Magnetic Accretion and Photopolarimetric Variability in Classical T   Tauri Stars
  We employ a Monte Carlo radiation transfer code to investigate the multi- wavelength photopolarimetric variability arising from a spotted T Tauri star surrounded by a dusty circumstellar disk. Our aim is to assess the ability of the magnetic accretion model to explain the observed photopolarimetric variability of classical T Tauri stars, and to identify potentially useful observational diagnostics of T Tauri star/disk/spot parameters. We model a range of spot sizes, spot latitudes, inner disk truncation radii, and system inclination angles, as well as multiple disk and spot geometries. We find that the amplitude, morphology, and wavelength dependence of the photopolarimetric variability predicted by our models are generally consistent with existing observations; a flared disk geometry is required to reproduce the largest observed polarization levels and variations. Our models can further explain stochastic polarimetric variability if unsteady accretion is invoked, in which case irregular -- but correlated -- photometric variability is predicted, in agreement with observations.   Potentially useful observational diagnostics of system parameters of interest are discussed. We also investigate the reliability of modeling spot parameters via analytic fits to multi-band photometric variations. 
Keivan G. Stassun and Kenneth Wood