Linear polarimetry of AP stars. 1. A simple canonical model
Abstract
The present knowledge of the magnetism of Ap stars derives essentially from the analysis of the longitudinal Zeeman effect. The transverse Zeeman effect is more difficult to observe but it contains important information on the angular parameters which describe the `oblique rotator'. This effect can be conveniently studied via broadband polarization measurements: among the previously published results, the Kemp & Wolstencroft (1974) contribution has revealed to be particularly interesting, especially after a theoretical interpretation has been given for the time variation of linear polarization (Landi Degl'Innocenti et al. 1981). This example remained however an isolated one and we have decided to tackle again the same type of investigation with the help of the Pic du Midi 2-meter telescope.
Although the general theory of the phenomenon is now quite clear, we have considered useful to analyze in some detail an inversion procedure allowing to determine the parameters of the magnetic field from the observed polarization. To this aim we have developed a canonical model which provides simple analytical solutions to the inversion problem. These solutions are shown to give a close approximation to the broadband polarization obtained through more rigorous calculations. The present work is limited to the classical schemes of the dipolar and quadrupolar magnetic structure, although in principle it could be extended to more complex configurations.- Publication:
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Astronomy and Astrophysics
- Pub Date:
- May 1993
- Bibcode:
- 1993A&A...272..285L
- Keywords:
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- polarization;
- stars: magnetic fields;
- stars: peculiar