Evolution of the binary population in young dense star clusters
  Context: Field stars are not always single stars, but can often be found in
bound double systems. Since binary frequencies in the birth places of stars,
young embedded clusters, are sometimes even higher than on average the question
arises of how binary stars form in young dense star clusters and how their
properties evolve to those observed in the field population.
  Aims: We assess, the influence of stellar dynamical interactions on the
primordial binary population in young dense cluster environments.
  Methods: We perform numerical N-body simulations of the Orion Nebula Cluster
like star cluster models including primordial binary populations using the
simulation code nbody6++.
  Results: We find two remarkable results that have yet not been reported: The
first is that the evolution of the binary frequency in young dense star
clusters is independent predictably of its initial value. The time evolution of
the normalized number of binary systems has a fundamental shape. The second
main result is that the mass of the primary star is of vital importance to the
evolution of the binary. The more massive a primary star, the lower the
probability that the binary is destroyed by gravitational interactions. This
results in a higher binary frequency for stars more massive than $2\Msun$
compared to the binary frequency of lower mass stars. The observed increase in
the binary frequency with primary mass is therefore most likely not due to
differences in the formation process but can be entirely explained as a
dynamical effect.
  Conclusions: Our results allow us to draw conclusions about the past and the
future number of binary systems in young dense star clusters and demonstrate
that the present field stellar population has been influenced significantly by
its natal environments.
