Field 1: Hipparcos Input Catalogue (HIC) running number

The star entries are ordered by increasing HIC number. This numbering basically follows the order of the object's right ascension (equinox J2000.0), independent of declination. The catalogue epoch is J2000.0, although stars with unknown proper motion are referred to their original epoch of measurement. There is one entry in the main catalogue corresponding to each satellite target, irrespective of the possible multiplicity of the star. If the star is a component of a known double or multiple system, fields 2-3 provide further information.

Entries which have been suppressed from the observing programme after launch, and therefore result in HIC numbers no longer contained within the Input Catalogue, are listed in Table A1 (page ).

[]The Hipparcos Input Catalogue running number was created in 1988, for the first preliminary version distributed to ESA, to ESOC (ESA's European Space Operations Centre), and to the Data Reduction Consortia. This first version was used for the development of the software for operating the satellite, and for reducing the Hipparcos data. One consequence of the Input Catalogue's development is that increasing HIC number does not always correspond precisely to the order of increasing right ascension (field 4) for two reasons:

• from the start of the Input Catalogue work, the star entries have been ordered and numbered for epoch J1990.0, corresponding to the mean epoch adopted for Hipparcos operational considerations, rather than for epoch J2000.0, the epoch adopted for the Input Catalogue publication;
• after the start of the satellite operations, and as a result of verifications made on the early observations, some stars were deleted from the programme, and some corrections to the catalogue entries were made. Where this resulted in a change in position of more than several arcsec, a new HIC running number was allocated to the star in order to provide a clear update at the operational level, and to avoid any possible confusion within the data reductions. These 24 recently-assigned numbers, unrelated to the right ascension of the affected entry, lie between 120001 and 120313.

As ordered by right ascension, 33 stars are out of sequence by 10 to 20 places, and 70 by 5 to 9 places. Stars for which the displacement would have been larger than 20 entries have been allocated a number larger than 120000. The 137 `missing' HIC numbers, resulting from these reallocations or from suppression of the original target after launch, are given in Table A1 (page ). The 24 `additional' HIC numbers, ordered by increasing running number with their right ascension, and by right ascension, are listed in Table A2/1 (page ) and TableA2/2 (page ) respectively.