  The Galactic open cluster Westerlund 1 (Wd 1) represents the ideal local
template for extragalactic young massive star clusters, because it is currently
the only nearby young cluster which reaches a mass of around 10^5 Msun. The
proximity makes spatially resolved studies of its stellar population feasible,
and additionally permits direct comparison of its properties with measurements
of velocity dispersion and dynamical mass for spatially unresolved
extragalactic clusters.
  Recently, we published the dynamical mass estimate based on spectra of four
red supergiants. We have now identified six additional stars which allow a
determination of radial velocity from the wavelength covered in our VLT/ISAAC
near-infrared spectra (CO bandhead region near 2.29micron), improving
statistics significantly. Using a combination of stepping and scanning the slit
across the cluster centre, we covered an area which included the following
suitable spectral types: four red supergiants, five yellow hypergiants, and one
B-type emission line star.
  Our measured velocity dispersion is 9.2 km/s. Together with the cluster size
of 0.86 pc, derived from archival near-infrared SOFI-NTT images, this yields a
dynamical mass of 1.5x10^5 Msun. Comparing this to the mass derived via
photometry, there is no indication that the cluster is currently undergoing
dissolution.
