The Structure of Globular Clusters

Djorgovski, S. G.; King, Ivan R.; Vuosalo, C.; Oren, A. L.; Penner, Hans H.

doi:10.1007/978-94-010-9433-7_53

Cited by 15 publications

(13 citation statements)

References 1 publication

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“…Besides the different definitions, all these normalisations account for the different cluster richness (i.e, total luminosity or mass). However, as discussed in [23], particular caution is needed when looking for correlations among BSS specific frequencies and cluster structural parameters, since the concentration parameter and central density are intrinsically related to the cluster luminosity (see, e.g., [18]); hence spurious correlations can emerge simply because of the BSS "normalisation".…”

Section: Bss Specific Frequency and Primordial Binary Fractionmentioning

confidence: 99%

Blue Straggler Stars in Globular Clusters: A Powerful Tool to Probe the Internal Dynamical Evolution of Stellar Systems

Ferraro¹,

Lanzoni²,

Dalessandro³

et al. 2014

Ecology of Blue Straggler Stars

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Blue straggler stars (BSSs) in globular clusters (GCs) are commonly defined as those stars located along an extrapolation of the main sequence (MS), in a region brighter and bluer (hotter) than the turnoff (TO) point, in the optical colourmagnitude diagram (CMD; see Fig. 5.1). They were first discovered by Sandage [70] in the external region of the Galactic GC M3. Their origin has been a mystery for many years and the puzzle of their formation is not completely solved yet.The BSS location in the CMD suggests that they are more massive than the current cluster population ( Fig. 5.1; this is also confirmed by a few mass measurements, e.g., [74,35]). However, GCs are completely devoid of gas and any recent star formation event can be realistically ruled out. Hence the BSS origin should be searched in some mechanisms able to increase the initial mass of single stars in a sort of rejuvenation process. The BSS formation mechanisms are not completely understood yet, but the main leading scenarios, at present, are mass transfer (MT) processes between binary companions [58,82], possibly up to the complete coalescence of the binary system, or the merger of stars induced by collisions (COLL; [37]). Being more massive than the average cluster stars, BSSs suffer from the effect of dynamical friction, that makes them sink towards the cluster centre [53,32]. In turn, the frequent stellar interactions occurring in the ultra-dense cores of Galactic GCs can promote both the formation and the hardening of binary systems, thus contributing to generate MT-BSSs. All these considerations clearly show that BSSs represent a crucial link between standard stellar evolution and GC internal dynamics (see [3,32], and references therein).

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Section: Bss Specific Frequency and Primordial Binary Fractionmentioning

confidence: 99%

Blue Straggler Stars in Globular Clusters: A Powerful Tool to Probe the Internal Dynamical Evolution of Stellar Systems

Ferraro¹,

Lanzoni²,

Dalessandro³

et al. 2014

Ecology of Blue Straggler Stars

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“…However, other clues complicate the picture. For example, the unusually high ellipticity of ω Cen, which has been demonstrated to be sustained by rotation (Merritt & Tremblay 1994), is compatible with the flattened shapes resulting from the merger of two globular clusters (Makino, Akiyama & Sugimoto 1991), and anyway the long relaxation time (Djorgovski 1993; Merritt, Meylan & Mayor 1997) grants that ω Centauri is not completely relaxed dynamically. Moreover, Norris et al (1997) showed that only stars with [Fe/H]≤−1.2 in ω Cen do rotate, while the more metal‐rich components show no evident sign of rotation.…”

Section: Introductionmentioning

confidence: 97%

The multiple stellar population in omega Centauri: spatial distribution and structural properties

Pancino

Seleznev

Ferraro

et al. 2003

Monthly Notices RAS

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We present a detailed analysis of the spatial distribution of the stellar populations in the Galactic globular cluster ω Centauri. Taking advantage of the large photometric catalogue published by Pancino et al., we confirm that metal‐rich populations have a spatial distribution which is significantly different from the metal‐poor dominant population. In particular (i) the different sub‐populations have different centroids and (ii) the metal‐poor population is elongated along the east–west direction, while the metal‐rich populations are oriented along the orthogonal direction, i.e. north–south. The evidence presented here can partially explain the weird spatial metallicity segregation found by Jurcsik, and further supports the hypothesis that different subpopulations in ω Centauri might have had different origins.

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“…Because star clusters are collisionsdominated systems, we have a relatively advanced understanding of the distribution of their stars in phase space from theory and numerical simulations, and the choice of distribution function-based models is justified. The most popular model of this kind is the King (1966) model which proved to be quite effective in reproducing the surface brightness profiles of many GCs, open clusters and dwarf galaxies (Djorgovski 1993;McLaughlin & van der Marel 2005;CarballoBello et al 2012;Miocchi et al 2013). A generalization of this model accounting for radial anisotropy and a degree of equipartition among an arbitrary number of mass components has been provided by Gunn & Griffin (1979;see also Da Costa & Freeman 1976;Merritt 1981).…”

Section: Introductionmentioning

confidence: 99%

Testing multimass dynamical models of star clusters with real data: mass segregation in three Galactic globular clusters

Sollima

Dalessandro

Beccari

et al. 2016

Mon. Not. R. Astron. Soc.

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We present the results of the analysis of deep photometric data for a sample of three Galactic globular clusters (NGC5466, NGC6218 and NGC 6981) with the aim of estimating their degree of mass segregation and testing the predictions of analytic dynamical models. The adopted dataset, composed by both Hubble Space Telescope and ground based data, reaches the low-mass end of the mass functions of these clusters from the center up to their tidal radii allowing to derive their radial distribution of stars with different masses. All the analysed clusters show evidence of mass segregation with the most massive stars more concentrated than low-mass ones. The structures of NGC5466 and NGC6981 are well reproduced by multimass dynamical models adopting a lowered-Maxwellian distribution function and the prescription for mass segregation given by Gunn & Griffin (1979). Instead, NGC6218 appears to be more mass segregated than model predictions. By applying the same technique to mock observations derived from snapshots selected from suitable N-body simulations we show that the deviation from the behaviour predicted by these models depends on the particular stage of dynamical evolution regardless of initial conditions.

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The Structure of Globular Clusters

Cited by 15 publications

References 1 publication

Blue Straggler Stars in Globular Clusters: A Powerful Tool to Probe the Internal Dynamical Evolution of Stellar Systems

Blue Straggler Stars in Globular Clusters: A Powerful Tool to Probe the Internal Dynamical Evolution of Stellar Systems

The multiple stellar population in omega Centauri: spatial distribution and structural properties

Testing multimass dynamical models of star clusters with real data: mass segregation in three Galactic globular clusters

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