The initial period function of late-type binary stars and its variation
  The variation of the period distribution function of late-type binaries is
studied. It is shown that the Taurus--Auriga pre-main sequence population and
the main sequence G dwarf sample do not stem from the same parent period
distribution with better than 95 per cent confidence probability. The Lupus,
Upper Scorpius A and Taurus--Auriga populations are shown to be compatible with
being drawn from the same initial period function (IPF), which is inconsistent
with the main sequence data. Two possible IPF forms are used to find parent
distributions to various permutations of the available data which include Upper
Scorpius B (UScB), Chameleon and Orion Nebula Cluster pre-main sequence
samples. All the pre-main sequence samples studied here are consistent with the
hypothesis that there exists a universal IPF which is modified through
binary-star disruption if it forms in an embedded star cluster leading to a
general decline of the observed period function with increasing period. The
pre-main sequence data admit a log-normal IPF similar to that arrived at by
Duquennoy & Mayor (1991) for main sequence stars, provided the binary fraction
among pre-main sequence stars is significantly higher. But, for consistency
with proto-stellar data, the possibly universal IPF ought to be flat in log-P
or log-semi-major axis and must be similar to the K1 IPF form derived through
inverse dynamical population synthesis, which has been shown to lead to the
main sequence period function if most stars form in typical embedded clusters.
