Orbits of 22 spectroscopic binaries in the open cluster M67

Orbits are presented for 22 spectroscopic binaries in the field of the old open cluster M67. The binary frequency and the distribution of orbital eccentricity are discussed. The detected binary frequency is in the range 9-15 percent, somewhat lower than that found among solar-mass stars in the field. A transition from circular to eccentric orbits among main-sequence binaries at a period between 10.3 and 11.0 days is found, longer than similar transition periods found in younger binary populations. An increase of transition period with cluster age is consistent with the interpretation that the shorter-period orbits have been tidally circularized. A circular orbit at a period of 43 days is found for the cluster giant S1040, consistent with the theoretical expectation that more effective tidal circularization occurs with increasing stellar radius and deepening convective zones.