... Edwards

Present address: Australia Telescope National Facility, CSIRO, PO Box 76, Epping NSW 1710, Australia.

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... angle

The ellipticity angle ( $\chi=\frac{1}{2}\tan^{-1} V/(Q^2+U^2)^{1/2}$) complements the position angle to completely specify the orientation of a polarization vector in QUV space, independent of its length.

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... OPMs

Purely sinusoidal modulations are confined to elliptical paths by definition, but the presence of higher harmonics, neglected in our analysis, could in principle allow for any closed locus in $\vec{p}$ space. Nevertheless, the ellipticity of the fundamental is proof that the locus is not confined to a line.

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