Electron density diagnostic for hot plasmas in the coronal regime by using b-like ions

A line ratio of 3d-2p transition lines in boron-like spectra of Si x, S xii, Ar xiv, and Fexxii has been investigated. Collisional-radiative model calculations reveal that the line ratio is sensitive to the electron density in ranges of ne = 4.0 × 107-3.0 × 1010 cm−3, 4.0 × 108-3.0 × 1011 cm−3, 3.0 × 109-4.0 × 1012 cm−3, and 2.0 × 1012-3.0 × 1015 cm−3, respectively. This complements the K-shell diagnostics of helium-like ions. By a comparison between the predicted and the measured values, effective electron densities in the electron beam ion trap (EBIT) plasmas, performed by Lepson and collaborators at the Lawrence Livermore EBIT, are estimated to be ne = 3.4+0.8 −0.6 × 1010 cm−3 and 5.6+1.0 −1.1 × 1010 cm−3 for sulfur and argon plasmas, respectively. In the case of argon, a good agreement is shown with the actual electron density derived from an Nvi K-shell spectrum. We further explore the 3d-2p transition lines of Si x and S xii in the stellar coronal spectra measured with the low energy transmission grating spectrometer combined with a high resolution camera on board the Chandra X-Ray Observatory. The constrained electron densities show a good agreement with those determined from Cv and Ovii K-shell spectra.