Intensity Ratios between the 2s21S0–2s2p3P1and 2s2p1P1–2p21D2Transitions in Be‐like Ions as Electron Temperature Indicators for Solar Upper Atmosphere Plasmas

Abstract

We investigate the relative intensities of the two moderately bright Be-like 2s2 1S0-2s2p 3P1 and 2s2p 1P1-2p2 1D2 lines as a function of electron temperature. We show that the intensity ratios of the lines in the beryllium isoelectronic sequence from C III to Ni XXV ions can serve as sensitive temperature indicators for a large variety of solar plasmas. While the C III-Ne VII lines can be used to diagnose unresolved fine structures in relatively cold solar atmosphere plasmas [(1-5) × 105 K], the Na VIII-Ar XV ions can be used to diagnose coronal plasmas [(0.8-3) × 106 K], and Ca XVII-Ni XXV lines are useful to measure the temperature in flaring plasmas [(5-16) × 107 K]. We investigate the effects on the temperature determination caused by varying the number of energy levels that are included in the atomic model for the considered ions. It is found that a model that includes the 2l2l' and 2l3l' configurations is sufficient for adequately describing the relevant level populations of the Be-like ions in coronal conditions. We compare theoretical ratios obtained using collisional cross section and transition probability values derived by different theoretical methods. The atomic data are obtained from the CHIANTI database, the Hebrew University Lawrence Livermore Atomic Code (HULLAC) suite of programs, and other available sources in the literature. Finally, we use spectra of an apparently isothermal coronal plasma observed by the Solar Ultraviolet Measurement of Emitted Radiation instrument on the Solar and Heliospheric Observatory to determine the electron temperature of streamer plasma using the HULLAC and CHIANTI atomic data sets. The result is compared with the temperature derived in an earlier study using different methods.