For the first time, thanks to the new generation of X-ray satellites, Chandra and XMM-Newton, the diagnostics based on the line ratios of He-like ions could be used for powerful extra-solar plasma diagnostics (Warm Absorber in AGNs, stellar coronae, ...). These diagnostics are one of the keys for a better understanding of the solar-stellar connection: heating of the coronae, magnetic activity, etc. In this work, we have calculated the line ratio R and G which allow, respectively, electron density and temperature diagnostics. These calculations are based partly on the previous work of Porquet & Dubau (2000) and on different improvements of atomic data (see Sect. 4).
We have tabulated the results adapted for the different spectral resolutions of the spectrometers on board of Chandra and XMM-Newton for parameter ranges which correspond as much as possible to most cases of stellar coronae (hot-late type star, O B stars...).
Acknowledgements
The Space Research Organization Netherlands (SRON) is supported financially by NWO.
Copyright ESO 2001