MAGNETICALLY MODULATED ACCRETION IN T-TAURI STARS

We examine how accretion on to T Tauri stars may be modulated by a time-dependent 'magnetic gate' where the inner edge of the accretion disc is disrupted by a varying stellar held. We show that magnetic field variations on time-scales much less than 10(5) yr can modulate the accretion flow, thus providing a possible mechanism both for the marked photometric variability of T Tauri stars and for the possible conversion of T Tauri stars between classical and weak line status. We thus suggest that archival data relating to the spectrophotometric variability of T Tauri stars may provide an indirect record of magnetic activity cycles in low-mass pre-main-sequence stars.