Effect of binarity in star cluster dynamical mass determination
  In this paper we explore the effects that the presence of a fraction of
binary stars has in the determination of a star cluster mass via the virial
theorem. To reach this aim in an accurate and consistent way, we run a set of
simulations using the direct summation, high precision, code NBODY7. By means
of this suite of simulations we are able to quantify the overestimate of
open-star-cluster-like models' dynamical masses when making a straight
application of the virial theorem using available position and radial velocity
measurements. The mass inflation caused by the binary 'heating' contribution to
the measured velocity dispersion depends, of course, on the initial binary
fraction, $f_{b0}$ and its following dynamical evolution. For an $f_{b}$
(evolved up to 1.5 Gyr) in the range $8\% - 42\%$ the overestimate of the mass
done using experimentally sounding estimates for the velocity dispersion can be
up to a factor 45. We provide a useful fitting formula to correct the dynamical
mass determination for the presence of binaries, and underline how neglecting
the role of binaries in stellar systems might lead to erroneous conclusions
about their total mass budget. If this trend remains valid for larger systems
like dwarf spheroidal galaxies, which are still far out of reach for high
precision dynamical simulations taking account their binaries, it would imply
an incorrect over-estimation of their dark matter content, as inferred by means
of available velocity dispersion measurements.
