The effect of binaries on the dynamical mass determination of star clusters

摘要: The total mass of distant star clusters is often derived from the virial theorem, using line-of-sight velocity dispersion measurements and half-light radii. Although most stars form in binary systems, this mostly ignored when interpreting observations. components exhibit orbital motion, which may increase measured dispersion, therefore result a dynamical overestimation. In paper we quantify effect neglecting population on derivation cluster. We simulate numerically, study dependence properties population. find that presence binaries plays crucial role for very sparse with stellar density comparable to field (~0.1 stars pc -3 ), as fully dominated by motion. For such clusters, overestimate true up an order magnitude. dense ($\ga$10 7  stars pc do not affect estimation significantly. intermediate (0.1–10 can be overestimated 10–100%, depending