Other
Scientific paper
Jul 1986
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1986mnras.221..499s&link_type=abstract
Monthly Notices of the Royal Astronomical Society (ISSN 0035-8711), vol. 221, July 15, 1986, p. 499-511.
Other
3
Magnetic Field Configurations, Magnetic Stars, Stellar Magnetic Fields, Stellar Models, Circular Polarization, Field Strength, Weighting Functions, Zeeman Effect
Scientific paper
The classical approach to the modelling of stellar magnetic field geometries is based on the use of the integrated field measures. Correct mapping of the surface field distribution is possible only if the field measures in question are invariant to macroscopic velocity fields, insensitive to line strength and if they result from a well-defined weighting process. Having demonstrated in a previous paper that these conditions are not met by 'statistical' methods of field determination which extract the mean intensity and polarization signal from a large number of lines simultaneously, we discuss in this paper whether methods applicable to single metal lines are better suited for modelling purposes. Rotation and strong magnetic fields are shown to affect seriously the 'differential' field measure; polarity errors are not uncommon. The 'integral' ('centre-of-gravity') method - equivalent to Babcock's original method - on the other hand is insensitive to rotation but subject to the effects of saturation. Elucidating the weighting of the integrated magnetic field we point out the importance of Zeeman intensification. Equivalent widths vary with field strength and direction depending on the Zeeman pattern, resulting in a field measure that differs from line to line. Together with the effects of saturation, this variable weighting function leads to a 'natural' scatter about the mean relation between the Zeeman shift and the intensity weighted mean displacement of the sigmacomponents. Despite the uncertainty introduced by this scatter it is still possible to define a 'correct' mean effective field. Finally we outline an improved approach to the modelling of stellar magnetic field configurations.
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