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1 Introduction

The processing of the Hipparcos observations culminated in June 1997 with the official publication of the astrometric solutions of nearly 118000 stars included in the Hipparcos Catalogue (ESA 1997). The average astrometric precision for the bulk of the Catalogue is about 1 mas in each of the five astrometric parameters: position, parallax and the two components of the proper motion. However, due to time constraints, it was known at the time of publication that the solutions for about one thousand stars were not fully satisfactory and for 263 entries no solutions at all were found acceptable from the data.

The raw data have been archived by each of the two consortia and intermediate data have been published with the other Hipparcos products. Relieved from the pressure of the publication schedule we have revisited the solutions not considered as final in the Hipparcos Catalogue, taking advantage of updated information regarding their multiplicity status. The criteria used to identify the doubtful Hipparcos solutions are given below in Sect. 3, but by itself this flagging was not a sufficient condition to start a new processing.

First, new information not used in the mass processing had to be available, otherwise there were no chances to get something really different. Secondly, as a result of the organisation of the file storage in the FAST consortium, there were only about 20000 stars detected as non-single for which a new double star treatment was feasible. Thus all the stars re-examined for duplicity problems were in this set. The vast majority of the improved solutions belong to this category.

Unlike the results available in the Hipparcos Catalogue, the solutions presented in this paper do not follow from a cross-check between the two consortia and are entirely based on the software developed by teams of the FAST consortium and published under the sole scientific responsability of the authors.


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