Variable stars in the Tycho photometric observations - I. Detection

We present an original way to detect variable stars in the Tycho photometri c observations. A modified Kolmogorov-Smirnov statistical test has been con structed, based on a model of most of the satellite's parameters, leading t o the dispersion in the measurements. This allows us to build a treatment t aking into account truncated detections and censored measurements, and to s earch for variability in the faint part of the catalogue. The selection thr eshold of variable stars has been calibrated to minimize false alarm rate. Reliable results were thus obtained for stars as faint as 11 mag. One thous and and ninety-one suspected variable stars have been listed, 407 of which are already known in Hipparcos, GCVS or NSV, and 684 of which are suspected variable stars to be identified soon.