Line Shape-Based Spectroscopic Diagnostics of Astrophysical Plasmas in the Visible, Microwave, and Radio Ranges: A Mini-Review

Plasma spectroscopy, employing the shapes of spectral lines of atoms and ions, historically started from astrophysical plasmas (thus, it was the crossing of the macro- and micro-worlds)–before finding broad applications to all kinds of laboratory plasmas intended for various important practical purposes. The present mini-review covers advances in understanding a variety of selected astrophysical plasmas achieved by the analysis of their emission or absorption in the visible, microwave, and radio ranges. It discusses the observational data and also touches upon the relevant advances in the theory of line shapes. The presentation is organized in order of the decreasing electron density
$N_{e}$
of the astrophysical objects: from white dwarfs (
$N_{e} ~\sim ~10^{17}$
cm
$^{-3}$
) to flare stars (
$N_{e} ~\sim ~10^{15}$
cm
$^{-3}$
), solar flares (
$N_{e} ~\sim ~10^{13}$
cm
$^{-3}$
), the quiet Sun (
$N_{e} ~ \sim ~10^{11}$
cm
$^{-3}$
), the H II regions (
$N_{e} ~\sim ~10^{4}$
cm
$^{-3}$
), and the recombination epoch of the early universe (
$N_{e} ~\sim ~10^{4}$
cm
$^{-3}$
).