Mass segregation

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

Depletion of dark matter within globular clusters

Abstract: Gravitationally bound group of stars which are identified as globular clusters are known to have a small amount of dark matter. Assuming that globular clusters are formed within dark matter halos, they must have lost significant amount of dark matter. Observations of globular clusters reported flattening velocity dispersion on the outskirt clusters. This could be a sign of existence of dark matter. Theoretically, dynamical processes such as dynamical friction and mass segregation and tidal stripping could be responsible for the depletion of dark matter from the cluster center. Numerical simulations are conducted to follow the evolution of the models of globular clusters composed out of stars and dark matter particles. The results show that the dark matter is depleted from the center of globular clusters due to dynamical friction and mass segregation of stars. An external tidal field from a Milky Way like galaxy effects to deplete the dark matter in the outer part of the clusters. However, within the Hubble time, about 80 % of dark matter's initial values still remain in the outer part of clusters. This might explain the existence of significant amount of dark matter in the outer part of observed clusters.

Mass Segregation in Star Clusters in the LMC HST/WFPC2 Observations

Abstract: The Large Magellanic Cloud (LMC) provides a unique laboratory for the study of the star‐formation process, because of its large sample of young stellar systems, such as stellar associations (e.g. Hodge) and young compact star clusters (e.g. van den Bergh). Mass segregation nowadays is a well known phenomenon, which manifests itself as a strong concentration of the heaviest stars towards the centre of the cluster, and recent investigations have shown that even young star clusters in the Magellanic Clouds (MCs) exhibit this phenomenon (e.g. Kontizas et al.; Fischer et al.; Kontizas et al.; Santiago et al.; de Grijs et al.; Sirianni et al.; Gouliermis et al.). A large set of young and old clusters observed with HST has been selected for this study. Preliminary results are given for NGC 1916 an old cluster with age 2×108yr, in which mass segregation is detected from its Mass Function. The continuation of this study will determine in a definite manner which is the origin for this phenomenon (primordial or dyna...

A Multi-Wavelength Study of the Segue 3 Cluster

Abstract: We present new SDSS and Washington photometry of the young, outer-halo stellar system, Segue 3. Combined with archival VI-observations, our most consistent results yield: $Z=0.006$, $\log(Age)=9.42$, $(m-M)_0=17.35$, $E(B-V)=0.09$, with a high binary fraction of $0.39\pm 0.05$, using the Padova models. We confirm that mass segregation has occurred, supporting the hypothesis that this cluster is being tidally disrupted. A 3-parameter King model yields a cluster radius of $r_{cl}=0.017^\circ$, a core radius of $r_{c}=0.003^\circ$, and a tidal radius of $r_t=0.04^\circ \pm 0.02^\circ$. A comparison of Padova and Dartmouth model-grids indicates that the cluster is not significantly $\alpha$-enhanced, with a mean [Fe/H]$=-0.55^{+0.15}_{-0.12}$ dex, and a population age of only $2.6\pm 0.4$ Gyr. We rule out a statistically-significant age spread at the main sequence turnoff because of a narrow subgiant branch, and discuss the role of stellar rotation and cluster age, using Dartmouth and Geneva models: approximately 70% of the Seg 3 stars at or below the main sequence turnoff have enhanced rotation. Our results for Segue 3 indicate that it is younger and more metal-rich than all previous studies have reported to-date. From colors involving Washington-C and SDSS-u filters, we identify several giants and a possible blue-straggler for future follow-up spectroscopic studies, and we produce spectral energy distributions of previously known members and potential Segue 3 sources with Washington ($CT_1$), Sloan (ugri), and VI-filters. Segue 3 shares the characteristics of unusual stellar systems which have likely been stripped from external dwarf galaxies as they are being accreted by the Milky Way, or that have been formed during such an event. Its youth, metallicity, and location are all inconsistent with Segue 3 being a cluster native to the Milky Way.

The tidal tails of NGC 2298

Abstract: We present an implementation of the matched-filter technique to detect tidal tails of globular clusters. The method was tested using SDSS data for the globular cluster Palomar 5 revealing its well known tidal tails. We also ran a simulation of a globular cluster with a tidal tail where we successfully recover the tails for a cluster at the same position and with the same characteristics of NGC 2298. Based on the simulation we estimate that the matched-filter increases the contrast of the tail relative to the background of stars by a factor of 2.5 for the case of NGC 2298. We also present the photometry of the globular cluster NGC 2298 using the MOSAIC2 camera installed on the CTIO 4m telescope. The photometry covers ~ 3deg2 reaching V ~ 23. A fit of a King profile to the radial density profile of NGC 2298 shows that this cluster has a tidal radius of 15.91' \pm 1.07' which is twice as in the literature. The application of the matched-filter to NGC 2298 reveals several extra-tidal structures, including a leading and trailing tail. We also find that NGC 2298 has extra-tidal structures stretching towards and against the Galactic disk, suggesting strong tidal interaction. Finally, we assess how the matched-filter performs when applied to a globular cluster with and without mass segregation taken into account. We find that disregarding the effects of mass segregation may significantly reduce the detection limit of the matched-filter.