UBVRI photopolarimetry of the long-period eclipsing AM Herculis binary V1309 Ori

Abstract

We report simultaneous UBVRI photopolarimetric observations of the long-period (7.98 h) AM Her binary V1309 Ori. The length and shape of the eclipse ingress and egress vary from night to night. We suggest that this is a result of the variation in the brightness of the accretion stream. By comparing the phases of circular polarization zero-crossovers with previous observations, we confirm that V1309 Ori is well synchronized, and find an upper limit of 0. 002 per cent for the difference between the spin and orbital periods. We model the polarimetry data using a model consisting of two cyclotron emission regions at almost diametrically opposite locations, and centred at colatitude β= 35° and 145° on the surface of the white dwarf. We also present archive X-ray observations which show that the negatively polarized accretion region is X-ray bright.