Mass segregation

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

Mass segregation of different populations inside the cluster NGC6101

Abstract: We have used ESO telescopes at La Silla and the Hubble Space Telescope (HST) in order to obtain accurate B,V,I CCD photometry for the stars located within 200" (~= 2 half-mass radii, r_h = 1.71') from the center of the cluster NGC 6101. Color-Magnitude Diagrams extending from the red-giant tip to about 5 magnitudes below the main-sequence turnoff MSTO (V = 20.05 +- 0.05) have been constructed. The following results have been obtained from the analysis of the CMDs: a) The overall morphology of the main branches confirms previous results from the literature, in particular the existence of a sizeable population of 73 "blue stragglers", which had been already partly detected (27).They are considerably more concentrated than either the subgiant branch or the main sequence stars, and have the same spatial distribution as the horizontal branch stars (84% prob. from K-S test). An hypothesis on the possible BSS progeny is also presented. b) The HB is narrow and the bulk of stars is blue, as expected for a typical metal-poor globular cluster. c) The derived magnitudes for the HB and the MSTO, $V(ZAHB) = 16.59+-0.10, V(TO) = 20.05+-0.05, coupled with the values E(B-V) = 0.1, [Fe/H] = -1.80, Y = 0.23 yield a distance modulus (m-M)_V = 16.23 and an age similar to other ``old'' metal-poor globular clusters. In particular, from the comparison with theoretical isochrones, we derive for this cluster an age of 13 Gyrs. d) By using the large statistical sample of Red Giant Branch (RGB) stars, we detected with high accuracy the position of the bump in the RGB luminosity function. This observational feature has been compared with theoretical prescriptions, yielding a good agreement within the current theoretical and observational uncertainties.

Star cluster formation from turbulent clumps. II. Gradual star cluster formation

Abstract: We investigate the dynamical evolution of star clusters during their formation, assuming that they are born from a turbulent starless clump of a given mass that is embedded within a parent self-gravitating molecular cloud characterized by a particular mass surface density. In contrast to the standard practice of most N-body studies, we do not assume that all stars are formed at once. Rather, we explore the effects of different star formation rates on the global structure and evolution of young embedded star clusters, also considering various primordial binary fractions and mass segregation levels. Our fiducial clumps studied in this paper have initial masses of M cl = 3000M ⊙ , are embedded in ambient cloud environments of σ cloud = 0.1 and 1 g cm -2 , and gradually form stars with an overall efficiency of 50 per cent until the gas is exhausted. We investigate star formation efficiencies per free-fall time in the range ϵ ff = 0.01-1, and also compare to the instantaneous case (ϵ ff = α) of Paper I. We show that most of the interesting dynamical processes that determine the future of the cluster, happen during the early formation phase. In particular, the ejected stellar population is sensitive to the duration of star cluster formation: for example, clusters with longer formation times produce more runaway stars, since these clusters remain in a dense state for longer, thus favouring occurrence of dynamical ejections. We also show that the presence of radial age gradients in star clusters depends sensitively on the star formation efficiency per free-fall time, with observed values being matched best by our slowest forming clusters with ϵ ff ≲0.03.

Disintegration of the Aged Open Cluster Berkeley 17

Abstract: We present the analysis of the morphological shape of Berkeley 17, the oldest known open cluster (~10 Gyr), using the probabilistic star counting of Pan-STARRS point sources, and confirm its core-tail shape, plus an antitail, previously detected with the 2MASS data. The stellar population, as diagnosed by the color–magnitude diagram and theoretical isochrones, shows many massive members in the clusters core, whereas there is a paucity of such members in both of the tails. This manifests mass segregation in this aged star cluster with the low-mass members being stripped away from the system. It has been claimed that Berkeley 17 is associated with an excessive number of blue straggler candidates. A comparison of nearby reference fields indicates that about half of these may be field contamination.

Radial Color Gradient and Main-Sequence Mass Segregation in M30 (NGC 7099)* **

Abstract: It has long been known that the post–core-collapse globular cluster M30 (NGC 7099) has a bluer-inward color gradient, and recent work suggests that the central deficiency of bright red giant stars does not fully account for this gradient. This study uses Hubble Space Telescope Wide Field Planetary Camera 2 images in the F439W and F555W bands, along with ground-based CCD images with a wider field of view for normalization of the noncluster background contribution, and finds Δ(B-V) ~ 0.3 mag for the overall cluster starlight over the range 2'' to 1' in radius. The slope of the color profile in this radial range is Δ(B-V)/Δ log r = +0.20 ± 0.07 mag dex-1, where the quoted uncertainty accounts for Poisson fluctuations in the small number of bright evolved stars that dominate the cluster light. We explore various algorithms for artificially redistributing the light of bright red giants and horizontal-branch stars uniformly across the cluster. The traditional method of redistribution in proportion to the cluster brightness profile is shown to be inaccurate. There is no significant residual color gradient in M30 after proper uniform redistribution of all bright evolved stars; thus, the color gradient in M30's central region appears to be caused entirely by post–main-sequence stars. Two classes of plausible dynamical models, Fokker-Planck and multimass King models, are combined with theoretical stellar isochrones from Bergbusch V this is consistent with M30's residual color gradient within measurement error. The observed fraction of evolved-star light in the B and V bands agrees with the corresponding model predictions at small radii but drops below it for r 20''.

A Search for Environmental Influence on Stellar Mass

Abstract: The positions and local projected densities of the protostellar continuum sources in Ophiuchus and Serpens are investigated as a function of their masses in order to search for possible environmental effects during star formation. There is a slight trend toward mass segregation for the 850 μm sources found by Johnstone and coworkers in Ophiuchus, but there is no obvious mass segregation for the 1.3 mm sources in Ophiuchus or Serpens. There is also no systematic change in the local projected source density with source mass, as might be expected if clump collisions or gas clearing are involved.