Issue |
A&A
Volume 466, Number 1, April IV 2007
|
|
---|---|---|
Page(s) | 151 - 155 | |
Section | Galactic structure, stellar clusters, and populations | |
DOI | https://doi.org/10.1051/0004-6361:20066717 | |
Published online | 05 February 2007 |
Medium resolution 2.3
m spectroscopy of the massive
Galactic open cluster Westerlund 1*
European Southern Observatory (ESO), Karl-Schwarzschild-Str. 2, 85748 Garching, Germany e-mail: smengel@eso.org
Received:
8
November
2006
Accepted:
5
January
2007
The Galactic open cluster Westerlund 1 was found only a few
years ago to be much more massive than previously thought, with evidence
suggesting its mass to be in excess of ~10@,
in the range spanned by young extragalactic star clusters.
Unlike those clusters, its proximity makes spatially resolved studies of its
stellar population feasible. It is therefore an ideal template for a young,
massive star cluster, permitting direct comparison of its properties with
measurements of velocity dispersion and dynamical mass for spatially unresolved
extragalactic clusters.
To this end, we used the long slit near-infrared spectrograph
VLT/ISAAC to observe the CO bandhead region near 2.29 μm,
scanning the slit across the cluster centre during the integration.
Spatially collapsing the spectra along the slit results in a
single co-added spectrum of the cluster, comparable to what one would obtain in
the extragalactic cluster context.
This spectrum was analysed in the same way as the spectra of almost point-like
extragalactic clusters, using red superiant cluster members as velocity templates.
We detected four red supergiants that are included in the integrated
spectrum, and our measured velocity dispersion is 5.8 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
. While this
value is not to be considered the final word, there is at least so far no sign
of rapid expansion or collapse.
Key words: open clusters and associations: individual: Westerlund 1 / galaxies: star clusters / supergiants
© ESO, 2007
Current usage metrics show cumulative count of Article Views (full-text article views including HTML views, PDF and ePub downloads, according to the available data) and Abstracts Views on Vision4Press platform.
Data correspond to usage on the plateform after 2015. The current usage metrics is available 48-96 hours after online publication and is updated daily on week days.
Initial download of the metrics may take a while.