5 Conclusions

In spite of the relative low spectral resolution, our data already provide important new results about the dynamical state of the 30 Dor cluster. First, the velocity dispersion is much too large to be due random motions of the stars in the gravitational potential of the cluster. Instead, the observed dispersion seems to be entirely dominated by binary orbital motions. Thus, the first important results is that higher spectral resolution alone is not sufficient to probe the dynamics of the cluster; it is also crucial to have observations with good time resolution in order to find (and exclude) binaries. Second, there is no strong evidence for dynamical mass segregation in the sense of massive stars moving with lower random velocities. If present, the effect is masked by binaries, so again, it is crucial to obtain data for several epochs. Finally, the virial dynamical mass of the cluster is comparable within factors of a few with the photometric mass. Therefore, using a reasonable number of non-binary stars it should be possible to place useful constrains on the IMF slope below 1 $M_\odot$.

The strong conclusion of this investigation, therefore, is that it would be very worthwhile to obtain time resolved spectroscopy of a sample of 100-200 stars in the cluster. The FLAMES integral field spectrograph on the VLT appears ideally suited for such study.