RESULTS ON TYCHO PHOTOMETRY

The final Tycho database will contain astrometric and photometric data for about 1 million stars. Here we discuss the results of the Tycho p hotometric calibration for about 80% of the data acquired by the star mapper of the Hipparcos satellite and estimate the photometric precisi on in the final Tycho photometric data base. For a non-variable star o f 7th (10th) magnitude with approximate to 100 observations a precisio n of better than 10 mmag (40 mmag) can be expected in the Tycho star c atalogue. The precision on (B - V)(T) depends only slightly on the col our and is exptected to be better than 20 mmag (60 mmag) for the same number of observations. These results will be representative of the fi nal Tycho photometric quality.