Strong-line limit
= Strong-line limit
{title2=$C\gg1$}
A regime where optical-depth-one transmission occurs in the far wings of a strongly absorbing line. With a uniformly mixed absorber, $\Delta=\Delta_sp/p_s$ and $C=qSp_s/(2\pi g\Delta_s)\gg1$, the radiative-wing optical depth is $\tau\simeq qS\Delta_s p^2/[2\pi gp_s(\nu-\nu_0)^2]$. This condition does not make pressure broadening valid in the arbitrarily rarefied upper atmosphere.