7 Catalogue content

  The Tycho Reference Catalogue contains 990182 stars. For each of them, the following data is provided:

• Tycho identifier.
• Right ascension and declination at epoch J2000.0 with respect to the ICRS reference system. The equatorial coordinates given in the catalogue were derived from the right ascensions and declinations at the respective mean epochs (cf. Sect. 5.1) by applying the TRC proper motions. From the comparison with Hipparcos, the accuracy of the TRC positions at epoch J2000.0 is estimated as 25-45 mas, depending on magnitude. This is close to the Tycho positional accuracy at epoch J1991.25, as expected.
• Standard errors of right ascension and declination for the respective mean epochs.
• Proper motion components in right ascension and declination, along with their estimated external errors. The catalogue provides final proper motions; the error estimates given in the catalogue represent a combination of the internal standard errors and the residual systematic error estimates derived from comparing TRC with the Hipparcos and Tycho Catalogues (cf. Sect. 6).
• Tycho photometry and the respective standard errors.
• Additional data related to the proper motion derivation, e.g. the mean epoch of right ascensions and declinations, the number of positions used to derive the proper motion, and proper motion quality flag.
• Flags indicating known or suspected variability/duplicity.
• Cross-identification with Hipparcos and other catalogues.

A detailed description of the catalogue can be found in the documentation accompanying the machine-readable version of the Tycho Reference Catalogue, made available at the Centre de Données Astronomiques de Strasbourg (CDS).