The Hipparcos measurement system is not optimum for the observation and detection of all categories of double and multiple stars. If the components of such systems are sufficiently well separated, and sufficiently bright, each component may be observed separately, and may be included in the main catalogue according to its astrophysical or astrometric interest. However, for closer systems, or systems with fainter components, the instantaneous field of view of the Hipparcos observations may be centred on only one of the components, or on the geometric centre, or on the photocentre, depending on the precise geometric and photometric configuration of the system.
Annex 1 gives information and data for all known individual components of around fourteen thousand double and multiple systems for which at least one component is identified in the main Hipparcos Input Catalogue, i.e. when at least one component of the system is observed by the Hipparcos satellite. Because of their astronomical interest, all known components of double or multiple systems involved in the Hipparcos observations have been collected together in Annex 1, even though they may be completely negligible, in the context of the Hipparcos observations, because of their faint magnitude or distance from the primary component.
Annex 1 was constructed from a subset of a preliminary version of the Catalogue of Components of Double and Multiple Stars (CCDM, Dommanget at al., in preparation). A complete description of the information contained in the CCDM will be given in its first edition. This subset was supplemented by 452 stars (candidates for observation with Hipparcos) discovered as double systems by M. Rousseau when measuring ESO Survey Schmidt plates within the preparatory programme of ground-based measurements.
The INCA data base (the source of the main catalogue), and the preliminary version of CCDM (the source of Annex 1), have necessarily evolved separately during the course of the Input Catalogue preparation. However, systematic comparisons were made regularly between them in order to improve their agreement. In some cases, in the construction of Annex 1, data from the INCA data base have been preferred (for example, in the case of magnitudes or some proper motions), while in other cases, data from the CCDM were retained (for example, positions of components of the same system when they originate from the same source catalogue). This choice has been necessary in order to preserve the internal consistency of the (relative) data on the various components of a system, whilst at the same time preserving the `absolute' positional information required for the Hipparcos observations. As a result, there are discrepancies between the details of such systems in the main catalogue and in Annex 1.
The systems are ordered by increasing CCDM numbers (constructed from equatorial coordinates at equinox and epoch J2000.0). For a same right ascension, the systems are ordered from the North to the South Pole. Each system is distinguished from the next one by a blank line. The CCDM and HIC numbers provide the link between the main catalogue and this annex.