The Solar Limb Effect: Observations of Line Contours and Line Shifts

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Abstract
The low-noise spectroscopic equipment of the Oxford Gornergrat station (3090 m), has been used to obtain solar absorption line profiles from centre to limb of the disk. The measures have been made on three Fe I lines in the λ 6300 Å region where line wavelengths may also be obtained from observations of atmospheric oxygen lines. The Fe I lines show the familiar ‘c’ shape at the disk centre and there is a well-defined progressive change in line contours from centre to limb. The three lines show similar but not identical changes. The violet asymmetry, amounting to several milliangstroms gradually disappears and there is very little, if any, asymmetry at the limb. The solar limb effect and solar redshift are obtained from the measured wavelengths by adopting the solar photospheric motions established by Plaskett, and vacuum-arc laboratory wavelengths for the lines. This procedure, followed because the disk coverage of the observations does not permit a more rigorous determination, leads to redshifts and a mean limb effect curve which can be reconciled with those obtained from the visual measurement of photographic plates, when line asymmetries are taken into account. The contour changes should give valuable additional evidence for establishing the origin of the solar redshift and limb effect: the many theories are briefly discussed in the light of the present observations.

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