A PRELIMINARY LIST OF STARS FROM TYCHO OBSERVATIONS

The final Tycho Catalogue will be a major source of astrometric standa rd stars when it will be published, in 1997. While the Tycho positions with their full accuracy will only be available at the end of the dat a reduction, it is already possible to derive a preliminary list of ab out one million stars from the Tycho Input Catalogue (TIC) which have a high probability of appearing in the final Tycho Catalogue. We expec t this list to be useful for programs needing a high density coverage of reference stars, with a rather homogeneous magnitude limit, such as photographic astrometry, preparation and reduction of ground-based or space-based surveys, etc. Users of the list will be able to work with the current positions (mostly derived from the Guide Star Catalog), a nd to plan a further iteration, with improved reductions, based on the final Tycho positions when they become available. The list is derived from the TIC Revision (TICR) which is based on the first year of Tych o observations. It consists of the TIC entries for which at least one star has been found in the TICR with a separation less than 6 arcsec f rom the TIC position. About 2 percent of the entries in the list will not appear in the final Tycho Catalogue, because they are artifacts fr om the data reduction. The list is available through the astronomical data centers.