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Astron. Astrophys. 359, 1195-1200 (2000)

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5. The Hipparcos Catalogue

As a result of the Hipparcos mission two astrometric catalogues were produced, the Hipparcos Catalogue, containing about 120000 stars, and the Tycho Catalogue with more than one million stars. The stellar coordinates were obtained from observations conducted by the satellite in the period 1989.85-1993.21; the epoch of Hipparcos catalogue is J1991.25. The stellar Hipparcos coordinates represent the International Celestial Reference System (ICRS) within [FORMULA] for the three axes; the residual rotations of the Hipparcos frame with respect to the ICRF are at level of [FORMULA] also for the three axes (ESA 1997). The IAU adopted Hipparcos Stellar Catalogue as the realization of the ICRS in optical wavelengths.

The basic astrometric data in Hipparcos Catalogue includes positions, proper motions and trigonometric parallaxes of 118218 stars. For visual magnitudes up to 9 the median astrometric precision for single stars at the epoch of the catalogue is 0.77 mas for the right ascensions and 0.64 mas for the declinations, 0.88 and 0.74 mas/yr for the proper motions in right ascension and declination respectively. The density of the catalogue is of three stars per square degree with a limiting magnitude of 12.4.

It is to be noted that Hipparcos Catalogue (1997) has not been tied to the FK5 system, but only to the ICRS. Considering that this latter is coincident with the FK5 within its uncertainties (Arias et al. 1995), Hipparcos frame can be regarded as representing the J2000 (FK5) system but without its regional errors (Mignard & Froeschlé 2000).

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© European Southern Observatory (ESO) 2000

Online publication: July 13, 2000