Showing papers on "Mass segregation published in 1988"

A study of the spatial stellar mass distribution in some young open clusters

Abstract: The stellar spatial distribution as a function of mass is studied in 11 young open clusters and the presence of mass segregation is observed in seven of these. The possibility of two cluster centres is indicated for NGC 2264. Except in Tr 1, the conventional relaxation and energy equipartition times are larger than the cluster ages which may indicate that the observed mass segregation is due to the star formation processes. However, the possibility of dynamical processes being responsible for the effect of mass segregation in some of these clusters cannot be completely ruled out. Present analysis suggests that observed mass segregation in open clusters older than some million years might be due to a combination of both initial star formation conditions and dynamical evolutionary processes, but in younger ones only initial star formation conditions can be responsible.

Comparative Properties of Virgo Cluster Dwarf Irregulars and Spirals

Abstract: The optical and neutral hydrogen data for all spiral and late-type dwarf irregular galaxies in the Virgo Cluster catalog are analyzed. In particular, the continuity of optical properties, hydrogen masses, and dynamical properties are examined as functions of morphology and luminosity from the largest spirals through the faintest dwarfs (omitting blue compact dwarf galaxies); the effects of environment on H I content; mass segregation; and the Tully-Fisher relations. The spiral plus dwarf sample forms a continuous but nonhomologous sequence. Indicative dynamical mass-to-light ratios are relatively constant throughout; hydrogen mass-to-light ratios show only a slight increase with decreasing luminosity. The Tully-Fisher relations extend with continuous slope from spirals through dwarfs. The dwarfs show some evidence of ram-pressure stripping by the intracluster medium, but as a group do not seem to be stripped more heavily than spirals. There is no evidence of mass segregation even for the very low mass dwarfs versus giant spirals.

Mass segregation and formation of X-ray sources in globular clusters

Abstract: Les distributions radiales de densite de deux amas globulaires differents (ω Cen et 47 Tuc) sont comparees pour tester des processus de capture d'une etoile (naine blanche ou a neutrons) par une autre (geante ou de la sequence principale). La probabilite de formation d'etoiles binaires RX de faible masse est ainsi determinee; de meme pour les variables cataclysmiques

Field star contamination in open star cluster NGC 2301.

Abstract: Photographic photometry of about 900 stars down to V = 17 mag has been carried out in the region of the open cluster NGC 2301. The cluster region seems to be severely contaminated by field stars. Statistical criteria yield only 96 ± 17 cluster members. Stars fainter than ~ 15 mag are found to be absent among cluster members. Star counts indicate a diameter of ~ 20 arcmin. The data suggest mass segregation in the cluster.

Evolution of Globular Clusters Including a Degenerate Component

Abstract: Low mass X-ray sources observed in many globular clusters are usually interpreted as compact binaries with degenerate components (e.g., Hertz and Grindlay 1983). Degenerate stars can exist in globular clusters if the IMF contains a sufficiently large number of high mass stars. Since the main-sequence lifetime is a very steep function of stellar mass, most of degenerate stars can be regarded as primordial. If the typical mass of degenerate stars is higher than that of main-sequence stars, mass segregation makes the core crowded with degenerate stars. Tidally captured binaries between degenerates and main-sequence stars can abundantly form as the core density becomes very high.

Evidence for Mass Segregation in NGC 5466

Abstract: Forty-eight blue straggler stars have been discovered in NGC 5466, the only Galactic globular cluster known to contain an anomalous Cepheid of the sort found in dwarf galaxies The stars were identified in color-magnitude diagrams constructed from photometry of deep photographic plates taken with the Canada-France-Hawaii 36 m telescope (calibrated with new UBV photoelectric photometry), and from point spread function photometry of CCD frames taken with the Palomar 5 m telescope The stars typically have magnitudes ∼ 19 m 1 and colors ∼ 0 m 2 Forty-two of the 48 stars are situated inside of R=25 arcmin (see Fig1), the projected radius containing half the cluster luminosity, and only six stars are found between 25 and 9 arcmin A one-sided, two-sample Kolmogorov-Smirnov test (using the CCD data) establishes at the 98% significance level that the blue stragglers are more centrally concentrated than the subgiant stars of the same magnitude By fitting multi-component King models to the projected radial distributions (Fig2), the mean mass of the blue stragglers is shown to be ∼15 to two times larger than the masses of the stars that contributed the light from which the core and tidal radii were derived (ie M(Blue Str)=13±03 M⊙) Because the central relaxation time for NGC 5466 is much less than the cluster age, the different radial distributions are attributed to mass segregation A similar mass segregation is also observed in the globular cluster NGC 5053, where Nemec and Cohen (1986, in preparation) have recently identified ∼30 blue stragglers The low stellar aensity and small escape velocity of NGC 5466 make a recent epoch of star formation (during which the blue stragglers might have formed as massive single stars) seem unlikely Instead, the blue stragglers probably are either close binary systems that have transferred mass, or are coalesced stars The very low frequency of stellar collisions expected in the center of NGC 5466 suggests that the blue stragglers are primordial binary systems The simultaneous presence in NGC 5466 of the blue stragglers and the anomalous Cepheid V19, and their relative numbers, supports the hypothesis that there is an evolutionary connection between the two types of stars By fitting theoretical isochrones to the photographic c-m diagram, NGC 5466 is estimated to have an age of 18±3 Gyr

Project for the Photometry of Clusters of Galaxies

Abstract: The main methods of investigating the structures of clusters of galaxies up to the present time are based on simple galaxy counts. N-body simulations of ensembles of point masses were used to explain these observations. But clusters of galaxies are not ensembles of point masses. The large spectrum of masses of galaxies in clusters as well as the spatial extension of the galaxies will influence the evolution of clusters in a dominant manner. Up to now there exist only very few investigations of the distribution of masses in clusters. They are restricted to the problem of mass segregation in some clusters, as Coma or Centaurus. Such discussions are based upon photometry of galaxies in clusters. Today we consider photometry on photographic plates as the only economic method for the investigation of luminosities of a large number of galaxies. But there is an important disadvantage of this method. It concerns its insufficient accuracy. There are the following main reasons for photometric errors: 1. Scale errors due to bad calibration of sensitometers and to light diffusion. 2. Instabilities of the measuring device. 3. Inhomogeneities in the photographic emulsion.