Tycho-2 Catalogue

 WCSTools Catalogs
The Tycho-2 Catalogue is an astrometric reference catalogue containing positions and proper motions as well as two-colour photometric data for the 2,539,913 of the brightest stars in the sky. Components of double stars with separations down to 0.8 arcsec are included. The catalog is 99% complete to V~11.0 and 90% complete to v~11.5.

The Tycho-2 positions and magnitudes are based on precisely the same observations as the Tycho-1 Catalogue (ESA SP-1200, 1997) 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.

Proper motions precise to about 2.5 mas/yr are given as derived from a comparison with the Astrographic Catalogue (AC) and 143 other ground-based astrometric catalogues, all reduced to the Hipparcos celestial coordinate system. For only about 100,000 stars, no proper motion could be derived. For stars brighter than Vt=9, the astrometric error is 7 milliarcseconds; for all stars, the error is 60 milliarcseconds. The mean satellite observation epoch is 1991.5.

Photometric accuracy for stars brighter than Vt=9 is 0.013 magnitude; for all stars it is 0.10 magnitude.

To enable rapid access of specific stars in the catalog, WCSTools software numbers each star using its Guide Star region number (0001-9537) and a five-digit star number within each region, separated by a decimal point. sty2 lists Tycho-2 stars by number or sky region. imty2 lists the Tycho-2 stars within an IRAF or FITS image using the world coordinate system defined in its header.

A Perl program for extracting data from the catalog is available from http://archive.eso.org/ASTROM/.

Tycho-2 File Formats

WCSTools software uses the files catalog.dat and index.dat.

Reference

Hog, E.; Fabricius, C.; Makarov, V. V.; Urban, S.; Corbin, T.; Wycoff, G.; Bastian, U.; Schwekendiek, P.; Wicenec, A. (2000) The Tycho-2 catalogue of the 2.5 million brightest stars Astronomy & Astrophysics, v.355, p.L27-L30.
ADS Abstract

Get the Catalog

The following FTP sites make the Tycho-2 catalog available as 19 gzipped files. After retrieveing them and the index.dat file, combine the gzipped files into catalog.dat. The resulting files will differ from the files on the CDROM in that they will end lines with only a linefeed, while the CDROM version for which WCSTools software was written, terminates lines with a carriage return and a linefeed. Add back carriage returns to the files using the unix2dos -ascii command.

Put the catalog.dat and index.dat files in a subdirectory data/ to the directory pointed to by the TY2_PATH environment parameter or the ty2cd variable in libwcs/ty2read.c.

[sty2] [imty2]