The Pattern of Magnetic Fields in Sunspots : An Observational Determination

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Abstract
The configuration of the lines of force, along a central section of a single, regular sunspot, is determined for three disk positions of the spot. To obtain the heliographic directions of the magnetic field it is necessary to measure position angles for the lines of force, as well as their inclination to the sight-line. This is done by a full analysis of the state of polarization of the Zeeman components of the Fe lines λλ 6302.5, 6265.1, in sunspot spectra obtained with the Oxford 35m telescope and 11 m spectroscope. The analysis is made by the measurement of Babinet fringes according to the method introduced by Treanor. Telescope polarization is measured and effectively eliminated by combining the results for the red and violet σ-components of the Zeeman pattern. An ambiguity, inherent in the determination of position angles by polarization methods is pointed out ; this is resolved in the present instance by general considerations, but future observations should be planned to remove this uncertainty. The magnetic field directions across the spot section show only a very limited range of inclinations to the solar radius, and do not lie in the normal plane of the central section. The directions change from day to day quite markedly, although the magnetic field strength pattern is found to be quite stable. The observed field directions do not follow the commonly accepted directions of the Evershed flow of material.

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