The origin of the visual and infrared pulsations in the intermediate polar FO Aqr (H2215–086)

Simultaneous visual and infrared polarimetry of the intermediate polar FO Aqr (H2215–086) shows that its visual and infrared pulsations, seen at the rotation period of the white dwarf, are not circularly polarized. This is despite the fact that the infrared pulsations come from optically thin material: if cyclotron emission is important, it must be efficiently depolarized without the pulsations being hidden. We describe how this may come about, and discuss what further measurements will best establish whether cyclotron emission is important. The visual pulsations come from opaque material, and most likely arise from reprocessing at the surface of the white dwarf, but the possibility that cyclotron emission is important in the visual too cannot be definitely excluded.