Coronagraph observations of the coronal condensation of 4 February 1962

Abstract

Climax coronagraph observations of the accessible Fe lines, as well as the CaXV λ5694 line at the time of the 1962 total eclipse, are analyzed. The spectra show that the ionization equilibrium of iron is not substantially changed in an intense coronal condensation, at least for the stages X through XV. The only exception is FeXV λ7059, for which density effects are important. The stability of the ionization distribution is explained by the dynamic nature of the Fe ionization, with ions entering on the high side (FeXVI and up) due to rapid heating and then cooling through the visible stages. Comparison of the ionization distributions inferred from radiative and collisional excitation of the iron lines shows that the excitation must be by collisions everywhere at the heights examined (less than 50 000 km). The iron abundance in the corona is found to be 10⁻⁴ that of hydrogen, but this figure would be reduced by the amount of cyclic excitation. The peak electron density in the condensation is 8 × 10⁹, and the peak value of the λ5694 line/ continuum ratio is 2.5, in good agreement with calculations by Chevalier and Lambert. The ratio of the infrared FeXIII lines is measured along the limb and found to vary with electron density as expected, the 10 747/10 798 ratio is 7 or less at densities much below 10⁹ and saturates at a value of 2 for densities above that amount.

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