X-ray powerful diagnostics for highly-ionized plasmas: He-like ions
  The calculations of the ratios of the Helium-like ion X-ray lines from C V to Si XIII are revisited in order to apply the results to density, temperature and ionization process diagnostics of data from high-resolution spectroscopy of the new generation of X-ray satellites: Chandra and XMM-Newton.   Comparing to earlier computations, Porquet & Dubau (2000), the best experimental values are used for radiative transition probabilities. The influence of an external radiation field (photo-excitation), the contribution from unresolved dielectronic satellite lines and the optical depth are taken into account.   These diagnostics could be applied to collision-dominated plasmas (e.g., stellar coronae), photo-ionized plasmas (e.g., ``Warm Absorber'' in AGNs), and transient plasmas (e.g., SNRs). 
D. Porquet (1,5), R. Mewe (2), J.S. Kaastra (2), J. Dubau (3,5),   A.J.J. Raassen (4,2) ((1) Service d'Astrophysique, CEA Sa...