Modelling the photopolarimetric variability of AA Tau

Abstract

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° 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°. 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° to the stellar rotation axis can reproduce the required disc warping to explain the photopolarimetric variability of AA Tau.