6. Conclusions

The multiple star catalogue is an attempt to unite most of available observational data on multiple stars. Its study leads to the following conclusions:

• MSC is complete to the distance of 10 pc from the Sun. Only 1/3 of multiple systems within 22.5 pc are actually catalogued.
• The vast majority of multiple systems are hierarchical.
• Comparison of the orbital periods of wide and close sub-systems at adjacent hierarchical levels shows that there is no preferred period ratio.
• The distribution of short periods has a depression in the range from 5 d to 30 y which is likely to be due to observational selection.
• The idea that component masses are independently selected from the Salpeter mass function seems to correspond to the observed mass ratio distribution.
• Only a fraction of available hierarchical levels is filled.
• Orbital angular momentum vectors of wide and close sub-systems show a weak tendency of alignment.

MSC can serve as a database for the preparation of future observing programs concerning multiple stars. Some possible programs can be mentioned:

• Multiplicity search among nearby stars.
• Component census and the definition of the sample of complete multiple systems. Such a sample is needed for statistical study of the degree of multiplicity and level, period and mass ratio distributions. Complete component census is possible for nearby stars by combining precise radial velocity measurements over long time span with high resolution and high dynamic range imaging.
• Orbit coplanarity studies by means of interferometric resolution of close sub-systems. It will be also interesting to compare the properties of systems with coplanar and non-coplanar orbits.
• Relation of multiple stars to other stellar groups such as clusters and associations, multiplicity - age relation.

Acknowledgements

A large part of this project was accomplished while the author was a visitor at the Observatoire de Grenoble. The discussions with C. Perrier, A. Chalabaev, T.Forveille and other colleagues are gratefully acknowledged, as well as their help. F. Fekel kindly read the manuscript and suggested some improvements. The comments of the referee J. Dommanget were useful for improving the article. The extensive use of the SIMBAD database operated by the Strasbourg University was critical for the catalogue compilation. This work was supported by the International Science Foundation (grant MPB 000) and by the France-Russia international collaboration program (PICS).