Westerlund 1: bound or unbound?

Abstract

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.

6 pages, 3 figs., to appear in the proceedings of the meeting "Young massive star clusters - Initial conditions and environments", Granada, Spain, 2007

References in corpus (8)

• Optimization of Starburst99 for Intermediate-Age and Old Stellar Populations
• Gas expulsion and the destruction of massive young clusters
• On the massive stellar population of the Super Star Cluster Westerlund 1
• The Star Cluster Population of M51: II. Age distribution and relations among the derived parameters
• Star Cluster Demographics. I. A General Framework and Application to the Antennae Galaxies
• Dynamical Masses of Young Star Clusters in NGC 4038/4039
• Star-formation in NGC 4038/4039 from broad- and narrow band photometry: Cluster Destruction?
• Medium resolution 2.3 micron spectroscopy of the massive Galactic open cluster Westerlund 1

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• A serendipitous survey for variability amongst the massive stellar population of Westerlund 1
• Is the massive young cluster Westerlund I bound?
• The growth of massive stars via stellar collisions in ensemble star clusters
• Clues to the star formation in NGC 346 across time and space
• The Chemical Signature of a Relic Star Cluster in the Sextans Dwarf Spheroidal Galaxy - Implications for Near-Field Cosmology
• A VLT/FLAMES survey for massive binaries in Westerlund 1. III. The WC9d binary W239 and implications for massive stellar evolution
• Stellar age spreads in clusters as imprints of cluster-parent clump densities
• Maser Observations of Westerlund 1 and Comprehensive Considerations on Maser Properties of Red Supergiants Associated with Massive Clusters
• SIEGE III: The formation of dense stellar clusters in sub-parsec resolution cosmological simulations with individual star feedback
• The mass function and dynamical mass of young star clusters: Why their initial crossing-time matters crucially
• The discovery of a molecular cavity in the Norma near arm associated to H.E.S.S gamma-ray source located in the direction of Westerlund 1
• Report of IAU Commission 30 on Radial Velocities (2009-2012)
• Structure and Dynamics of the Young Massive Star Cluster Westerlund 1