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.