Spectroscopic binaries with circular orbits.

Abstract

Because of observational errors, a spectroscopic binary with a truly circular orbit will be found to have an elliptical orbit of small, but nonzero, eccentricity. This effect is analyzed and shown to lead to spurious eccentricities comparable with those assigned to a great many binaries. We then argue, following Luyten, that such elliptical orbits should be rejected in favor of circular orbits. In order to eliminate these spurious eccentricities, an extensive program of orbit recomputation has been carried out for single-lined systems hitherto assigned orbits of small eccentricity (e<0.1). Adopting the 5% level of significance for accepting an elliptical orbit, we find 103 systems whose elliptical orbits should be rejected. As a result of these calculations, most single-lined systems with periods less than 5 days now have circular orbits. We find also that many long-period binaries with late-type giant components now have circular orbits.