MAGNETIC ACCRETION AND PHOTOPOLARIMETRIC VARIABILITY IN T-TAURI STARS

We investigate the photopolarimetric variability of a magnetic accreti on disk model for pre-main-sequence T Tauri stars. In these dynamical models, material from a magnetically truncated Keplerian disk accretes along magnetic field lines onto the stellar surface at high latitudes , producing ''hot spots'' on the stellar photosphere. These spots have been proposed as the origin of the UV excesses in T Tauri stars. As t he star rotates, the observed UV excess varies, as will the polarizati on arising from the intrinsically polarized spot the radiation of whic h is also scattered in the circumstellar disk. We calculate the photop olarimetric variability for a simple magnetic accretion model in which the hot spots are two diametrically opposed, circular regions with te mperatures much larger than the surrounding photosphere. Our Monte Car lo calculations show that the predicted amplitudes of the photopolarim etric variability are consistent with those observed in T Tauri stars. This model predicts correlations between the brightness and polarizat ion that can be tested with synoptic observations. The model also pred icts quasi-periodic variations if the hot spots remain relatively fixe d on the stellar surface on timescales comparable to the rotation peri od.