Infrared Observations of AR Ursa Majoris: Modeling the Ellipsoidal Variations

We have obtained time-series infrared photometry for the highly magnetic cataclysmic variable AR UMa. Our J and K’ band observations occurred during a low state and they show a distinctive double-humped structure. Using detailed models for the expected ellipsoidal variations in the infrared due to the non-spherical secondary star, we find that the most likely value for the system inclination is 70. We also model low state V band photometry and find that its observed double-humped structure is not caused by ellipsoidal variations, as they have been ascribed to, but are due to beamed cyclotron radiation. We use this result to estimate the magnetic field strength of the active southern accretion region (B∼< 190 MG) and its magnetic longitude (ψS∼330 ). Subject headings: cataclysmic variables − stars: binaries: close − stars: magnetic − stars: low mass