Classical T Tauri Stars (CTTSs) show enhanced continuum (from UV to IR) and
line emission with respect to main sequence stars of similar spectral types.
It is commonly believed that this excess is due to mass accretion from
circumstellar disks. However the details of this process are not well
understood. For many years it was assumed that the material from the
viscous disk accretes steadily onto the star through the boundary layer
between the disk and the star . This
boundary layer was thought to be the responsible of the UV excess.
The detection of hot spots on the stellar surface of some
CTTS has made grow the suspicion that the infall could be chanelled by strong
dipolar fields on the stellar surface.
In fact, there are mounting evidences of the UV excess being produced by the
release of gravitational energy from infalling material as it
shocks with the stellar surface. This process is best studied in UV.
The analysis of the IUE Archive Data on T Tauri Stars (TTSs) show that 30 (out of a total of 126) have good quality spectra in the entire UV range covered by IUE. Most of these stars have been observed with ROSAT and Einstein satellites. We are studying a possible relation between UV data and X-rays fluxes.