The authors report orbital solutions for 40 binaries in the Carney and Latham survey of proper-motion stars. They confirm the earlier orbital solutions for HD 85091, BD +13°3683, and HD 195987, and revise that for BD -3°2525. The authors have increased the number of orbital solutions for metal-poor binaries ([m/H] < -1.2) from five to 19, six of which have double lines. For the metal-poor binaries, they find that all the short-period orbits are circular, with a transition to eccentric orbits at a period somewhere between 13 and 18 days. Presumably, the close binaries with short periods were formed with eccentric orbits which were subsequently circularized by tidal mechanisms. There is good promise that this phenomenon can be used to determine the age of the halo population of binaries, and thus the age of our galaxy. The observations indicate that among high-proper-motion stars, metal-poor binaries may be more common than metal-rich ones.
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Latham et al. (1988) studied this question.