Biases in the determination of dynamical parameters of star clusters: today and in the Gaia era

Journal
Date Issued
2015
Author(s)
•
Baumgardt, H.
•
Zocchi, A.
•
Balbinot, E.
•
Gieles, M.
•
Hénault-Brunet, V.
•
Varri, A. L.
DOI
Description
We thank the anonymous referee for his/her helpful comments and suggestions. AS acknowledges the PRIN INAF 2011 ‘Multiple populations in globular clusters: their role in the Galaxy assembly’ (PI E. Carretta). We warmly thank Michele Bellazzini for useful discussions. MG thanks the Royal Society for financial support in the form of a University Research Fellowship (URF) and the European Research Council (ERC-StG-335936, CLUSTERS). We used Gaia Challenge data products available at http://astrowiki.ph.surrey.ac.uk/dokuwiki .
Abstract
The structural and dynamical properties of star clusters are generally derived by means of the comparison between steady-state analytic models and the available observables. With the aim of studying the biases of this approach, we fitted different analytic models to simulated observations obtained from a suite of direct N-body simulations of star clusters in different stages of their evolution and under different levels of tidal stress to derive mass, mass function and degree of anisotropy. We find that masses can be under/overestimated up to 50 per cent depending on the degree of relaxation reached by the cluster, the available range of observed masses and distances of radial velocity measures from the cluster centre and the strength of the tidal field. The mass function slope appears to be better constrainable and less sensitive to model inadequacies unless strongly dynamically evolved clusters and a non-optimal location of the measured luminosity function are considered. The degree and the characteristics of the anisotropy developed in the N-body simulations are not adequately reproduced by popular analytic models and can be detected only if accurate proper motions are available. We show how to reduce the uncertainties in the mass, mass function and anisotropy estimation and provide predictions for the improvements expected when Gaia proper motions will be available in the near future.
Volume
451
Issue
2
Start page
2185
Uri
Url
Issn Identifier
0035-8711
Ads BibCode
2015MNRAS.451.2185S
Rights
open.access
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