2018MNRAS.481.3953A

We have selected archival observational data for several O and B trapezia in the Milky Way. For each of the main components of the trapezia, we obtained transverse velocities from the historical separation data. With this information, and with the stellar masses of the main components, we studied the dynamical evolution of ensembles of multiple systems mimicking each one of the trapezia. For this purpose we conducted numerical N-body integrations using the best available values for the masses, the observed positions and transverse velocities, randomly generated radial velocities, and random line-of-sight (z) positions for all components. Random perturbations were assigned to the observed quantities, compatible with the observational errors. A large fraction of the simulated systems (between 70 and 90 per cent) turned out to be unbound. The properties of the evolving systems are studied at different values of the evolution time. We find that the dynamical lifetimes of both the bound and unbound seem to be quite short, less than 10 000 yr for the unbound systems and 10 000 to 20 000 yr for the bound systems. The end result of the simulations is usually a binary with semi-axes of a few hundred au, sometimes a triple of hierarchical or non-hierarchical type. Non-hierarchical triples formed during the integrations (which are dynamically unstable) were found to have much longer lifetimes, of 250 000 to 500 000 yr. The frequency distributions of the major semi-axes and eccentricities of the resulting binaries are discussed and compared with observational properties of binary systems from the literature.