Temperature-sensitive line ratio diagnostics based on Si satellite-to-resonance line ratios for 1s2-1snp transitions

Dielectronic satellite lines due to 1s2n′l′-1snpn′l′ (n = 3, 4) transitions in Li-like Si (Si XII) occur at 5.818 and 5.565 Å, on the long wavelength side of the He-like Si (Si XIII) 1s2-1s3p and 1s2-1s4p lines at 5.681 and 5.384 Å, respectively. They have been extensively observed with the RESIK crystal spectrometer on the Russian spacecraft CORONAS-F. As with corresponding satellites 1s2nl-1s2pnl on the long-wavelength side of the Si XIII 1s2-1s2p resonance line, there is an inverse temperature dependence of the intensity ratio of the satellites to the He-like ion lines (Isat/IHe). New atomic data are used to calculate the Si XII satellite line intensities and thus the Isat/IHe ratio. RESIK observations of the ratio in solar flares, together with temperatures from the ratio of the two GOES X-ray channels, are compared with theoretical variation of the ratio with temperature. The good agreement indicates this to be a valuable temperature diagnostic for solar flares and laboratory plasmas such as tokamaks. There are implications for similar satellites in Fe line spectra which are observed with broad-band resolution by the RHESSI solar flare mission.