Is the massive young cluster Westerlund I bound?

Westerlund I is the richest young cluster currently known in the authors' Galaxy, making it one of the most massive clusters for which they can resolve the individual stars even in the crowded centre. They measure the radial velocity dispersion of Westerlund I to explore whether the cluster is either currently in virial equilibrium, in the process of collapse, or expanding and dispersing into the field. They obtained MIKE/Magellan high resolution optical spectra of 22 post main-sequence stars in Westerlund I for 2 epochs or 3 epochs with a maximum baseline of about one year. Radial velocities variations between these spectra are measured by means of cross-correlation. They calculate the velocity dispersion from the cross-correlation of five yellow hypergiants and one luminous blue variable, that show little radial velocity variations between epochs and have many spectral features in common. After taking into account the effect of small number statistics and undetected binaries, they estimate the velocity dispersion for the massive stars in Westerlund I to be ... (ProQuest: ... denotes formulae/symbols omitted.)