Statistical properties of spectroscopic binary stars

Abstract

As part of a study of the mass-ratio distribution of spectroscopic binary stars, the statistical properties of the systems in the Eighth Catalogue of the Orbital Elements of Spectroscopic Binary Stars, compiled by Batten et al. (1989), are investigated. Histograms are presented of the distributions of various parameters of the systems in the Catalogue as a whole, and compared to those of the previous edition. Histograms of binaries of various spectral types are presented. It is noticed that the early-type binaries in the Catalogue have on average higher radial-velocity am- plitudes, shorter periods, and smaller semi-major axes than late-type binaries. Late- type binaries have relatively more eccentric orbits. Whether the differences noticed between the early- and late-type binaries have any significance with respect to the population of binary stars in the Galaxy is not clear, because it is very hard to assess the extent to which the Catalogue is a statistically representative and complete sample. The distribution of semi-major axes a1 sin i varies considerably among different sub-samples. The mass-ratio distribution of single-lined spectroscopic binaries is, for all (sub-)samples, characterized by a decrease in the number of systems according to a power law as q --> 1, for q = Msec/Mprim > 0.25. The mass-ratio distribution of double-lined spectroscopic binaries (sbii) is, for all (sub-)samples but one, characterized by an increase in numbers according to a power law, as q --> 1. The exception to this general behaviour is the sample of sbii systems with magnitudes m < 5 m , which has its maximum at q = 0:65. The distributions are presented `as they are', without corrections for selection effects.