Plasma Laboratory - Weizmann Institute of Science


    author    = {Rami Doron and Ehud Behar},
abstract = {The theoretical intensities of the soft X-ray Fe 16+ lines arising from 2 l -3 l ' transitions are reexamined using a three-ion collisional-radiative model that includes the contributions to line formation of radiative recombination (RR), dielectronic recombination (DR), resonant excitation (RE), and inner-shell collisional ionization (CI), in addition to the usual contribution of collisional excitation (CE). These additional processes enhance mostly the 2 p -3 s lines and not the 2 p -3 d lines. Under coronal equilibrium conditions, in the electron temperature range of 400-600 eV where the Fe 16+ line emissivities peak, the combined effect of the additional processes is to enhance the 2 p -3 s lines at 16.78, 17.05, and 17.10 Å, by ~25%, 30%, and 55%, respectively, compared with their traditional, single-ion CE values. The weak 2 p -3 d line at 15.45 Å is also enhanced by up to 20%, while the other 2 p -3 d lines are almost unaffected. The effects of DR and RE are found to be dominant in this temperature range (400-600 eV), while that of CI is 3% at the most, and the contribution of RR is less than 1%. At lower temperatures, where the Fe 16+ /Fe 17+ abundance ratio is high, the RE effect dominates. However, as the temperature rises and the Fe 17+ abundance increases, the DR effect takes over. The newly calculated line powers can reproduce most of the often observed high values of the ( I λ17.05 + I λ17.10 )/ I λ15.01 intensity ratio. The importance of ionization and recombination processes to the line strengths also helps to explain why laboratory measurements in which CE is essentially the sole mechanism agree well with single-ion calculations but do not reproduce the astrophysically observed ratios.},
journal = {The Astrophysical Journal},
number = {1},
pages = {518},
title = {The X-Ray Spectrum of Fe16+ Revisited with a Multi-Ion Model},
url = {},
volume = {574},
year = {2002},

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