The “dynamical clock”: dating the internal dynamical evolution of star clusters with Blue Straggler Stars

Ferraro, F. R.; Lanzoni, B.; Dalessandro, E.

doi:10.1007/s12210-020-00873-2

Cited by 24 publications

(26 citation statements)

References 95 publications

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“…The comparison with the observations shows a general good agreement, both on the plane of the sky and along the line-of-sight direction, with the rotation curves obtained in advanced evolutionary phases of the N-body model, when the system has lost a significant fraction of its initial angular momentum. Hence, the cluster rotational properties suggest an old dynamical age for NGC 1904, in agreement with what is inferred from the radial distribution of blue straggler stars (see Ferraro et al 2012Ferraro et al , 2018bFerraro et al , 2020Lanzoni et al 2016). This study shows the importance of a complete 3D kinematic characterization of stellar systems.…”

Section: Discussionsupporting

confidence: 86%

“…and external effects in the environment in which they are embedded (e.g., Galactic tides, disk shocks). In fact, in spite of their similar chronological ages (∼12 Gyr; Forbes & Bridges 2010), GGCs show different stages of internal dynamical evolution (see Ferraro et al 2020 and references therein) and therefore are ideal laboratories where the complex interplay between stellar population properties and dynamical evolutionary effects can be empirically investigated. The innermost core regions of GGCs are expected to offer the ideal environment for the occurrence of stellar interactions able to generate exotic objects, like interacting binaries, blue stragglers, millisecond pulsars (Bailyn 1995;;Ferraro et al 1997Ferraro et al , 2003Ferraro et al , 2018aPooley et al 2003;Ransom et al 2005), and even the longsought class of intermediate-mass black holes (IMBHs; e.g., Giersz et al 2015).…”

Section: Introductionmentioning

confidence: 99%

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The ESO-VLT MIKiS Survey Reloaded: Velocity Dispersion Profile and Rotation Curve of NGC 1904*

Leanza

Pallanca

Ferraro

et al. 2022

ApJ

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We present an investigation of the internal kinematic properties of M79 (NGC 1904). Our study is based on radial velocity measurements obtained from the ESO-VLT Multi-Instrument Kinematic Survey (MIKiS) of Galactic globular clusters for more than 1700 individual stars distributed between ∼0.″3 and 770″ (∼14 three-dimensional half-mass radii) from the center. Our analysis reveals the presence of ordered line-of-sight rotation with a rotation axis almost aligned along the east–west direction and a velocity peak of 1.5 km s−1 at ∼70″ from the rotation axis. The velocity dispersion profile is well described by the same King model that best fits the projected density distribution, with a constant central plateau at σ 0 ∼ 6 km s−1. To investigate the cluster rotation in the plane of the sky, we have analyzed the proper motions provided by the Gaia EDR3, finding a signature of rotation with a maximum amplitude of ∼2.0 km s−1 at ∼80″ from the cluster center. Analyzing the three-dimensional velocity distribution for a subsample of 130 stars, we confirm the presence of systemic rotation and find a rotation axis inclination angle of 37° with respect to the line of sight. As a final result, the comparison of the observed rotation curves with the results of a representative N-body simulation of a rotating star cluster shows that the present-day kinematic properties of NGC 1904 are consistent with those of a dynamically old system that has lost a significant fraction of its initial angular momentum.

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Section: Discussionsupporting

confidence: 86%

Section: Introductionmentioning

confidence: 99%

The ESO-VLT MIKiS Survey Reloaded: Velocity Dispersion Profile and Rotation Curve of NGC 1904*

Leanza

Pallanca

Ferraro

et al. 2022

ApJ

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“…The advanced stage of dynamical evolution of this system is further certified by the high radial concentration of its blue straggler stars (seeLanzoni et al 2016;Ferraro et al 2018), which is a powerful indicator of dynamical age (the "dynamical clock"; seeFerraro et al 2012Ferraro et al , 2018Ferraro et al , 2019Ferraro et al , 2020.…”

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confidence: 99%

Slowly Cooling White Dwarfs in NGC 6752

Chen¹,

Ferraro²,

Cadelano³

et al. 2022

ApJ

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Recently, a new class of white dwarfs (“slowly cooling WDs”) has been identified in the globular cluster M13. The cooling time of these stars is increased by stable thermonuclear hydrogen burning in their residual envelope. These WDs are thought to be originated by horizontal branch (HB) stars populating the HB blue tail that skipped the asymptotic giant branch phase. To further explore this phenomenon, we took advantage of deep photometric data acquired with the Hubble Space Telescope in the near-ultraviolet and investigate the bright portion of the WD cooling sequence in NGC 6752, another Galactic globular cluster with a metallicity, age, and HB morphology similar to M13. The normalized WD luminosity function derived in NGC 6752 turns out to be impressively similar to that observed in M13, in agreement with the fact that the stellar mass distribution along the HB of these two systems is almost identical. As in the case of M13, the comparison with theoretical predictions is consistent with ∼70% of the investigated WDs evolving at slower rates than standard, purely cooling WDs. Thanks to its relatively short distance from Earth, NGC 6752 photometry reaches a luminosity 1 order of a magnitude fainter than the case of M13, allowing us to sample a regime where the cooling time delay, with respect to standard WD models, reaches ∼300 Myr. The results presented in this paper provide new evidence for the existence of slowly cooling WDs and further support to the scenario proposing a direct causal connection between this phenomenon and the HB morphology of the host stellar cluster.

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“…It quantifies the timescale needed by two-body interactions (causing kinetic-energy exchanges among stars) to bring the cluster toward a thermodynamically relaxed state. This quantity has been used to validate the so-called A + parameter, quantifying the level of central segregation of blue straggler stars within a GC (Alessandrini et al 2016), as a powerful empirical diagnostic of the dynamical age of the host system (e.g., Ferraro et al 2018aFerraro et al , 2019Lanzoni et al 2016;Ferraro et al 2020). Primarily depending on the local density, the value of the relaxation time changes with the radial distance from the cluster center.…”

Section: Discussionmentioning

confidence: 99%

A new identity card for the bulge globular cluster NGC 6440 from resolved star counts

Pallanca,

Lanzoni,

Ferraro

et al. 2021

Preprint

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We present a new identity card for the cluster NGC 6440 in the Galactic Bulge. We have used a combination of high-resolution Hubble Space Telescope images, wide-field ground-based observations performed with the ESO-FORS2, and the public survey catalog Pan-STARRS, to determine the gravitational center, projected density profile and structural parameters of this globular from resolved star counts. The new determination of the cluster center differs by ∼ 2 ′′ (corresponding to 0.08 pc) from the previous estimate, which was based on the surface brightness peak. The star density profile, extending out to 700 ′′ from the center and suitably decontaminated from the Galactic field contribution, is bestfitted by a King model with significantly larger concentration (c = 1.86 ± 0.06) and smaller core radius (r c = 6.4 ′′ ± 0.3 ′′ ) with respect to the literature values. By taking advantage of high-quality optical and near-infrared color-magnitude diagrams, we also estimated the cluster age, distance and reddening. The luminosity of the RGB-bump was also determined. This study indicates that the extinction coefficient in the bulge, in the direction of the cluster has a value (R V = 2.7) that is significantly smaller than that traditionally used for the Galaxy (R V = 3.1). The corresponding best-fit values of the age, distance and color excess of NGC 6440 are 13 Gyr, 8.3 kpc and E(B − V ) ∼ 1.27, respectively. These new determinations also allowed us to update the values of the central (t rc = 2.5 10 7 yr) and half-mass (t rh = 10 9 yr) relaxation times, suggesting that NGC 6440 is in a dynamically evolved stage.

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The “dynamical clock”: dating the internal dynamical evolution of star clusters with Blue Straggler Stars

Cited by 24 publications

References 95 publications

The ESO-VLT MIKiS Survey Reloaded: Velocity Dispersion Profile and Rotation Curve of NGC 1904*

The ESO-VLT MIKiS Survey Reloaded: Velocity Dispersion Profile and Rotation Curve of NGC 1904*

Slowly Cooling White Dwarfs in NGC 6752

A new identity card for the bulge globular cluster NGC 6440 from resolved star counts

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