We present the first multi-epoch radial velocity study of embedded young massive stars using near–infrared spectra obtained with ISAAC mounted at the ESO Very Large Telescope , with the aim to detect massive binaries .
Our 16 targets are located in high–mass star–forming regions and many of them are associated to known ultracompact H II regions , whose young age ensures that dynamic evolution of the clusters did not influence the intrinsic binarity rate .
We identify two stars with about 90 km/s velocity differences between two epochs proving the presence of close massive binaries .
The fact that 2 out of the 16 observed stars are binary systems suggest that at least 20 % of the young massive stars are formed in close multiple systems , but may also be consistent with most if not all young massive stars being binaries .
In addition , we show that the radial velocity dispersion of the full sample is about 35 km/s , significantly larger than our estimated uncertainty ( 25 km/s ) .
This finding is consistent with similar measurements of the young massive cluster 30 Dor which might have a high intrinsic binary rate .
Furthermore , we argue that virial cluster masses derived from the radial velocity dispersion of young massive stars may intrinsically overestimate the cluster mass due to the presence of binaries .