How do binaries affect the derived dynamical mass of a star cluster?

M. B. N. Kouwenhoven; R. de Grijs

doi:10.1007/s10509-009-0123-6

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arXiv · 0801.3941

How do binaries affect the derived dynamical mass of a star cluster?

M. B. N. Kouwenhoven·R. de Grijs

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Abstract

The dynamical mass of a star cluster can be derived from the virial theorem, using the measured half-mass radius and line-of-sight velocity dispersion of the cluster. However, this dynamical mass may be a significant overestimation of the cluster mass if the contribution of the binary orbital motion is not taken into account. In these proceedings we describe the mass overestimation as a function of cluster properties and binary population properties, and briefly touch the issue of selection effects. We find that for clusters with a measured velocity dispersion of sigma > 10 km/s the presence of binaries does not affect the dynamical mass significantly. For clusters with sigma < 1 km/s (i.e., low-density clusters), the contribution of binaries to sigma is significant, and may result in a major dynamical mass overestimation. The presence of binaries may introduce a downward shift of Delta log(L/Mdyn) = 0.05-0.4 in the log(L/Mdyn) vs. age diagram.

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M. B. N. Kouwenhoven, R. de Grijs. 2008-01-25. How do binaries affect the derived dynamical mass of a star cluster?. https://doi.org/10.1007/s10509-009-0123-6

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