A prescription and fast code for the long-term evolution of star clusters - II. Unbalanced and core evolution

Gieles, Mark, Alexander, Paul E. R., Lamers, Henny J. G. L. M. and Baumgardt, Holger (2013) A prescription and fast code for the long-term evolution of star clusters - II. Unbalanced and core evolution. Monthly Notices of the Royal Astronomical Society, 437 1: 916-929. doi:10.1093/mnras/stt1980

Author Gieles, Mark
Alexander, Paul E. R.
Lamers, Henny J. G. L. M.
Baumgardt, Holger
Title A prescription and fast code for the long-term evolution of star clusters - II. Unbalanced and core evolution
Journal name Monthly Notices of the Royal Astronomical Society   Check publisher's open access policy
ISSN 0035-8711
Publication date 2013-01-01
Year available 2013
Sub-type Article (original research)
DOI 10.1093/mnras/stt1980
Open Access Status DOI
Volume 437
Issue 1
Start page 916
End page 929
Total pages 14
Place of publication Oxford, United Kingdom
Publisher Oxford University Press
Language eng
Abstract We introduce version two of the fast star cluster evolution code Evolve Me A Cluster of StarS (EMACSS). The first version (Alexander and Gieles) assumed that cluster evolution is balanced for the majority of the life cycle, meaning that the rate of energy generation in the core of the cluster equals the diffusion rate of energy by two-body relaxation, which makes the code suitable for modelling clusters in weak tidal fields. In this new version, we extend the model to include an unbalanced phase of evolution to describe the pre-collapse evolution and the accompanying escape rate such that clusters in strong tidal fields can also be modelled. We also add a prescription for the evolution of the core radius and density and a related cluster concentration parameter. The model simultaneously solves a series of first-order ordinary differential equations for the rate of change of the core radius, half-mass radius and the number of member stars N. About two thousand integration steps in time are required to solve for the entire evolution of a star cluster and this number is approximately independent of N.We compare the model to the variation of these parameters following from a series of direct N-body calculations of single-mass clusters and find good agreement in the evolution of all parameters. Relevant time-scales, such as the total lifetimes and core collapse times, are reproduced with an accuracy of about 10 per cent for clusters with various initial half-mass radii (relative to their Jacobi radii) and a range of different initial N up to N = 65 536. The current version of EMACSS contains the basic physics that allows us to evolve several cluster properties for single-mass clusters in a simple and fast way. We intend to extend this framework to include more realistic initial conditions, such as a stellar mass spectrum and mass-loss from stars. The EMACSS code can be used in star cluster population studies and in models that consider the co-evolution of (globular) star clusters and large-scale structures.
Keyword Galaxies: Star clusters: General
Galaxy: Kinematics and dynamics
Globular clusters: General
Methods: numerical
Open clusters and associations: general
Stars: Kinematics and dynamics
Q-Index Code C1
Q-Index Status Confirmed Code
Institutional Status UQ

Document type: Journal Article
Sub-type: Article (original research)
Collections: School of Mathematics and Physics
Official 2014 Collection
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Citation counts: TR Web of Science Citation Count  Cited 9 times in Thomson Reuters Web of Science Article | Citations
Scopus Citation Count Cited 1 times in Scopus Article | Citations
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