2016MNRAS.461.1374R

After an extensive assessment of the effective collision strengths available to model the He-like triplet of C v, N vi, O vii, Ne ix, Mg xi and Si xiii in collisionally dominated plasmas, new accurate effective collision strengths are reported for Ne ix. The uncertainty intervals of the density and temperature diagnostics due to the atomic data errors are also determined for both Maxwell-Boltzmann and κ electron-energy distributions. It is shown that these uncertainty bands limit the temperature range where the temperature line-ratio diagnostic can be applied and its effectiveness to discern the electron-energy distribution type. These findings are benchmarked with Chandra and XMM-Newton spectra of stellar coronae and with tokamak measurements.