Variability of classical T Tauri stars - Its relation to the accretion process

We present the analysis of a UBV(RI)(c) photometric monitoring program carried out from July 1988 to August 1992 on a sample of 13 classical T Tauri stars and 2 suspected classical T Tauri stars. We detected optical irregular variability with an amplitude larger than 0.1 mag in the V band in 8 stars. For 5 of them most of the variability can be attributed to hot spots, for one, to cool spots and for two of them, there is no clear mechanism; nevertheless, other phenomena must explain the short term (hours - days) and long term (years) variations superimposed. For some objects an anomalous behaviour at the shorter wavelengths (U band) is detected. From the comparison between the amplitude of the optical variability due to hot spots and the equivalent width of the H-alpha emission a correlation between them is suggested. Assuming that the H-alpha emission is related to the accretion process, this correlation supports the idea that we are observing the hot spots where the material from the accretion disks falls onto the star.