Mass segregation

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

A detailed study of the enigmatic cluster M82F

Abstract: We present a detailed study of the stellar cluster M82F, using multiband high-resolution Hubble Space Telescope (HST) imaging and deep ground-based optical slit and integral field spectroscopy. Using the imaging, we create colour maps of the cluster and surrounding region in order to search for substructure. We find a large amount of substructure, which we interpret as the result of differential extinction across the projected face of the cluster. With this interpretation, we are able to construct a spatially resolved extinction map across the cluster which is used to derive the intrinsic flux distribution. Fitting cluster profiles (King and Elson, Fall & Freeman) to the intrinsic images, we find that the cluster is 15-30 per cent larger than previous estimates, and that no strong evidence of mass segregation in this cluster exists. Using the optical spectra, we find that the age of M82F is 60-80 Myr and from its velocity conclude that the cluster is not physically associated with a large H II region that it is projected upon, both in agreement with previous studies. The reconstructed integral field maps show that that majority of the line emission comes from a nearby H II region. The spatial dependence of the line widths (implying the presence of multiple components) measured corresponds to the extinction map derived from photometry, indicating that the gas/dust clouds responsible for the extinction are also partially ionized. Even with the wealth of observations presented here, we do not find a conclusive solution to the problem of the high light-to-mass ratio previously found for this cluster and its possible top-heavy stellar initial mass function.

Analytic study of mass segregation around a massive black hole

Abstract: We analyze the distribution of stars of arbitrary mass function xi(m) around a massive black hole (MBH). Unless xi is strongly dominated by light stars, the steady-state distribution function approaches a power-law in specific energy x=-E/(m*sigma^2)

A highly efficient measure of mass segregation in star clusters

Abstract: Investigations of mass segregation are of vital interest for the understanding of the formation and dynamical evolution of stellar systems on a wide range of spatial scales. Our method is based on the minimum spanning tree (MST) that serves as a geometry-independent measure of concentration. Compared to previous such approaches we obtain a significant refinement by using the geometrical mean as an intermediate-pass. It allows the detection of mass segregation with much higher confidence and for much lower degrees of mass segregation than other approaches. The method shows in particular very clear signatures even when applied to small subsets of the entire population. We confirm with high significance strong mass segregation of the five most massive stars in the Orion Nebula Cluster (ONC). Our method is the most sensitive general measure of mass segregation so far and provides robust results for both data from simulations and observations. As such it is ideally suited for tracking mass segregation in young star clusters and to investigate the long standing paradigm of primordial mass segregation by comparison of simulations and observations.

Structural Parameters of the Messier 87 Globular Clusters

Abstract: We derive structural parameters for ~2000 globular clusters in the giant Virgo elliptical Messier 87 (M87) using extremely deep Hubble Space Telescope images in F606W (V) and F814W (I) taken with the ACS/WFC. The cluster scale sizes (half-light radii rh ) and ellipticities are determined from point-spread-function -convolved King-model profile fitting. We find that the rh distribution closely resembles the inner Milky Way clusters, peaking at rh 2.5 pc and with virtually no clusters more compact than rh 1 pc. The metal-poor clusters have on average an rh 24% larger than the metal-rich ones. The cluster scale size shows a gradual and noticeable increase with galactocentric distance. Clusters are very slightly larger in the bluer waveband V, a possible hint that we may be beginning to see the effects of mass segregation within the clusters. We also derived a color magnitude diagram for the M87 globular cluster system which shows a striking bimodal distribution.

Structure and Mass Segregation in h and χ Persei

Abstract: We use V magnitudes and spectral types to examine the density structure of h and χ Per. We describe an automatic method for deriving spectral types and compare classifications for observations made at two different facilities. With these data, we measure an extinction to the clusters of E(B - V) = 0.52 ± 0.07, consistent with other authors. However, there appears to be a correlation between the spectral types of the stars used and the resulting value of the extinction. We compare extinction values measured by different authors using different numbers of stars and reproduce their values by imposing different cuts in the V magnitude. This variation in color excess versus spectral type suggests that the standard intrinsic colors for the earliest type stars are bluer than the stars in h and χ Per. We measure centers for h and χ Per at α(2000) = 2h18m564 ± 30, δ(2000) = 57°8'25'' ± 23'' and α(2000) = 2h22m43 ± 29, δ(2000) = 57°8'35'' ± 25'', respectively. We fit the density structure of the clusters and find core radii of 1.9 and 2.4 pc, respectively. Integration of the Miller-Scalo initial mass function suggests overall cluster masses of 5500 and 4300 M⊙ and central densities of 27 and 50 M⊙ pc-3, respectively. We find strong evidence of mass segregation in h Per but not in χ Per. Examination of the dynamical timescales, as well as comparisons between the two clusters, suggest that the mass segregation is partly primordial.