Modelling of hot optically thin plasmas

Plasma with temperatures above a million Kelvin is common in the Universe a nd exists for a large part in the intergalactic space, but is also found in a variety of discrete cosmic sources that range from optically thin to thi ck. I consider briefly the general outline of X-ray spectral modelling of h ot plasmas, in particular the optically thin model applicable to sources li ke stellar coronae, clusters of galaxies, and supernova remnants. I deal wi th the diagnostics of plasma parameters to be obtained from optically thin line and continuum X-ray spectra and give some examples of spectral simulat ions for various spectrometers on board Spectrum-XG.