Spectroscopy and polarimetry of the AM Herculis system RX J1313.32−3259

Abstract

We present polarimetric and spectroscopic observations of the ROSAT source RX J1313.32−3259, recently identified as a polar. Circular polarization is modulated over the orbital period with an amplitude of ∼10 per cent. A brief reversal in circular polarization is detected at phase ∼0.0, when the main accretion region is seen face on to the observer. We deduce that the main cyclotron emission is absorbed by the accretion shock and/or stream at this phase, allowing a second accretion shock, located at the opposite ends of the field lines that feed the main pole, to be seen. Linear polarization is also detected with possible linear pulses at orbital phases where the accretion region is expected to be on the limb of the white dwarf. The general morphology of the photopolarimetry arises as a result of a combination of the absorption of cyclotron radiation by the accretion shock/stream and projection/cyclotron beaming effects of a main cyclotron emission region as the white dwarf rotates. The main cyclotron emission region remains on the visible hemisphere of the white dwarf throughout the orbit. Doppler maps of the emission lines show emission at or near the expected location of the secondary star and an extended arc-like feature coincident with the ballistic and possibly the magnetically confined accretion stream.