Calibration of radii and masses of open clusters with a simulation

TL;DR

This study uses N-body simulations to evaluate how projection effects and cluster age bias mass estimates of open clusters when using tidal radius methods, revealing significant overestimations especially for young clusters.

Contribution

It quantifies the bias in mass determination of open clusters due to projection effects and age, providing correction insights for observational methods.

Findings

Mass overestimation ranges from 10-50%, up to 3.5 times for young clusters.

Projection direction significantly influences mass estimates.

Mass segregation systematically reduces derived limiting radii.

Abstract

Context: A recent new approach to apply a simple dynamical mass estimate of tidally limited star clusters is based on the identification of the tidal radius in a King profile with the dynamical Jacobi radius. The application to an unbiased open cluster catalogue yields significantly higher cluster masses compared to the classical methods. Aims: We quantify the bias in the mass determination as function of projection direction and cluster age by analysing a simulated star cluster. Methods: We use direct $N$-body simulations of a star cluster including stellar evolution in an analytic Milky Way potential and apply a best fit to the projected number density of cluster stars. Results: We obtain significantly overestimated star cluster masses which depend strongly on the viewing direction. The overestimation is typically in the range of 10-50 percent and reaches a factor of 3.5 for young clusters. Mass segregation reduces the derived limiting radii systematically.