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Mass segregation

About: Mass segregation is a research topic. Over the lifetime, 1024 publications have been published within this topic receiving 57729 citations.


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Journal ArticleDOI
TL;DR: In this article, an analysis of deep CCD photometry for the very rich, old open star cluster NGC 6819 is presented, where the authors find a tight, very rich main-sequence and turnoff consisting of over 2900 cluster stars in the V, B-V color-magnitude diagram (CMD).
Abstract: We present analysis of deep CCD photometry for the very rich, old open star cluster NGC 6819. The science goals are to catalog the white dwarfs in the cluster and measure the cluster luminosity and mass functions. These CFH12K data results represent the first of nineteen open star clusters which were imaged as a part of the CFHT Open Star Cluster Survey. We find a tight, very rich, main-sequence and turnoff consisting of over 2900 cluster stars in the V, B-V color-magnitude diagram (CMD). Main-sequence fitting of the unevolved cluster stars with the Hyades star cluster yields a distance modulus of (m - M)V = 12.30 ± 0.12, for a reddening of E(B-V) = 0.10. These values are consistent with a newly calculated theoretical stellar isochrone of age 2.5 Gyr, which we take to be the age of the cluster. Both the depth gained in the photometry and the increased projected area of the CFH12K Mosaic CCD allow for detailed star counts in concentric annuli out to large angular radii. These indicate a much larger cluster extent (R = 95 ± 10), by a factor of ~2 over some previous estimates. Incompleteness tests confirm a slightly negatively sloped luminosity function extending to faint (V ~ 23) magnitudes which is indicative of a dynamically evolved cluster. Further luminosity function and mass segregation tests indicate that low-mass objects (M ≤ 0.65 M⊙) predominate in the outer regions of the cluster, 35 ≤ R ≤ 95. The estimation of the number of white dwarfs in NGC 6819, based on stellar evolution models, white dwarf cooling timescales, and conservation of star number arguments applied to the red giant stars of the cluster are in good agreement with the observed number. For those white dwarf candidates which pass both a statistical subtraction that removes background galaxies and field stars and a high star/galaxy confidence by using image classification, we show comparisons with white dwarf isochrones and cooling models which suggest the need for spectroscopy to confirm the white dwarf nature of the brighter objects. This is entirely feasible for all objects, before a statistical subtraction cut, with the current generation of 8 m–class telescopes and multiobject spectrometers.

109 citations

Journal ArticleDOI
TL;DR: In this article, the first results of a deep WFPC2 photometric survey of the loose galactic globular cluster NGC 288 were presented, where the fraction of binary systems is estimated from the color distribution of objects near the Main Sequence (MS) with a method analogous to that introduced by Rubenstein & Bailyn(1997).
Abstract: We present the first results of a deep WFPC2 photometric survey of the loose galactic globular cluster NGC 288. The fraction of binary systems is estimated from the color distribution of objects near the Main Sequence (MS) with a method analogous to that introduced by Rubenstein & Bailyn(1997). We have unequivocally detected a significant population of binary systems which has a radial distribution that has been significantly influenced by mass segregation. In the inner region of the cluster (r 1 r_h), f_b must be less than 0.10, and the most likely value is 0.0, independently of the adopted F(q). The detected population of binaries is dominated by primordial systems. The specific frequency of Blue Straggler Stars (BSS) is exceptionally high, suggesting that the BSS production mechanism via binary evolution can be very efficient. A large population of BSS is possible even in low density environments if a sufficient reservoir of primordial binaries is available. The observed distribution of BSS in the Color Magnitude Diagram is not compatible with a rate of BSS production which has been constant in time, if it is assumed that all the BSS are formed by the merging of two stars.

109 citations

Journal ArticleDOI
TL;DR: In this paper, photometric, structural and dynamical evolution-related parameters of 11 nearby open clus- ters with ages in the range 70Myr to 7Gyr and masses of approximately 400M to 5300M were derived from the background-subtracted radial density profiles.
Abstract: Received -; accepted - Abstract. We derive photometric, structural and dynamical evolution-related parameters of 11 nearby open clus- ters with ages in the range 70Myr to 7Gyr and masses in the range � 400M⊙ to � 5300M⊙. The clusters are homogeneously analysed by means of J, H and KS 2MASS photometry, which provides spatial coverage wide enough to properly take into account the contamination of the cluster field by Galaxy stars. Structural parameters such as core and limiting radii are derived from the background-subtracted radial density profiles. Luminosity and mass functions (MFs) are built for stars later than the turnoff and brighter than the 2MASS PSC 99.9% completeness limit. The total mass locked up in stars in the core and the whole cluster, as well as the correspond- ing mass densities, are calculated by taking into account the observed stars (evolved and main sequence) and extrapolating the MFs down to the H-burning mass limit, 0.08M⊙. We illustrate the methods by analysing for the first time in the near-infrared the populous open clusters NGC2477 and NGC2516. For NGC2477 we derive an age of 1.1±0.1Gyr, distance from the Sun d⊙ = 1.2±0.1kpc, core radius Rcore = 1.4±0.1pc, limiting radius Rlim = 11.6 ± 0.7pc and total mass mtot � (5.3 ± 1.6) × 10 3 M⊙. Large-scale mass segregation in NGC2477 is reflected in the significant variation of the MF slopes in different spatial regions of the cluster, and in the large number-density of giant stars in the core with respect to the cluster as a whole. For NGC2516 we derive an age of 160 ± 10Myr, d⊙ = 0.44 ± 0.02 kpc, Rcore = 0.6 ± 0.1pc, Rlim = 6.2 ± 0.2pc and mtot � (1.3 ± 0.2) × 10 3 M⊙. Mass-segregation in NGC2516 shows up in the MFs. Six of the 11 clusters present a slope break in the MF occurring at essentially the same mass as that found for the field stars in Kroupa's universal IMF. The MF break is not associated to cluster mass, at least in the clusters in this paper. In two clusters the low-mass end of the MF occurs above the MF break. However, in three clusters the MF break does not occur, at least for the mass range m � 0.7M⊙. One possibility is dynamical evolution affecting the MF slope distribution. We also search for relations of structural and evolutionary parameters with age and Galactocentric distance. The main results for the present sample are: (i) cluster size correlates both with age and Galactocentric distance; (ii) because of size and mass scaling, core and limiting radii, and core and overall mass correlate; (iii) massive (m � 1000M⊙) and less-massive clusters follow separate correlation paths on the plane core radius and overall mass; (iv) MF slopes of massive clusters are restricted to a narrow range, while those of the less-massive ones distribute over a wider range. Core and overall MF flattening is related to the ratio (�) of age to relaxation time. For large values ofthe effects of large-scale mass segregation and low-mass stars evaporation can be observed in the MFs. In this sense, � appears to characterize the evolutionary state of the clusters. We conclude that appreciable slope flattenings in the overall MFs of the less-massive clusters take � 6 times longer to occur than in the core, while in the massive clusters they take a time � 13 times longer. We investigate cluster parameters equivalent to those determining the fundamental plane of ellipticals. These parameters are: overall mass, projected mass density and core radius. We conclude that in the present sample there is evidence of a fundamental plane. Larger samples are necessary to pin down this issue.

108 citations

Journal ArticleDOI
TL;DR: In this paper, the galaxy stellar mass function (MF) and its evolution in clusters from z~0.8 to the current epoch, based on the WIde-field Nearby Galaxy-cluster Survey (WINGS) (0.04 10^11 M' does not evolve, but below M*~10^10.8 M' the MF at high redshift is flat, while in the Local Universe it flattens out at lower masses.
Abstract: We present the galaxy stellar mass function (MF) and its evolution in clusters from z~0.8 to the current epoch, based on the WIde-field Nearby Galaxy-cluster Survey (WINGS) (0.04 10^11 M' does not evolve, but below M*~10^10.8 M' the MF at high redshift is flat, while in the Local Universe it flattens out at lower masses. The population of M* = 10^10.2 - 10^10.8 M' galaxies must have grown significantly between z=0.8 and z=0. We analyze the MF of different morphological types (ellipticals, S0s and late-types), and find that also each of them evolves with redshift. All types have proportionally more massive galaxies at high- than at low-z, and the strongest evolution occurs among S0 galaxies. Examining the morphology-mass relation (the way the proportion of galaxies of different morphological types changes with galaxy mass), we find it strongly depends on redshift. At both redshifts, ~40% of the stellar mass is in elliptical galaxies. Another ~43% of the mass is in S0 galaxies in local clusters, while it is in spirals in distant clusters. To explain the observed trends, we discuss the importance of those mechanisms that could shape the MF. We conclude that mass growth due to star formation plays a crucial role in driving the evolution. It has to be accompanied by infall of galaxies onto clusters, and the mass distribution of infalling galaxies might be different from that of cluster galaxies. However, comparing with high-z field samples, we do not find conclusive evidence for such an environmental mass segregation. Our results suggest that star formation and infall change directly the MF of late-type galaxies in clusters and, indirectly, that of early-type galaxies through subsequent morphological transformations.

107 citations

Journal ArticleDOI
TL;DR: In this article, a photometric survey of 42 open clusters was conducted to derive structural and astrophysical parameters for open clusters, including radial density profiles and core radii, and the ages, reddenings, and distances were obtained from the solar metallicity isochrone fitting.
Abstract: Aims. We present results of a photometric survey whose aim was to derive structural and astrophysical parameters for 42 open clusters. While our sample is definitively not representative of the total open cluster sample in the Galaxy, it does cover a wide range of cluster parameters and is uniform enough to allow for simple statistical considerations. Methods. BV wide-field CCD photometry was obtained for open clusters for which photometric, structural, and dynamical evolution parameters were determined. The limiting and core radii were determined by analyzing radial density profiles. The ages, reddenings, and distances were obtained from the solar metallicity isochrone fitting. The mass function was used to study the dynamical state of the systems, mass segregation effect and to estimate the total mass and number of cluster members. Results. This study reports on the first determination of basic parameters for 11 out of 42 observed open clusters. The angular sizes for the majority of the observed clusters appear to be several times larger than the catalogue data indicate. The core and limiting cluster radii are correlated and the latter parameter is 3.2 times larger on average. The limiting radius increases with the cluster's mass, and both the limiting and core radii decrease in the course of dynamical evolution. For dynamically not advanced clusters, the mass function slope is similar to the universal IMF slope. For more evolved systems, the effect of evaporation of low-mass members is clearly visible. The initial mass segregation is present in all the observed young clusters, whereas the dynamical mass segregation appears in clusters older than about $\log({age})$ = 8. Low-mass stars are deficient in the cores of clusters older than $\log({age})$ = 8.5 and not younger than one relaxation time.

106 citations


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Performance
Metrics
No. of papers in the topic in previous years
YearPapers
202336
202225
202133
202047
201943
201822