Multiplicity of Solar-Type Stars

Abstract

AbstractA systematic search for binaries in a sample of 123 bright field stars of types F3-G2 IV or V is described. Combination of the results for 25 newly discovered spectroscopic binaries with those of 21 spectroscopic, 23 visual, and 25 common-proper-motion pairs previously known brings to 88 the total number of companions identified in the sample. The distribution of the 88 periods shows a single maximum; the median period is 14 years.The frequencies of singles: doubles: triples: quadruples are found to be 42: 46: 9: 2. Less than half of the stars are thus observed to be single. Estimates of the completeness of this search lead to a determination of the number of systems missed and to a determination of their secondary masses.Analysis of the secondary-mass distributions, observed and predicted from completeness estimates, indicates the existence of two types of binaries.For systems with periods less than about 100 years, the distribution of secondaries varies with the cube-root of the secondary mass. These systems must be the result of fission. Two-thirds of their primaries have companions of stellar mass. Extrapolation of the cube-root relation implies that the remaining one-third of the primaries have non-stellar secondaries, i.e., close companions whose masses are less than 0.07 solar masses.For systems with periods larger than roughly 100 years the distribution of secondaries follows that given by the van Rhijn function. They must be the result of condensations that contracted separately but are bound gravitationally. Roughly three-fourths of all primaries in the sample have such distant companions, all of which are likely to be themselves close fission-systems. Evidently single stars are rare among solar-type dwarfs.