  Joint statistics of periods and mass ratios of close binaries and its
dependence on primary mass can be explained by assuming that seed binary
companions are formed by disc fragmentation at random intervals during
assemblage of stellar mass and migrate inwards as they accrete from the
circumbinary disk. A toy model based on simple prescriptions for the companion
growth and migration reproduces such aspects of close solar-mass binaries as
the distribution of binary periods P, the brown dwarf desert at short P, the
nearly uniform distribution of mass ratios, and a population of equal-mass
binaries (twins) that decreases linearly in frequency with logP. For massive
stars, the model predicts a large fraction of early mergers, a distribution of
logP with a negative slope, and a mass-ratio distribution that is also uniform
but with a substantially reduced twin fraction. By treating disc fragmentation
as a stochastic process, we also reproduce the observed properties of compact
triples. Success of our toy model suggests that most close binaries and compact
triples indeed formed by disc fragmentation followed by accretion-driven inward
migration.
