Some Observational Features of the Solar Limb Effect

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Abstract
This paper describes an observational investigation of relative wave-length displacements between spectral lines formed at the centre of the Sun's disk and at 9 well-defined positions along the polar diameter, carried out at the Arcetri and Göttingen Observatories from 1958–60. Measurements of these shifts for 30 selected moderately-intense Fe I lines with wave-lengths ranging from λ 4389.2– λ 7780.6 A served to establish the existence of a dependency upon level of excitation (i.e. a multiplet dependency) over the whole range of disk positions to which the programme referred, viz: from cos θ = 0.97 to cos θ = 0.155. The results of additional measurements on the O I triplet and the two Ni I lines around 7780 A are briefly described. The form of the centre-limb wave-length variation found by averaging the values obtained for the 30 Fe I lines (in km/sec) agrees closely with the velocity measurements of Miss Hart (1954) but corresponds less well with other recent and reliable limb effect data. The discrepancies are ascribed mainly to turbulent velocity variations at photospheric levels.

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