An empirical clock to measure the dynamical age of star clusters

2019 ◽  
Vol 14 (S351) ◽  
pp. 377-383
Author(s):  
Francesco R. Ferraro
Keyword(s):  
Radial Distribution ◽  
Special Class ◽  
Globular Clusters ◽  
Stellar Population ◽  
Star Clusters ◽  
Dynamical Evolution ◽  
Stellar Systems ◽  
Central Segregation ◽  
Blue Straggler ◽  
Definition Of

AbstractThe observational properties of a special class of stars (the so-called Blue Straggler stars - BSSs) in Globular Clusters are discussed in the framework of using this stellar population as probe of the dynamical processes occurring in high-density stellar systems. In particular, the shape of the BSS radial distribution and their level of central segregation have been found to be powerful tracers of the level of the dynamical evolution of the hosting cluster, thus allowing the definition of an empirical chronometer able to measure the dynamical age of star clusters.

scholarly journals Exotic populations in globular clusters: blue stragglers as tracers of the internal dynamical evolution of stellar systems

2014 ◽  
Vol 10 (S312) ◽  
pp. 171-180
Author(s):  
Francesco R. Ferraro
Keyword(s):  
Radial Distribution ◽  
Globular Clusters ◽  
Stellar Population ◽  
Dynamical Evolution ◽  
Stellar Systems ◽  
Internal Dynamics ◽  
Blue Stragglers ◽  
Blue Straggler ◽  
Specific Frequency ◽  
Definition Of

AbstractIn this paper I present an overview of the main observational properties of a special class of exotic objects (the so-called Blue Straggler Stars, BSSs) in Galactic Globular Clusters (GCs). The BSS specific frequency and their radial distribution are discussed in the framework of using this stellar population as probe of GC internal dynamics. In particular, the shape of the BSS radial distribution has been found to be a powerful tracer of the dynamical evolution of stellar systems, thus allowing the definition of an empirical “clock”able to measure the dynamical age of stellar aggregates from pure observational properties.

scholarly journals The blue straggler population of the old open cluster Berkeley 17

2019 ◽  
Vol 624 ◽  
pp. A26 ◽  
Author(s):  
Souradeep Bhattacharya ◽  
Kaushar Vaidya ◽  
W. P. Chen ◽  
Giacomo Beccari
Keyword(s):  
Radial Distribution ◽  
Globular Clusters ◽  
Minimum Spanning Tree ◽  
Open Cluster ◽  
Dynamical Evolution ◽  
Open Clusters ◽  
Blue Straggler ◽  
Magnitude Diagram ◽  
First Time ◽  
Giant Branch Stars

Context. Blue straggler stars (BSSs) are observed in Galactic globular clusters and old open clusters. The radial distribution of BSSs has been used to diagnose the dynamical evolution of globular clusters. For the first time, with a reliable sample of BSSs identified with Gaia DR2, we conduct such an analysis for an open cluster. Aims. We aim to identify members, including BSSs, of the oldest known Galactic open cluster Berkeley 17 with the Gaia DR2 proper motions and parallaxes. We study the radial distribution of the BSS population to understand the dynamical evolution of the cluster. Methods. We selected cluster members to populate the colour magnitude diagram in the Gaia filters. Cluster parameters are derived using the brightest members. The BSSs and giant branch stars are identified, and their radial distributions are compared. The segregation of BSSs is also evaluated with respect to the giant branch stars using the minimum spanning tree (MST) analysis. Results. We determine Berkeley 17 to be at 3138.6−352.9+285.5 pc. We find 23 BSS cluster members, only two of which were previously identified. We find a bimodal radial distribution of BSSs supported by findings from the MST method. Conclusions. The bimodal radial distribution of BSSs in Berkeley 17 indicates that they have just started to sink towards the cluster centre, placing Berkeley 17 with globular clusters of intermediate dynamical age. This is the first such determination for an open cluster.

scholarly journals Blue Stragglers: Spectra of Globular Clusters

2009 ◽  
Vol 5 (S262) ◽  
pp. 23-26
Author(s):  
A. J. Cenarro ◽  
J. L. Cervantes ◽  
M. A. Beasley ◽  
A. Marin-Franch ◽  
A. Vazdekis
Keyword(s):  
Globular Clusters ◽  
Stellar Population ◽  
Main Sequence ◽  
Stellar Systems ◽  
Blue Stragglers ◽  
Horizontal Branch Stars ◽  
Blue Straggler ◽  
Balmer Lines ◽  
Specific Frequency ◽  
High Metallicity

AbstractThe integrated Balmer lines of unresolved stellar systems have been widely used as age indicators, since they are sensitive to the temperature of the main sequence turn-off. However, the existence of “non-canonical” stellar stages such as hot horizontal branch stars and blue straggler stars (BSSs) can lead to underestimations of the true stellar population ages. Using an optimized Hβ index in conjunction with HST/WFPC2 color-magnitude diagrams (CMDs), we find that Galactic globular clusters of similar metallicity exhibit a large scatter in their Hβ strengths, which does not correlate with their CMD-derived ages. Instead, we demonstrate that the specific frequency of BSSs is responsible for the observed Hβ scatter at intermediate-to-high metallicity, in the sense that, at fixed metallicity, higher BSS ratios lead to larger integrated Hβ strengths. Therefore, the specific frequency of BSSs sets a fundamental limit on the accuracy for which integrated spectroscopic ages can be determined for globular clusters and, probably, other stellar systems like galaxies. The observational implications of this result are discussed.

Phase space complexity of star clusters: Fresh observables for old and new questions

2019 ◽  
Vol 14 (S351) ◽  
pp. 389-394
Author(s):  
Anna Lisa Varri ◽  
Philip G. Breen ◽  
Douglas C. Heggie
Keyword(s):  
Phase Space ◽  
Globular Clusters ◽  
Star Clusters ◽  
Stellar Dynamics ◽  
Stellar Systems ◽  
Internal Dynamics ◽  
The Rich ◽  
Evolving Context ◽  
New Generation ◽  
Precision Astrometry

AbstractThe blooming era of precision astrometry for Galactic studies truly brings the rich internal dynamics of globular clusters to the centre stage. But several aspects of our current understanding of fundamental collisional stellar dynamics cannot match such new-generation data and the theoretical ambitions they trigger. This rapidly evolving context offers the stimulus to address a number of old and new questions concerning the phase space properties of this class of stellar systems.

scholarly journals Observed Variations in the Density Profiles of Star Clusters in the LMC

1988 ◽  
Vol 126 ◽  
pp. 571-572 ◽  
Author(s):  
M. Kontizas ◽  
D. Hatzidimitriou ◽  
M. Metaxa
Keyword(s):  
Observational Data ◽  
Star Clusters ◽  
Dynamical Evolution ◽  
Stellar Systems ◽  
Density Profiles ◽  
Valuable Source ◽  
Dynamical Properties ◽  
Source Of Information

Several dynamical theories have been developed in order to approach the dynamical evolution of stellar systems and explain the observational data. The observed density profiles of the clusters can be a valuable source of information towards the understanding of their dynamical properties. King in a series of papers has connected the established theories with the observed profiles in clusters of our own Galaxy (King, 1962, 1966; etc.). Density profiles can be obtained by means of star counts and/or by means of photometric photometry. So far the observations for clusters in our Galaxy and the MCs appear to fit well the so called King models and provide information of their tidal radii, total masses and concentration parameters (Kontizas, 1984).

scholarly journals Spectroscopic study of formation, evolution and interaction of M31 and M33 with star clusters

2014 ◽  
Vol 10 (S312) ◽  
pp. 201-202 ◽  
Author(s):  
Zhou Fan ◽  
Yanbin Yang
Keyword(s):  
Globular Clusters ◽  
Stellar Population ◽  
Local Group ◽  
Spiral Galaxies ◽  
Star Clusters ◽  
Star Cluster ◽  
Physical Parameters ◽  
Cluster Systems ◽  
Nearby Galaxies ◽  
Formation And Evolution

AbstractThe recent studies show that the formation and evolution process of the nearby galaxies are still unclear. By using the Canada France Hawaii Telescope (CFHT) 3.6m telescope, the PanDAS shows complicated substructures (dwarf satellite galaxies, halo globular clusters, extended clusters, star streams, etc.) in the halo of M31 to ~150 kpc from the center of galaxy and M31-M33 interaction has been studied. In our work, we would like to investigate formation, evolution and interaction of M31 and M33, which are the nearest two spiral galaxies in Local Group. The star cluster systems of the two galaxies are good tracers to study the dynamics of the substructures and the interaction. Since 2010, the Xinglong 2.16m, Lijiang 2.4m and MMT 6.5m telescopes have been used for our spectroscopic observations. The radial velocities and Lick absorption-line indices can thus be measured with the spectroscopy and then ages, metallicities and masses of the star clusters can be fitted with the simple stellar population models. These parameters could be used as the input physical parameters for numerical simulations of M31-M33 interaction.

scholarly journals Dynamical Evolution of Rotating Globular Clusters with Embedded Black Holes

2007 ◽  
Vol 3 (S246) ◽  
pp. 166-170
Author(s):  
J. Fiestas ◽  
O. Porth ◽  
R. Spurzem
Keyword(s):  
Black Holes ◽  
Black Hole ◽  
Globular Clusters ◽  
Dynamical Evolution ◽  
Momentum Transport ◽  
Stellar Systems ◽  
Angular Momentum Transport ◽  
Zone Of Influence ◽  
Velocity Diffusion ◽  
Parent Galaxy

AbstractEvolution of self-gravitating rotating dense stellar systems (e.g. globular clusters) with embedded black holes is investigated. The interplay between velocity diffusion due to relaxation and black hole star accretion is followed together with cluster differential rotation using 2D+1 Fokker Planck numerical methods. The models can reproduce the Bahcall-Wolf f ∝ E1/4 (∝ r−7/4) cusp inside the zone of influence of the black hole. Angular momentum transport and star accretion processes support the development of central rotation in relaxation time scales, before re-expansion and cluster dissolution due to mass loss in the tidal field of a parent galaxy. Gravogyro and gravothermal instabilities conduce the system to a faster evolution leading to shorter collapse times with respect to models without black hole.

scholarly journals Observations of blue straggler stars in globular clusters

2006 ◽  
Vol 2 (14) ◽  
pp. 438-439
Author(s):  
Francesco R. Ferraro ◽  
Barbara Lanzoni
Keyword(s):  
Globular Clusters ◽  
Binary Systems ◽  
Stellar Population ◽  
Main Sequence ◽  
Formation Mechanisms ◽  
Main Sequence Stars ◽  
Blue Stragglers ◽  
Photometric And Spectroscopic Observations ◽  
Blue Straggler ◽  
Dynamical Simulations

AbstractBlue stragglers stars (BSS) define a sparsely populated sequence extending to higher luminosity than the turnoff point of normal main sequence stars in the color magnitude diagrams of stellar aggregates, thus mimicking a rejuvenated (more massive) stellar population. The nature of these stars has been a puzzle for many years and their formation mechanism is not completely understood, yet. Two mechanisms have been proposed to produce BSS: (i) the mass transfer in binary systems; and ((ii) the merger of two stars induced by stellar interactions. In this contribution we schematically report on the main properties of BSS in globular clusters (GCs) in the light of the most recent photometric and spectroscopic observations. These results, combined with dynamical simulations, indicate that both the proposed formation mechanisms play an important role in the production of BSS in GCs.

scholarly journals The Influence of Gas Expulsion on the Evolution of Star Clusters

2007 ◽  
Vol 3 (S246) ◽  
pp. 36-40
Author(s):  
H. Baumgardt ◽  
P. Kroupa
Keyword(s):  
Globular Clusters ◽  
Milky Way ◽  
Three Dimensional ◽  
Star Clusters ◽  
Dynamical Evolution ◽  
Mass Function ◽  
Star Cluster ◽  
Dissolution Mechanism ◽  
Large Set ◽  
Cluster Systems

AbstractWe present new results on the dynamical evolution and dissolution of star clusters due to residual gas expulsion and the effect this has on the mass function and other properties of star cluster systems. To this end, we have carried out a large set of N-body simulations, varying the star formation efficiency, gas expulsion time scale and strength of the external tidal field, obtaining a three-dimensional grid of models which can be used to predict the evolution of individual star clusters or whole star cluster systems by interpolating between our runs. When applied to the Milky Way globular cluster system, we find that gas expulsion is the main dissolution mechanism for star clusters, destroying about 80% of all clusters within a few 10s of Myers. Together with later dynamical evolution, it seems possible to turn an initial power-law mass function into a log-normal one with properties similar to what has been observed for the Milky Way globular clusters.

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