= Non-LTE stellar atmosphere
{title2=$\sum_jn_jP_{ji}=n_i\sum_jP_{ij}$}
= Non-LTE atmosphere
{synonym}
When radiative rates compete with or dominate collisions, level populations need statistical equilibrium coupled to <radiative transfer>, rather than thermal population laws at the local <temperature>. Radiation from other depths can make the local radiation field differ from the <Planck function>. This changes ionization and spectral-line strengths, so a geometrically thin atmosphere may still require non-LTE abundance modelling.
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