Kaastra and others>[Abstract: ionization balance, line and continuum processes and practical X-ray diagnostics]{ref}
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