THE CLASSICAL T-TAURI STAR SZ-68 - DOPPLER IMAGING AND EVIDENCE FOR MAGNETOSPHERIC ACCRETION

We have Doppler imaged the surface of the classical T Tauri star St 68 , both under the assumption of solid-body rotation as well as allowing for differential rotation. Assuming solid-body rotation, we find evid ence for a large, cool, polar spot similar to those found on previousl y imaged naked T Tauri stars. Allowing for substantial levels of antis olar differential rotation in the image reconstruction causes the bulk of the polar spot to disappear, although several small spots remain a t latitude +60 degrees. Checks between the various lines marginally fa vor the solid-body rotation case. We examine the potential influence o f accretion hot spots on the line profiles in St 68, concluding that w e are unable to resolve these structures in our Doppler image of the s tar. We also examine the H alpha and Na I line profiles in this star a nd compare their variations to the stellar surface image. We conclude that the H alpha line is formed primarily in an accretion flow, and we find strong evidence that this accretion flow is modulated by the ste llar rotation. These results are most easily interpreted within the fr amework of magnetospheric accretion models for classical T Tauri stars . The phasing of accretion as traced by redshifted absorption in the H alpha line profile compared with the stellar surface image strongly s uggests a dipole magnetic held inclined by approximately 15 degrees wi th the rotation axis in this star.