Infrared and optical polarimetry of AM Herculis

Circular polarization observations of AM Herculis have been obtained at wavelengths from 0.55 micron (V) to 2.2 micron (K) using a simultaneous three-channel polarimeter. Polarizations of up to 20 per cent were observed at 2.2 micron, as high as those observed at any other wavelength. The form of the polarization curve showed substantial wavelength dependence with the 2.2 micron polarization being limited to a feature lasting for around 30 per cent of the cycle. The observations are discussed in terms of cyclotron models.