Westerlund 1: bound or unbound?

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 with a mass of similar to 10(5) M(aS (TM)). Its 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 2.29 mu m), significantly improving statistics. Using a combination of stepping and scanning the slit across the cluster center, 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(-1). 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) M(aS (TM)). Comparing this to the mass derived via photometry, there is no indication that the cluster is currently undergoing dissolution.