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Astron. Astrophys. 325, 360-366

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The de-censoring of the faint stars in Tycho photometry*

J.L. Halbwachs1, T. Di Méo1, M. Grenon2, V. Großmann3, E. Høg4, and A. Wicenec3

1Observatoire Astronomique de Strasbourg, Equipe "Populations Stellaires et Evolution galactique", 11, rue de l'Université,
F-67000 Strasbourg, France
2Observatoire de Genève, 51, chemin des Maillettes, CH-1290 Sauverny, Switzerland
3Institut für Astronomie und Astrophysik der Universität Tübingen, Waldhäuser Str. 64, D-72076 Tübingen, Germany
4Copenhagen University Observatory, Juliane Maries Vej 30, DK-2100 Copenhagen OE, Denmark

Received 10 January 1997 / Accepted 10 March 1997


The Tycho catalogue provides astrometric and photometric data for more than 1 million stars. The derivation of the mean magnitudes of stars fainter than about 8 mag required a dedicated treatment, in order to take into account the observations that were too faint for providing a measurable signal. This treatment, called "de-censoring", is based on a statistical model permitting to substitute mean values to the missing data. Faint photometric standard stars are used to demonstrate that the de-censoring produces reliable magnitudes and uncertainties.

Key words: methods: data analysis - methods: statistical - techniques: photometric - catalogs

*Based on observations made with the ESA Hipparcos satellite

Send offprint requests to: J.L. Halbwachs

© European Southern Observatory (ESO) 1997