T Tauri stars (TTSs) show enhanced ultraviolet (UV) continuum and line emission with respect to main sequence stars of similar spectral types (Imhoff & Appenzeller 1989; Gomez de Castro, 1998). There is mounting evidence of this excess being produced by the release of gravitational energy from infalling material (Bertout et al 1988, Simon et al 1990, Gomez de Castro & Fernandez, 1996). In particular, Bertout et al (dy1988) have shown that the UV excess of the TTSs can be produced at the boundary layer between the accretion disk and the star assuming accretion rates of ∼ 3 (l0-7 - pp10-9) M⨀yr-1. However, it is now evident that some properties of the TTSs cannot be explained with this simple boundary-layer model since some TTSs exhibit periodic photometric variability which is most likely produced by the presence of hot spots on the stellar surface.