Detection and measurement of double stars with the HIPPARCOS satellite - NDAC reductions

The Hipparcos satellite has a predefined observing program given by an Input Catalogue with 118000 entries. This includes about 10000 members of known double or multiple systems (with separations above 0.1 arcsec and magnitude differences below 4-5), which will be observably non-single and thus need a more complex reduction procedure. Also, a similar number of objects showing deviations from a single-star observation model will be included in these double star reductions, and a few thousand hitherto unknown doubles may thus be discovered. This paper describes the methods used by the Northern Data Analysis Consortium (NDAC) for detecting supected non-singles and for determining the photometric and astrometric parameters for the non-single objects