THE DE-CENSORING OF THE FAINT STARS IN TYCHO PHOTOMETRY

The Tycho catalogue provides astrometric and pho- tometric data for more than 1 million stars. The derivation of the mean magnitudes of stars fainter than about 8 mag required a dedicated treatment, in order to take into account the obser- vations that were too faint for providing a measurable signal. This treatment, called \de-censoring", is based on a statistical model permitting to substitute mean values to the missing data. Faintphotometricstandardstarsareusedtodemonstratethatthe de-censoring produces reliable magnitudes and uncertainties.