The Tycho-2 Catalogue

Frequently asked questions
"Where are the Hipparcos and Tycho Catalogues available, with the CD-ROMs ? "

They can no longer be ordered from ESA since the printed volumes have been sold out, but they are available in many scientific libraries. Moreover, the volumes 1-11 are available on the web: Hipparcos and Tycho Catalogues. The data on the CD-ROMs are available at the Strasbourg Data Centre from where all astronomical catalogues may be obtained.

"Where can I find an overview of astronomical catalogues ? "

An overview of all kinds of astronomical catalogues has been placed at the homepage of the US Naval Observatory by Zacharias et al. (2004): "Catalog Information and Recommendations" .

"Why is a bright star like HIP 11767 (Polaris) missing in Tycho-2 ?"

There is indeed a problem with HIP 11767, but it is not missing! HIP 11767 is TYC 4628-237-1.
Tycho-2 gives, as always, the observed position on the sky and also the two-colour photometry. What is missing is the proper motion. About 4% of the Tycho-2 stars were not found is the ground based catalogues which we used for determining the proper motions. For these stars we are therefore unable to provide the epoch 2000 mean position and proper motion. What we do give, is the observed position, which was observed at an epoch around 1991.5. You should check the "mean position flag" in column 14. This flag distinguishes between three kinds of Tycho-2 stars:

'  ' =
normal mean position and proper motion.
'P' =
Close double stars resolved in Tycho-2, but the epoch 2000 mean position, proper motion, etc., refer to the photo-centre of the two Tycho-2 entries, where the BT magnitudes were used in weighting the positions.
'X'=
stars, like Polaris, with no epoch 2000 mean position and no proper motion.
"Could you provide the photometric transmission curves ?"

Yes, here

"Where do I find formulae for the rigorous transformation of positions to an arbitrary epoch ?"

In a good textbook on astrometry, or on the Hipparcos homepage in Volume 1 of the Hipparcos and Tycho Catalogues (ESA 1997) available at the link given at the top of the page; see Section 1.5.

"Where do I find Tycho epoch photometry ? I have a sample of variable stars and want to see what Tycho gives. "

Tycho-1 epoch photometry is provided in the Annexes A and B for 481553 Tycho Catalogue objects (see Section 2.6 in Volume 1 of the Hipparcos and Tycho Catalogues (ESA 1997) available at the link given at the top of the page. Annex A is provided on disc 4 of the ESA CD-ROMs. Please ask Strasbourg directly to get the Annex B.
Tycho-2 epoch photometry has not been published, and will not be.

Last updated 14 November 2008 / Tycho-2@astro.ku.dk