List of Figures

• A polarization modulator.
• ISIS polarimeter schematic, with representative beam cross-sections and polarization ellipses.
• ISIS polarization modulator and slit area.
• Theoretical performance of superachromat halfwave. Actual as-made properties of ISIS superachromat can be measured in situ.
• Planning aid to set slit vertical at mid-exposure; courtesy Robert Laing. The curve labels are declination values.
• Scattered light causing false sky polarization. See text.
• Linear polarization as a vector quantity. In each case, the complete circle denotes the rms error, the circular arcs are loci of constant degree of polarization. See text.
• Actual performance of a halfwave plate similar to that of ISIS.
• Wavelength-dependence of the apparent polarization angle. This is a direct consequence of specifying super-achromatism of the retardation; observations need to be corrected for this effect.
• Optical elimination of sky polarization.
• Dekker frame with Dekkers used during commissioning. Actual suite of Dekkers will be different from this. See text.
• Tests on `unpolarized' star during commissioning (courtesy Dave Axon, Jim Hough). Lower panel is with calibration Polaroid in the beam; drop-off of degree of polarization at low pixel numbers is due to Polaroid failure.
• Extract from Tinbergen 1979: zero-polarization stars.
• Extract from Hsu and Breger 1982: standard stars for degree and angle of polarization, in 5 broad bands. Use with Bailey and Hough 1982, Whittet et al 1992.
• Extract from Dolan and Tapia 1986: polarization variations in `standard stars'.
• Extract from Bastien et al. 1988: polarization variations in `standard stars'.
• Extract from Turnshek et al. 1990: HST polarization standards.
• Extract from Turnshek et al. 1990: HST high-polarization extended objects.
• Extract from Bailey and Hough 1982: standard stars for degree and angle of polarization, in 9 broad bands (U to K). Use with Whittet et al 1992, Hsu and Breger 1982.
• Bibliography of polarization standards up to 1985.