LIMITS ON THE DIFFERENTIAL ROTATION OF T-TAURI STARS

The hypothesis that strong differential rotation coupled with the pref erential appearance of higher latitude hot spots on classical T Tauri stars (CTTS) and low latitude cool spots on naked T Tauri stars (NTTS) can account for the apparent difference in the rotation periods of th e two groups of stars is tested. It is shown that the required level o f differential rotation produces measurable changes in the profile sha pes of the photospheric absorption lines. High spectral resolution obs ervations of 1 NTTS (HDE 283572 - vsini approximate to 110 km s(-1)) a nd 2 CTTS (SU Aur - vsini approximate to 66 km s(-1); RY Tau - vsini a pproximate to 50 km s(-1)) are analyzed for the presence of differenti al rotation. It is shown that these stars are consistent with solid-bo dy rotation and rule out the strong differential rotation required to explain the rotation period difference between CTTS and NTTS. This fur ther supports the hypothesis that CTTS do in fact rotate slower than N TTS due to the interaction of stellar magnetic fields with the accreti on disks which surround CTTS. In addition, a more accurate measure of vsini approximate to 80 km s(-1) for HDE 283572 is given.