The Abundance of Iron in the Solar Corona

A comparison of the observed intensities of lines within Fe X, XI, XIV and XV multiplets, in the far ultra-violet solar spectrum, enables the population of the excited level of the ground term ( N u ) to be found, relative to that of the ground level ( N g ). This factor N u / N g is needed in the determination of the abundance from the equivalent widths of forbidden emission lines in the near-visible spectrum. Hence, it has been possible to calculate the abundance of iron in the solar corona. The value obtained is log N (Fe)/ N (H) = −4.30. This is in accordance with other coronal estimates, but is an order of magnitude greater than the value from photospheric determinations. The values of N u / N g have also been used in combination with theoretical excitation cross-sections, to calculate the electron density, N e .