Geometrical and chemical dependence of K-shell X-ray features

We review and discuss the chemical and geometrical dependence of iron K features (emission line and absorption edge), and of fluorescent lines from other elements, emitted by neutral, externally X-ray-illuminated matter. Our aim is to provide simple, practical tools which could be useful for observers in order to estimate parameters easily from measured quantities. The dependence of the iron fluorescent line on the iron and oxygen abundances is explored in detail, and simple analytical formulae are given for both the Morrison & McCammon and Anders & Grevesse abundances. In the latter case, the variation of the depth of the iron K edge with the iron abundance is also shown. Fluorescent line intensities from other elements, from oxygen to nickel, are also given as a function of the inclination angle and chemical abundances. The effects of the presence of a hot corona above the cold matter on the iron line and edge are discussed. We also discuss the spectral signature of resonant transitions occurring in the hot corona itself. The present calculations are relevant to AGN and Galactic X-ray binaries, in particular black hole candidates and cataclysmic variables.