8 Conclusions

  By providing the users with the intermediate astrometric data in the form of the actually observed abscissa residuals, a range of uses of the Hipparcos data has become possible that allows proper determination of statistical quantities, as well as the combination of Hipparcos data with other information, providing general determinations with improved reliability of quantities like cluster proper motions and parallaxes, as well as for luminosity calibrations.

Acknowledgements

The main reason that we have availability of the intermediate astrometric data was an initiative by C.A. Murray around 1993, when he explained that merging of the astrometric data could only be done reliably when using these abscissae data. C.A. Murray and F. Arenou developed and implemented the algorithms for the merging of the data, and F. Arenou provided some samples and further explanations. Discussions with L. Lindegren about some of the ideas presented here are also gratefully acknowledged. Discussions with U. Bastian and the implementation of the methods presented here to the Magellanic Clouds measurements were very beneficial. L.V. Morisson read the manuscript and indicated various possible small improvements. A number of mistakes were pointed out by Anthony Brown. Finally, the implementation in the distance determination of the Pleiades and the involvement of Cristina S. Hansen Ruiz in that project, also greatly contributed to the present paper. The referee provided constructive suggestions and comments which were much appreciated.