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NIR Spectroscopy of the Most Massive Open Cluster in the Galaxy: Westerlund 1

Published online by Cambridge University Press:  01 September 2007

S. Mengel  and
L. E. Tacconi-Garman
S. Mengel
Affiliation:
ESO, Karl-Schwarzschild-Str. 2, 85748 Garching, Germany email: smengel@eso.org, ltacconi@eso.org
L. E. Tacconi-Garman
Affiliation:
ESO, Karl-Schwarzschild-Str. 2, 85748 Garching, Germany email: smengel@eso.org, ltacconi@eso.org
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Abstract

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Using ISAAC/VLT, we have obtained individual spectra of all NIR-bright stars in the central 2′ × 2′ of the cluster Westerlund 1 (Wd 1) with a resolution of R ≈ 9000 at a central wavelength of 2.30 μm. This allowed us to determine radial velocities of ten post-main-sequence stars, and from these values a velocity dispersion. Assuming virial equilibrium, the dispersion of σ = 8.4 km/s leads to a total dynamical cluster mass of 1.25 × 105M⊙, comparable to the photometric mass of the cluster. There is no extra-virial motion which would have to be interpreted as a signature of cluster expansion or dissolution.

Keywords

open clusters and associations: individual: (Westerlund 1)galaxies: star clusterssupergiants

References

Goodwin, S. P & Bastian, N. 2006, MNRAS 373, 752CrossRefGoogle Scholar
Mengel, S. & Tacconi-Garman, L. E. 2007, A&A 466, 151Google Scholar