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The dynamical importance of binary systems in young massive star clusters

Published online by Cambridge University Press:  31 March 2017

Richard de Grijs ,
Chengyuan Li  and
Aaron M. Geller
Richard de Grijs
Affiliation:
Kavli Institute for Astronomy & Astrophysics and Department of Astronomy, Peking University, Beijing, China email: grijs@pku.edu.cn
Chengyuan Li
Affiliation:
Kavli Institute for Astronomy & Astrophysics and Department of Astronomy, Peking University, Beijing, China email: grijs@pku.edu.cn Purple Mountain Observatory, Chinese Academy of Sciences, Nanjing, China
Aaron M. Geller
Affiliation:
Center for Interdisciplinary Exploration and Research in Astrophysics (CIERA) and Department of Physics and Astronomy, Northwestern University, Evanston, IL, USA Department of Astronomy and Astrophysics, University of Chicago, Chicago, IL, USA
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Abstract

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Characterization of the binary fractions in star clusters is of fundamental importance for many fields in astrophysics. Observations indicate that the majority of stars are found in binary systems, while most stars with masses greater than 0.5M⊙ are formed in star clusters. In addition, since binaries are on average more massive than single stars, in resolved star clusters these systems are thought to be good tracers of (dynamical) mass segregation. Over time, dynamical evolution through two-body relaxation will cause the most massive objects to migrate to the cluster center, while the relatively lower-mass objects remain in or migrate to orbits at greater radii. This process will globally dominate a cluster’s stellar distribution. However, close encounters involving binary systems may disrupt ‘soft’ binaries. This process will occur more frequently in a cluster’s central, dense region than in its periphery, which may mask the effects of mass segregation. Using high resolution Hubble Space Telescope observations, combined with sophisticated N-body simulations, we investigate the radial distributions of the main-sequence binary fractions in massive young Large Magellanic Cloud star clusters. We show that binary disruption may play an important role on very short timescales, depending on the environmental conditions in the cluster cores. This may lead to radial binary fractions that initially decline in the cluster centers, which is contrary to the effects expected from dynamical mass segregation.

Keywords

stellar dynamicsmethods: statisticalbinaries: generalMagellanic Cloudsgalaxies: star clusters
Type
Contributed Papers
Information
Proceedings of the International Astronomical Union , Volume 12 , Symposium S316: Formation, evolution, and survival of massive star clusters , August 2015 , pp. 222 - 227
Copyright
Copyright © International Astronomical Union 2017 

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