Do open star clusters evolve towards energy equipartition?

Spera, M.; Mapelli, Michela; Jeffries, R. D.

doi:10.1093/mnras/stw998

Cited by 40 publications

(40 citation statements)

References 74 publications

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“…For the Quintuplet, we assume a cluster mass of 2 × 10 4 M , a half-mass radius 2 of 1.4 pc, and an IMF consistent with local star forming regions for 0.08 M < M < 0.5 M (dN/dm ∝ m −1.3 ; Kroupa 2002), and the Arches cluster for M > 0.5 M (dN/dm ∝ m −1.8 ; Hosek et al 2019). This yields an overall half-mass relaxation time of ∼ 42 Myr and a relaxation time of ∼ 6 Myr for stars around 10 M (Spitzer 1987;Spera et al 2016;Angelo et al 2018). The corresponding calculation for the Arches yields an overall half-mass relaxation time of ∼ 13 Myr and a relaxation time of only ∼ 2 Myr for 10 M stars.…”

Section: Mass Segregation In Ymcsmentioning

confidence: 83%

The Quintuplet Cluster: Extended Structure and Tidal Radius

Rui

Hosek

et al. 2019

ApJ

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The Quintuplet star cluster is one of only three known young (< 10 Myr) massive (M > 10 4 M ) clusters within ∼ 100 pc of the Galactic Center. In order to explore star cluster formation and evolution in this extreme environment, we analyze the Quintuplet's dynamical structure. Using the HST WFC3-IR instrument, we take astrometric and photometric observations of the Quintuplet covering a 120 × 120 field-of-view, which is 19 times larger than those of previous proper motion studies of the Quintuplet. We generate a catalog of the Quintuplet region with multi-band, near-infrared photometry, proper motions, and cluster membership probabilities for 10, 543 stars. We present the radial density profile of 715 candidate Quintuplet cluster members with M 4.7 M out to 3.2 pc from the cluster center. A 3σ lower limit of 3 pc is placed on the tidal radius, indicating the lack of a tidal truncation within this radius range. Only weak evidence for mass segregation is found, in contrast to the strong mass segregation found in the Arches cluster, a second and slightly younger massive cluster near the Galactic Center. It is possible that tidal stripping hampers a mass segregation signature, though we find no evidence of spatial asymmetry. Assuming that the Arches and Quintuplet formed with comparable extent, our measurement of the Quintuplet's comparatively large core radius of 0.62 +0.10 −0.10 pc provides strong empirical evidence that young massive clusters in the Galactic Center dissolve on a several Myr timescale.

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Section: Mass Segregation In Ymcsmentioning

confidence: 83%

The Quintuplet Cluster: Extended Structure and Tidal Radius

Rui

Hosek

et al. 2019

ApJ

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“…It is currently unknown as to whether mass segregation is due to some facet of the star formation process (e.g., Bonnell & Davies 1998), whether it can be rapidly induced through dynamical interactions (e.g., Allison et al 2009), or 5 Note that not all self-gravitating systems can attain complete energy equipartition (Spitzer 1969;Trenti & van der Marel 2013). whether the two processes can develop independently (e.g., Spera et al 2016).…”

Section: Velocity Dispersions As a Function Of Stellar Massmentioning

confidence: 99%

Cygnus OB2 DANCe: A high-precision proper motion study of the Cygnus OB2 association

Wright

Bouy

Drew

et al. 2016

Mon. Not. R. Astron. Soc.

127

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We present a high-precision proper motion study of 873 X-ray and spectroscopically selected stars in the massive OB association Cygnus OB2 as part of the DANCe project. These were calculated from images spanning a 15 year baseline and have typical precisions < 1 mas/yr. We calculate the velocity dispersion in the two axes to be σ α (c) = 13.0 +0.8 −0.7 and σ δ (c) = 9.1 +0.5 −0.5 km s −1 , using a 2-component, 2-dimensional model that takes into account the uncertainties on the measurements. This gives a 3-dimensional velocity dispersion of σ 3D = 17.8 ± 0.6 km s −1 implying a virial mass significantly larger than the observed stellar mass, confirming that the association is gravitationally unbound. The association appears to be dynamically unevolved, as evidenced by considerable kinematic substructure, non-isotropic velocity dispersions and a lack of energy equipartition. The proper motions show no evidence for a global expansion pattern, with approximately the same amount of kinetic energy in expansion as there is in contraction, which argues against the association being an expanded star cluster disrupted by process such as residual gas expulsion or tidal heating. The kinematic substructures, which appear to be close to virial equilibrium and have typical masses of 40-400 M ⊙ , also do not appear to have been affected by the expulsion of the residual gas. We conclude that Cyg OB2 was most likely born highly substructured and globally unbound, with the individual subgroups born in (or close to) virial equilibrium, and that the OB association has not experienced significant dynamical evolution since then.

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“…Correspondingly, the velocity dispersion and spatial extent of lighter-than-average stars increases. Complete energy equipartion is never reached (see Trenti & van der Marel 2013;Bianchini et al 2016;Spera et al 2016) because GCs are open systems -stars that gain too much energy become unbound. The two-body relaxation time (which has a median value of ≈ 10 8 yr for galactic GCs; Heggie & Hut 2003) is the relevant time-scale over which globular clusters undergo mass segregation, and it depends primarily on mass and radius, with compact low-mass clusters characterized by shorter relaxation times compared to extended and highmass counterparts.…”

Section: Introductionmentioning

confidence: 99%

Correlation between mass segregation and structural concentration in relaxed stellar clusters

Vita

Trenti

MacLeod

2019

Monthly Notices of the Royal Astronomical Society

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The level of mass segregation in the core of globular clusters has been previously proposed as a potential indicator of the dynamical constituents of the system, such as presence of a significant population of stellar-mass black holes (BHs), or even a central intermediate-mass black hole (IMBH). However, its measurement is limited to clusters with high-quality Hubble Space Telescope data. Thanks to a set of state-of-the-art direct N-body simulations with up to 200k particles inclusive of stellar evolution, primordial binaries, and varying BH/neutron stars, we highlight for the first time the existence of a clear and tight linear relation between the degree of mass segregation and the cluster structural concentration index. The latter is defined as the ratio of the radii containing 5% and 50% of the integrated light (R 5 /R 50 ), making it robustly measurable without the need to individually resolve low-mass stars. Our simulations indicate that given R 5 /R 50 , the mass segregation ∆m (defined as the difference in main sequence median mass between center and half-light radius) is expressed as ∆m/M = −1.166R 5 /R h + 0.3246, with a root-mean-square error of 0.0148. In addition, we can explain its physical origin and the values of the fitted parameters through basic analytical modeling. Such correlation is remarkably robust against a variety of initial conditions (including presence of primordial binaries and IMBHs) and cluster ages, with a slight dependence in best-fit parameters on the prescriptions used to measure the quantities involved. Therefore, this study highlights the potential to develop a new observational tool to gain insight on the dynamical status of globular clusters and on its dark remnants.

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Do open star clusters evolve towards energy equipartition?

Cited by 40 publications

References 74 publications

The Quintuplet Cluster: Extended Structure and Tidal Radius

The Quintuplet Cluster: Extended Structure and Tidal Radius

Cygnus OB2 DANCe: A high-precision proper motion study of the Cygnus OB2 association

Correlation between mass segregation and structural concentration in relaxed stellar clusters

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