The Formation and Evolution of Binaries in Globular Clusters

AbstractThe number density of stars in the cores of globular clusters is high enough for close encounters between stars to be frequent. These encounters may lead to the formation of binaries. Those binaries which do not easily form via the evolution of primordial main-sequence star binaries, and are therefore rare in the galactic disk, can be common in globular clusters. Examples of such binaries are the low-mass X-ray binaries. Such binaries may evolve into radiopulsars.

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X-ray sources in Galactic globular clusters and old open clusters

Proceedings of the International Astronomical Union ◽

10.1017/s1743921319007981 ◽

2019 ◽

Vol 14 (S351) ◽

pp. 367-376

Author(s):

Maureen van den Berg

Keyword(s):

Globular Clusters ◽

Cataclysmic Variables ◽

Star Clusters ◽

Open Clusters ◽

Encounter Rate ◽

X Ray ◽

Low Mass ◽

New Perspective ◽

X Ray Binaries ◽

Cluster Age

AbstractThe features and make up of the population of X-ray sources in Galactic star clusters reflect the properties of the underlying stellar environment. Cluster age, mass, stellar encounter rate, binary frequency, metallicity, and maybe other properties as well, determine to what extent we can expect a contribution to the cluster X-ray emission from low-mass X-ray binaries, millisecond pulsars, cataclysmic variables, and magnetically active binaries. Sensitive X-ray observations withXMM-Newton and certainlyChandra have yielded new insights into the nature of individual sources and the effects of dynamical encounters. They have also provided a new perspective on the collective X-ray properties of clusters, in which the X-ray emissivities of globular clusters and old open clusters can be compared to each other and to those of other environments. I will review our current understanding of cluster X-ray sources, focusing on star clusters older than about 1 Gyr, illustrated with recent results.

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THE X-RAY LUMINOSITY FUNCTION OF LOW MASS X-RAY BINARIES IN EARLY-TYPE GALAXIES, THEIR METAL-RICH, AND METAL-POOR GLOBULAR CLUSTERS

The Astrophysical Journal ◽

10.3847/0004-637x/818/1/33 ◽

2016 ◽

Vol 818 (1) ◽

pp. 33 ◽

Cited By ~ 14

Author(s):

Mark B. Peacock ◽

Stephen E. Zepf

Keyword(s):

Globular Clusters ◽

Luminosity Function ◽

Early Type ◽

X Ray ◽

Low Mass ◽

X Ray Binaries

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The Globular Cluster Population of X-ray Binaries

Symposium - International Astronomical Union ◽

10.1017/s0074180900160711 ◽

1987 ◽

Vol 125 ◽

pp. 187-197 ◽

Cited By ~ 5

Author(s):

Frank Verbunt ◽

Piet Hut

Keyword(s):

Globular Cluster ◽

Globular Clusters ◽

Mass Function ◽

Initial Mass Function ◽

Encounter Rate ◽

Formation Mechanisms ◽

Main Sequence Stars ◽

X Ray ◽

Low Mass ◽

X Ray Binaries

We discuss formation mechanisms for low-mass X-ray binaries in globular clusters. We apply the most efficient mechanism, tidal capture in close two-body encounters between neutron and main-sequence stars, to the clusters of our galaxy. The observed number of X-ray sources in these can be explained if the birth velocities of neutron stars are higher than estimated from velocity measurements of radiopulsars, or if the initial mass function steepens at high masses. We perform a statistical test on the distribution of X-ray sources with respect to the number of close encounters in globular clusters, and find satisfactory agreement between the tidal capture theory and observation, apart from the presence of low-mass X-ray binaries in four clusters with a very low encounter rate: Ter 1, Ter 2, Gr 1 and NGC 6712.EXOSAT observations indicate that some dim globular cluster sources may be less luminous than hitherto assumed, and support the view that the brighter dim sources may be soft X-ray transients in quiescence.

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Observational Evidence for the Origin of X-ray Sources in Globular Clusters

Proceedings of the International Astronomical Union ◽

10.1017/s1743921308015822 ◽

2007 ◽

Vol 3 (S246) ◽

pp. 301-310 ◽

Cited By ~ 7

Author(s):

Frank Verbunt ◽

Dave Pooley ◽

Cees Bassa

Keyword(s):

Statistical Method ◽

Globular Clusters ◽

Cataclysmic Variables ◽

Observational Evidence ◽

X Ray ◽

Cluster Mass ◽

Low Mass ◽

Optical Identifications ◽

X Ray Binaries

AbstractLow-mass X-ray binaries, recycled pulsars, cataclysmic variables and magnetically active binaries are observed as X-ray sources in globular clusters. We discuss the classification of these systems, and find that some presumed active binaries are brighter than expected. We discuss a new statistical method to determine from observations how the formation of X-ray sources depends on the number of stellar encounters and/or on the cluster mass. We show that cluster mass is not a proxy for the encounter number, and that optical identifications are essential in proving the presence of primordial binaries among the low-luminosity X-ray sources.

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