The Hipparcos Photometry and Variability Annexes

A summary of the photometric data obtained by the Hipparcos and Tycho missions is presented. The photometric signals and their reduction to magnitudes are described, as well as the passbands and their evolution. The main mission photometry provided on average 110 observations for each of the 118 000 stars observed during the mission. The accuracies for this epoch photometry range from a few millimagnitudes for the brightest stars to a few hundreds of a magnitude for the fainter ones. The data coverage was very much a function of ecliptic latitude, with the most homogeneous coverage near the ecliptic poles, and the most observations close to ecliptic latitude 47 . The Hipparcos epoch photometry for all stars was investigated for variability and around 970 new periodic variables were discovered, as well as some 7000 unresolved variables (including micro variables, irregular variables, as well as variables for which a period could not be determined based on the Hipparcos data only). Median magnitudes as well as course variability indicators, derived from the epoch photometry, are included in the the main astrometric catalogue. All Hipparcos epoch photometry has been made available on the ASCII CD-ROM, disks 2 and 3. The Tycho epoch photometry was of lower accuracy, but provided useful colour index information. Only epoch photometry for a selection of the brighter stars in the Tycho catalogue has been preserved on the ASCII CD-ROM disk 4. More epoch photometry can be obtained through the CDS in Strasbourg. Mean magnitudes obtained from the Tycho photometry are, when available, included in the main Hipparcos astrometric catalogue.