How do binaries affect the derived dynamical mass of a star cluster?
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.
Cite
@article{arxiv.0801.3941,
title = {How do binaries affect the derived dynamical mass of a star cluster?},
author = {M. B. N. Kouwenhoven and R. de Grijs},
journal= {arXiv preprint arXiv:0801.3941},
year = {2009}
}
Comments
6 pages, 5 figures, to appear in ``Young Massive Star Clusters - Initial Conditions and Environments'', 2008, Astrophysics & Space Science, eds. E. Perez, R. de Grijs, R. M. Gonzalez Delgado