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Binaries and the Dynamical Mass of Star Clusters

Published online by Cambridge University Press:  01 September 2007

M. B. N. Kouwenhoven
Affiliation:
Department of Physics and Astronomy, University of Sheffield, Hicks Building, Hounsfield Road, Sheffield S3 7RH, United Kingdom email: [email protected]
R. de Grijs
Affiliation:
National Astronomical Observatories, Chinese Academy of Sciences, 20A Datun Road, Chaoyang District, Beijing 100012, P.R. China email: [email protected]
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Abstract

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The total mass of a distant star cluster is often derived from the virial theorem, using line-of-sight velocity dispersion measurements and half-light radii, under the implicit assumption that all stars are single (although it is known that most stars form part of binary systems). The components of binary stars exhibit orbital motion, which increases the measured velocity dispersion, resulting in a dynamical mass overestimation. In these proceedings we quantify the effect of neglecting the binary population on the derivation of the dynamical mass of a star cluster. We find that the presence of binaries plays an important role for clusters with total mass Mcl ≤ 105 M; the dynamical mass can be significantly overestimated (by a factor of two or more). For the more massive clusters, with Mcl ≥ 105 M, binaries do not affect the dynamical mass estimation significantly, provided that the cluster is significantly compact (half-mass radius ≤qslant 5 pc).

Type
Contributed Papers
Copyright
Copyright © International Astronomical Union 2008

References

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