A survey of third components in spectroscopic and eclipsing systems

Summary Multiplicities recorded in catalogues as well as in the current literature are considered. The basis of the statistical treatment is about one half of the material collected in theSeventh Catalogue of spectroscopic binaries by A. Batten and his collaborators, subjected also to a magnitude limit atV=6.8, altogether 310 systems. It is hoped that this sample of brighter stars represents close and also wider systems with a reasonable degree of completeness. Incidence of higher multiple systems, in particular of ab-c-type triple stars, turns out rather high: the ratio of double to multiple systems is about 2:1, in terms of the directly observed data. Allowing for some more obvious observational bias, this ratio approaches 1:1. The number of individual components in multiple systems is almost certainly superior to that of double star components. An investigation in progress, concerning multiplicities in the specific classes of W UMa-systems and cataclysmic variables, is briefly described.