BiPoS1 -- a computer programme for the dynamical processing of the initial binary star population

Abstract

The first version of the Binary Population Synthesizer (BiPoS1) is made publicly available. It allows to efficiently calculate binary distribution functions after the dynamical processing of a realistic population of binary stars during the first few Myr in the hosting embedded star cluster. Instead of time-consuming N-body simulations, BiPoS1 uses the stellar dynamical operator Ω ρ ecl dyn (log 10 (E b ), t), which determines the fraction of surviving binaries depending on the binding energy of the binaries, E b . The Ω-operator depends on the initial star cluster density, ρ ecl , as well as the time, t, until the residual gas of the star cluster is expelled. BiPoS1 has also a galactic-field mode, in order to synthesize the stellar population of a whole galaxy. At the time of gas expulsion, the dynamical processing of the binary population is assumed to effiently end due to the subsequent expansion of the star cluster. While BiPoS1 has been used previously unpublished, here we demonstrate its use in the modelling of the binary populations in the Orion Nebula Cluster, in OB associations and as an input for simulations of globular clusters.