The impact of massive stars and black holes on the fate of open star
  clusters and their tidal streams
  Context: To investigate how the content of massive OB stars affects the
long-term evolution of young open clusters and their tidal streams, and how
such an effect influences the constraint of initial conditions by looking at
the present-day observations.
  Aims: OB stars are typically in binaries, have a strong wind mass loss during
the first few Myr, and many become black holes. These affect the dynamical
evolution of an open star cluster and impact its dissolution in a given
Galactic potential. We investigate the correlation between the mass of OB stars
and the observational properties of open clusters. Hyades-like star clusters
are well represented in the Solar neighborhood and thus allow comparisons with
observational data.
  Methods: We perform a large number of star-by-star numerical $N$-body
simulations of Hyades-like star clusters by using the high-performance $N$-body
code \textsc{petar} combined with \textsc{galpy}. We also developed the tool to
transfer the simulation data to mock observations of Gaia.
  Results: We find that OB stars and black holes have a major effect on star
cluster evolution. Star clusters with the same initial conditions, but a
different initial content of OB stars, follow very different evolutionary
paths. Thus, the initial total mass and radius of an observed star cluster
cannot be unambiguously determined unless the initial content of OB stars is
known. We show that the stellar counts in the corresponding tidal tails, that
can be identified in the Gaia data, help to resolve this issues. We thus
emphasise the importance of exploring not only star-clusters, but also their
corresponding tidal tails. These findings are relevant for studies of the
formation of massive stars.
