Discrete dynamical models of ω Centauri

Abstract

We present a new framework for modelling discrete kinematic data. Current techniques typically involve binning. Our approach works directly with the discrete data and uses maximumlikelihood methods to assess the probability of the data set given model predictions.We avoid making hard cuts on the data sets by allowing for a contaminating population in our models. We apply our models to discrete proper motion and line-of-sight velocity data of Galactic globular cluster ω Centauri and find a mildly radial velocity anisotropy β = 0.10 ± 0.02, an inclination angle i = 50° ± 1°, a V-band mass-to-light ratio γ = 2.71 ± 0.05 M⊙/L⊙and a distance d = 4.59 ± 0.08 kpc. All parameters are in agreement with previous studies, demonstrating the feasibility of our methods. We find that the models return lower distances and higher mass-to-light ratios than expected when we include proper motion stars with high errors or for which there is some blending. We believe this not a fault of our models but is instead due to underestimates or missing systematic uncertainties in the provided errors. © 2013 The Authors Published by Oxford University Press on behalf of the Royal Astronomical Society.