Eccentric Orbits in Samples of Circularized Binary Systems: The Fingerprint of a Third Star

Three short-period binaries, whose orbits should have been circularized long ago, have been found with small eccentricities. The eccentricities are attributed to a third star, which can modulate the binary eccentricity with a relatively long timescale. It is shown that strong spectroscopic indications for the existence of a third star have already been observed in all three systems. The frequency of close binaries with another distant companion is discussed; some evidence is presented that about half of the spectroscopic binaries are in fact triple systems.