Modelling the photopolarimetric variability of AA Tau

We present Monte Carlo scattered light models of a warped disc that reproduce the observed photopolarimetric variability of the classical T Tauri star, AA Tauri. For a system inclination of 75 degrees and using an analytic description for a warped inner disc, we find that the shape and amplitude of the photopolarimetric variability are reproduced with a warp that occults the star, located at 0.07 au, amplitude 0.016 au, extending over radial and azimuthal ranges 0.0084 au and 145 degrees. We also show a time sequence of high spatial resolution scattered light images, showing a dark shadow cast by the warp sweeping round the disc. Using a modified smooth particle hydrodynamics code, we find that a stellar dipole magnetic field of strength 5.2 kG, inclined at 30 degrees to the stellar rotation axis can reproduce the required disc warping to explain the photopolarimetric variability of AA Tau.