Published online by Cambridge University Press: 12 April 2016
A radial velocity survey of the components of visual multiple stars has been done since 1994 with the correlation radial velocity spectrometer. About 50 spectroscopic sub-systems have been discovered, and a summary of the 30 published orbits is given. Difficulties of measuring the radial velocities of multiple stars are discussed and illustrated by 2 examples. New discoveries will lead to a better understanding of the formation of multiple stellar systems. Close and wide sub-systems can not be considered as a result of independent random combination, but are related by common origin. Almost all close binaries with periods less than 6 days possibly have more distant components which assisted in the formation of close pairs by taking away their angular momentum. On the other hand, among the distant visual tertiary companions the frequency of sub-systems with periods under 100 days is about 3 times higher than for field G dwarfs.