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Astron. Astrophys. 355, L27-L30 (2000)

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Letter to the Editor

The Tycho-2 catalogue of the 2.5 million brightest stars  *

E. Hog 1, C. Fabricius 1, V.V. Makarov 1, S. Urban 2, T. Corbin 2, G. Wycoff 2, U. Bastian 3, P. Schwekendiek 3 and A. Wicenec 4

1 Copenhagen University Observatory, Juliane Maries Vej 30, 2100 Copenhagen O, Denmark
2 United States Naval Observatory, 3450 Massachusetts Ave N.W., Washington DC 20392-5420, USA
3 Astronomisches Rechen-Institut, Mönchhofstrasse 12-14, 69120 Heidelberg, Germany
4 European Southern Observatory, Karl-Schwarzschild-Strasse 2, 85748 Garching, Germany

Received 3 January 2000 / Accepted 21 January 2000


The Tycho-2 Catalogue presented here is an astrometric reference catalogue containing positions and proper motions as well as two-colour photometric data for the 2.5 million brightest stars in the sky. The Tycho-2 positions and magnitudes are based on precisely the same observations as the original Tycho Catalogue (hereafter Tycho-1) collected by the star mapper of the ESA Hipparcos satellite, but Tycho-2 is much bigger and slightly more precise, owing to a more advanced reduction technique. Components of double stars with separations down to 0.8 arcsec are included. Proper motions precise to about 2.5 mas/yr are given as derived from a comparison with the Astrographic Catalogue and 143 other ground-based astrometric catalogues, all reduced to the Hipparcos celestial coordinate system. Tycho-2 supersedes in most applications Tycho-1, as well as the ACT and TRC catalogues based on Tycho-1.

Key words: astrometry – stars: fundamental parameters – catalogs

* Based on observations made with the ESA Hipparcos astrometry satellite. The catalogue is distributed on CD-ROM and through the astronomical data centres, and further information is given on the website http://www.astro.ku.dk/~erik/Tycho-2 .

© European Southern Observatory (ESO) 2000

Online publication: March 9, 2000