Does Iron occur in the Solar Corona?

Abstract

PROF. RUBINOWICZ has somewhat overstated my point of view in suggesting that a provisional identification of two forbidden lines of N II in the coronal spectrum proved the occurrence of nitrogen in the corona. He carefully safeguards himself from any claim that a suggested identification of one forbidden line of Fe II proves the presence of iron. But the case for iron is actually stronger than he has stated. The missing line, λ 4416·28, to which he refers, is a forbidden transition between two levels in the same electronic configuration ; and a search by Dr. Dobbie and myself of the more likely transitions of this class, which might give lines in the region of spectrum available for study, has indeed failed to show any coronal lines. On the other hand, Prof. Tanaka's list of coronal lines¹ does show coincidences with two forbidden Fe II lines, λ 4244·0, a ⁴F_4½ – a ⁴G_5½, and λ 5072·4, a ⁴F_4½ – a ⁴H_4½, these lines, like Prof. Sekiguti's line λ 4814·5, a ⁴F_4½ – b ⁴F_4½, all represent transitions from levels in the d⁶s configuration to the lowest level of the d⁷ configuration. The suggestion is that the conditions at this eclipse were favourable for the emission of forbidden lines of Fe II caused by transitions between two different electronic configurations; in such cases the transition probabilities for electric quadrupole radiation would be much higher than for magnetic dipole radiation.