The statistical properties of stars and their dependence on metallicity
  We report the statistical properties of stars and brown dwarfs obtained from
four radiation hydrodynamical simulations of star cluster formation, the
metallicities of which span a range from 1/100 to 3 times the solar value.
Unlike previous similar investigations of the effects of metallicity on stellar
properties, these new calculations treat dust and gas temperatures separately
and include a thermochemical model of the diffuse interstellar medium. The more
advanced treatment of the interstellar medium gives rise to very different gas
and dust temperature distributions in the four calculations, with lower
metallicities generally resulting in higher temperatures and a delay in the
onset of star formation. Despite this, once star formation begins, all four
calculations produce stars at similar rates and many of the statistical
properties of their stellar populations are difficult to distinguish from each
other and from those of observed stellar systems. We do find, however, that the
greater cooling rates at high gas densities due to the lower opacities at low
metallicities increase the fragmentation on small spatial scales (disc,
filament, and core fragmentation). This produces an anti-correlation between
the close binary fraction of low-mass stars and metallicity similar to that
which is observed, and an increase in the fraction of protostellar mergers at
low metallicities. There are also indications that at lower metallicity close
binaries may have lower mass ratios and the abundance of brown dwarfs to stars
may increase slightly. However, these latter two effects are quite weak and
need to be confirmed with larger samples.
