Gemini/GMOS detection of stellar velocity variations in the ionising cluster of 30 Dor

We have analysed spectra obtained with the Gemini Multi Object Spectrograph (GMOS) for more than 50 stars in the ionising cluster of 30 Doradus during a seven epochs observing campaign at Gemini South. We derive a binary candidate rate of about 50%, which is however consistent with an intrinsic 100% binary rate among massive stars. After decontaminating the sample from the stars that show binary orbital motions, we were able to calculate the “true” cluster velocity dispersion and found it to be about 8 km s^-1. This value implies a virial mass of about 4.5 × 10⁵ M_⊙ which is consistent with previous photometric mass determinations therefore suggesting that NGC 2070 is a firm candidate for a future globular cluster.