The globular cluster NGC 6642: evidence for a depleted mass function

2009 ◽  
Vol 5 (S266) ◽  
pp. 357-360
Author(s):  
Eduardo Balbinot ◽  
Basílio X. Santiago ◽  
Eduardo Bica ◽  
Charles Bonatto
Keyword(s):  
Globular Cluster ◽  
Globular Clusters ◽  
Hubble Space Telescope ◽  
Dynamical Evolution ◽  
Mass Function ◽  
Galactic Centre ◽  
Low Mass Stars ◽  
Current Location ◽  
Mass Segregation ◽  
High Level

AbstractWe present photometry for the globular cluster NGC 6642 using the F606W and F814W filters with the ACS/WFC third-generation camera aboard the Hubble Space Telescope. The colour–magnitude diagram shows sources reaching ≈ 6 mag below the turnoff in mF606W. Theoretical isochrone fitting was performed and evolutionary parameters were obtained, including the metallicity [Fe/H] = −1.80 ± 0.2 dex and age, log(age/yr) = 10.14 ± 0.05. We confirm that NGC 6642 is located in the Galactic bulge, at a distance of d⊙ = 8.05±0.66 kpc and suffers from a reddening of E(B − V) = 0.46 ± 0.02 mag. These values are in general agreement with those of previous authors. Completeness-corrected luminosity and mass functions were obtained for different annuli centred on NGC 6642. Their spatial variation indicates the existence of mass segregation and depletion of low-mass stars. Most striking is the inverted shape of the mass function itself, with an increase in stellar numbers as a function of increasing mass. This has been observed previously in other globular clusters and is also the result of N-body simulations of stellar systems which have reached ≃90% of their lifetime and are subjected to strong tidal effects. We thus conclude that NGC 6642 is a very old, highly evolved globular cluster. Its current location close to perigalacticon, at only 1.4 kpc from the Galactic Centre, may contribute to this high level of dynamical evolution and stellar depletion.

scholarly journals Radial variation of the stellar mass functions in the globular clusters M15 and M30: clues of a non-standard IMF?

2020 ◽  
Vol 499 (2) ◽  
pp. 2390-2400
Author(s):  
M Cadelano ◽  
E Dalessandro ◽  
J J Webb ◽  
E Vesperini ◽  
D Lattanzio ◽  
...  
Keyword(s):  
Globular Clusters ◽  
Hubble Space Telescope ◽  
Dynamical Evolution ◽  
Mass Function ◽  
Initial Mass Function ◽  
Radial Variation ◽  
Wide Field ◽  
Data Set ◽  
Central Regions ◽  
Mass Segregation

ABSTRACT We exploit a combination of high-resolution Hubble Space Telescope and wide-field ESO-VLT observations to study the slope of the global mass function (αG) and its radial variation (α(r)) in the two dense, massive and post core-collapse globular clusters M15 and M30. The available data set samples the clusters’ main sequence down to ∼0.2 M⊙ and the photometric completeness allows the study of the mass function between 0.40 M⊙ and 0.75 M⊙ from the central regions out to their tidal radii. We find that both clusters show a very similar variation in α(r) as a function of clustercentric distance. They both exhibit a very steep variation in α(r) in the central regions, which then attains almost constant values in the outskirts. Such a behaviour can be interpreted as the result of long-term dynamical evolution of the systems driven by mass-segregation and mass-loss processes. We compare these results with a set of direct N-body simulations and find that they are only able to reproduce the observed values of α(r) and αG at dynamical ages (t/trh) significantly larger than those derived from the observed properties of both clusters. We investigate possible physical mechanisms responsible for such a discrepancy and argue that both clusters might be born with a non-standard (flatter/bottom-lighter) initial mass function.

scholarly journals Dynamical Evolution of Outer-Halo Globular Clusters

2015 ◽  
Vol 12 (S316) ◽  
pp. 257-258
Author(s):  
Andreas H. W. Küpper ◽  
Akram H. Zonoozi ◽  
Hosein Haghi ◽  
Nora Lützgendorf ◽  
Steffen Mieske ◽  
...  
Keyword(s):  
Globular Clusters ◽  
Milky Way ◽  
Dynamical Evolution ◽  
Mass Function ◽  
Low Mass Stars ◽  
Central Mass ◽  
The Past ◽  
Main Driver ◽  
Mass Segregation ◽  
Mass Functions

AbstractOuter-halo globular clusters show large half-light radii and flat stellar mass functions, depleted in low-mass stars. Using N-body simulations of globular clusters on eccentric orbits within a Milky Way-like potential, we show how a cluster’s half-mass radius and its mass function develop over time. The slope of the central mass function flattens proportionally to the amount of mass a cluster has lost, and the half-mass radius grows to a size proportional to the average strength of the tidal field. The main driver of these processes is mass segregation of dark remnants. We conclude that the extended, depleted clusters observed in the Milky Way must have had small half-mass radii in the past, and that they expanded due to the weak tidal field they spend most of their lifetime in. Moreover, their mass functions must have been steeper in the past but flattened significantly as a cause of mass segregation and tidal mass loss.

Dynamical Evolution of Globular Clusters with Mass Spectrum

1991 ◽  
Vol 9 (1) ◽  
pp. 41-44
Author(s):  
Hyung Mok Lee
Keyword(s):  
Mass Spectrum ◽  
Globular Clusters ◽  
Numerical Models ◽  
Relaxation Times ◽  
Dynamical Evolution ◽  
Planck Equation ◽  
Mass Function ◽  
Low Mass Stars ◽  
Wide Range ◽  
Three Body

AbstractWe present a series of numerical models describing the dynamical evolution of globular clusters with a mass spectrum, based on integration of the Fokker-Planck equation. We include three-body binary heating and a steady galactic tidal field. A wide range of initial mass functions is adopted and the evolution of the mass function is examined. The mass function begins to change appreciably during the post-collapse expansion phase due to the selective evaporation of low mass stars through the tidal boundary. One signature of highly evolved clusters is thus the significant flattening of the mass function. The age (in units of the half-mass relaxation time) increases very rapidly beyond about 100 signifying the final stage of cluster disruption. This appears to be consistent with the sharp cut-off of half-mass relaxation times at near 108 years for the Galactic globular clusters.

scholarly journals Observational Constraints on the Formation and Evolution of Globular Cluster Systems

2007 ◽  
Vol 3 (S246) ◽  
pp. 394-402
Author(s):  
Stephen E. Zepf
Keyword(s):  
Globular Cluster ◽  
Globular Clusters ◽  
Dynamical Evolution ◽  
Mass Function ◽  
Cluster System ◽  
Host Galaxy ◽  
Cluster Systems ◽  
Cluster Mass ◽  
Formation And Evolution ◽  
Globular Cluster System

AbstractThis paper reviews some of the observational properties of globular cluster systems, with a particular focus on those that constrain and inform models of the formation and dynamical evolution of globular cluster systems. I first discuss the observational determination of the globular cluster luminosity and mass function. I show results from new very deep HST data on the M87 globular cluster system, and discuss how these constrain models of evaporation and the dynamical evolution of globular clusters. The second subject of this review is the question of how to account for the observed constancy of the globular cluster mass function with distance from the center of the host galaxy. The problem is that a radial trend is expected for isotropic cluster orbits, and while the orbits are observed to be roughly isotropic, no radial trend in the globular cluster system is observed. I review three extant proposals to account for this, and discuss observations and calculations that might determine which of these is most correct. The final subject is the origin of the very weak mass-radius relation observed for globular clusters. I discuss how this strongly constrains how globular clusters form and evolve. I also note that the only viable current proposal to account for the observed weak mass-radius relation naturally effects the globular cluster mass function, and that these two problems may be closely related.

scholarly journals Correlation between mass segregation and structural concentration in relaxed stellar clusters

2019 ◽  
Vol 485 (4) ◽  
pp. 5752-5760 ◽  
Author(s):  
Ruggero de Vita ◽  
Michele Trenti ◽  
Morgan MacLeod
Keyword(s):  
Globular Clusters ◽  
Initial Conditions ◽  
Hubble Space Telescope ◽  
Stellar Clusters ◽  
Low Mass Stars ◽  
Best Fitting ◽  
Low Mass ◽  
The Difference ◽  
Mass Segregation ◽  
First Time

Abstract 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 per cent and 50 per cent of the integrated light (R5/R50), making it robustly measurable without the need to individually resolve low-mass stars. Our simulations indicate that given R5/R50, the mass segregation Δm (defined as the difference in main-sequence median mass between centre and half-light radius) is expressed as Δm/M⊙ = −1.166R5/R50 + 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 modelling. 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-fitting 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.

scholarly journals Globular Clusters: Low Mass Stars, Still No Brown Dwarfs!

2003 ◽  
Vol 211 ◽  
pp. 215-222
Author(s):  
Guido De Marchi
Keyword(s):  
Globular Clusters ◽  
Functional Form ◽  
Dynamical Evolution ◽  
Mass Function ◽  
Brown Dwarf ◽  
Low Mass Stars ◽  
Homogeneous Sample ◽  
Original Mass ◽  
Low Mass ◽  
The Imf

In spite of all the attempts to find them, no one has yet detected any brown dwarf in a globular cluster. Although powerful instruments such as the VLT and Advanced Camera could further push the frontiers of this search, globular clusters will probably hold tight to their secrets for a while longer. Nonetheless, the search for very low mass stars in globular clusters has taught us a lot about their original mass distribution (IMF) and its evolution in time. I shall review the results of an investigation carried out over what is presently the largest, most homogeneous sample, and discuss the reasons suggesting that: 1. dynamical evolution (internal and external) has reshaped the cluster mass function over time, but the imprint of the IMF is still visible; 2. the IMF appears to vary very little from cluster to cluster; 3. the most likely functional form of the IMF is that of a power law that rises to a peak at ˜ 0.3 M⊙ and tapers off at smaller masses.

scholarly journals Dynamical Evolution of the Mass Function of the Globular Cluster System from Fokker-Planck Calculations: Preliminary Results

2006 ◽  
Vol 2 (S235) ◽  
pp. 110-110
Author(s):  
Jihye Shin ◽  
Sungsoo S. Kim
Keyword(s):  
Stellar Evolution ◽  
Globular Cluster ◽  
Globular Clusters ◽  
Dynamical Evolution ◽  
Mass Function ◽  
Cluster System ◽  
Dynamical Friction ◽  
Luminosity Functions ◽  
Globular Cluster System ◽  
Fokker Planck

AbstractUsing anisotropic Fokker-Planck models, we calculate the evolution of mass and luminosity functions of the Galactic globular cluster system. Our models include two-body relaxation, binary heating, tidal shocks, dynamical friction, and stellar evolution. We perform Fokker-Planck simulations for a large number of virtual globular clusters and synthesize these results to study the relation between the initial and present GCMFs.

scholarly journals Blue Stragglers in the Core of the Globular Cluster 47 Tucanae

1992 ◽  
Vol 9 ◽  
pp. 451-453
Author(s):  
G. Meylan ◽  
F. Paresce ◽  
M. Shara
Keyword(s):  
Globular Cluster ◽  
Globular Clusters ◽  
Hubble Space Telescope ◽  
High Surface ◽  
Blue Stragglers ◽  
The Core ◽  
Faint Object ◽  
Resolution Imaging ◽  
Mass Segregation ◽  
Very High

AbstractHigh resolution imaging observations of the core of the globular cluster 47 Tucanae with the Faint Object Camera (FOC) on the Hubble Space Telescope (HST) reveal a very high surface density of blue stragglers. This discovery supports the hypothesis that they are among the most massive objects in globular clusters, concentrated in the core by mass segregation. Taken together with the presence in 47 Tue of an X-ray source, eleven millisecond and binary pulsars, and two high-velocity stars ejected out of the core, these observations favour the scenario that blue stragglers are either mergers formed through coalescent collisions, or binaries formed through close encounters.

scholarly journals Dynamical Implications of Deep HST Imaging of Globular Clusters

1996 ◽  
Vol 174 ◽  
pp. 29-38
Author(s):  
Ivan R. King
Keyword(s):  
Globular Clusters ◽  
Dynamical Evolution ◽  
Cluster Center ◽  
Core Collapse ◽  
Low Mass Stars ◽  
Dynamical Nature ◽  
Low Mass ◽  
Dense Cluster ◽  
Mass Segregation ◽  
Mass Functions

HST observations contribute in many ways to a better understanding of the dynamical nature of globular clusters. Unprecedentedly faint photometry gives new determinations of the numbers of low-mass stars. Cluster-to-cluster differences at the faint ends of the mass functions suggest differences in dynamical evolution. Mass segregation is clearly observed, from the envelope inward to the dense cluster center. The distribution of stars in the hitherto unresolved cores gives new data with which to test theories of core collapse, and these core profiles are also sensitive to the number of unseen remnant stars and binaries at the cluster center.

scholarly journals Dynamical Evolution of the Mass Function of the Galactic Globular Cluster System

2007 ◽  
Vol 3 (S246) ◽  
pp. 433-434
Author(s):  
Jihye Shin ◽  
Sungsoo S. Kim ◽  
Koji Takahashi
Keyword(s):  
Globular Cluster ◽  
Globular Clusters ◽  
Dynamical Evolution ◽  
Mass Function ◽  
Cluster System ◽  
Peak Mass ◽  
Low Mass ◽  
Globular Cluster System ◽  
Log Normal ◽  
Mass Functions

AbstractUsing the most advanced anisotropic (2D) Fokker-Planck (FP) models, we calculate the evolution of the mass functions of the Galactic globular cluster system (GCMF). Our models include two-body relaxation, binary heating, tidal shocks, dynamical friction, stellar evolution, and realistic cluster orbits. We perform 2D-FP simulations for a large number of virtual globular clusters and synthesize these results to study the relation between the initial and present GCMFs. We found two probable IGCMFs that eventually evolve into the Milky Way GCMF : truncated power-law, and log-normal model with higher initial low mass limit and peak mass than the earlier studies.

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