X-ray He-like ion diagnostics: New computations for photoionized plasmas

In a previous article, with a new code designed for a photoionized thick hot medium using a full transfer treatment of both lines and continuum, we have studied the He-like emission of a medium photoionized by an X-ray source. We considered the influence of density, ionization parameter and column density. We stressed that photoionized media are not uniform in temperature and we showed that photoexcitation and large column densities should be considered to avoid misinterpretation of the properties of the medium. To complete the possible situations observed in photoionized plasmas, we consider here the influence of microturbulence due for instance to a velocity gradient, of different element abundances, and of different ionizing spectral distributions. All new situations are computed using the same code, but with an improved version of our He-like atomic model. We give values of the G and R ratios, the equivalent width, and the ionic column densities with a greater accuracy than previously achieved. A large microturbulence results in a decrease of the G ratios for large column densities, for which the He-triplet resonant lines are optically thick. On the contrary, the R ratio is almost independent of the dispersion velocity and the element abundances, as long as the intercombination lines are optically thin. Through two “universal diagrams” not depending on any parameter, we also present a way to determine the ionization parameter and the total column density of the emitting regions from the temperature of the observed radiative recombination continuum of a given ion and its column density.