165 research outputs found

    The Future of Extragalactic Research

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    It is argued that the astronomy of the twenty-first century will be dominated by computer-based manipulation of huge homogeneous surveys of various types of astronomical objects. Furthermore combination of all observations with large telescopes into a single database will allow data mining on an unprecedented scale.Comment: Millennium Essay to be published in Vol. 119 of the Publications of the Astronomical Society of the Pacific, replaced with a LaTeX version (4 pages

    A Comparison Between the Globular Clusters in NGC 5128 and the Galaxy

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    Some of the properties of the globular clusters in NGC 5128 are compared to those of Galactic globular clusters. Assuming the color- metallicity relations that hold for Galactic globular clusters then the metal-poor clusters in NGC 5128 that have [Fe/H] < -1.80 are significantly fainter than are the more metal-rich globulars in that galaxy. No such metallicity dependent luminosity difference is observed among the globular clusters associated with the Milky Way. Furthermore the NGC 5128 cluster sample contains two objects that, on the basis of their observed colors, appear to be super metal-poor. It is speculated that many of these apparently faint and metal-poor clusters in NGC 5128 are actually objects resembling intermediate-age Galactic open clusters. It is also found that large clusters with FWHM > 10 pc are typically less luminous in NGC 5128 than are their more more compact counterparts. In this respect the NGC 5128 cluster system is similar to the Galactic globular cluster system. Finally, the present data may hint at the possibility that the NGC 5128 cluster system differs from that surrounding the Milky Way, in that the NGC 5128 objects do not seem to exhibit a clear cut gap between the regions of the FWHM vs M_v plane that are occupied by globular clusters and dwarf spheroidal galaxies.Comment: To be published in the Astronomical Journa

    The Extragalactic Distance Scale

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    Cepheid variables are used to derive a Virgo cluster distance of 16.0 +/- 1.5 Mpc. In conjunction with the Coma velocity and the well-established Coma/Virgo distance ratio, this yields a Hubble paprameter Ho = 81 +/- 8 km/s/Mpc. By combining this value with an age of the Universe of at least 16.8 +/- 2.1 Gyr, that is derived from the metal-poor globular cluster M92, one obtains f(Omega,Lambda) > 1.39 +/- 0.22. This value is only marginally consisitent with an Einstein-de Sitter universe with Omega=0 and Lambda=0, which has f=1. An Einstein-de Sitter universe with Omega=1 and Lambda=0, for which f=2/3, appears to be excluded at the 3-sigma level. It is shown that some small recent values of Ho resulted from the intrinsic dispersion in the linear diameters of galaxies, and from the fact that well-observed supernovae of Type Ia exhibit a luminosity range of ~20 at maximum light.Comment: 22 pages, Postscript, no figures. Also available at: http://www.dao.nrc.ca/DAO/SCIENC

    The Formation and Evolution of Massive Star Clusters: Historical Overview

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    Some factors connecting the evolutionary histories of galaxies with the characteristics of their cluster systems are reviewed. Unanswered questions include: How is one to understand the observation that some globular cluster systems have disk kinematics whereas others do not? Why do some galaxies have cluster systems with unimodal metallicity distributions, whereas others have bimodal metallicity distributions? What caused the average ellipticity of individual clusters to differ from galaxy to galaxy?Comment: To be published in ASP Conference Serie

    The Luminosity Distribution of Globular Clusters in Dwarf Galaxies

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    The majority of the globular clusters associated with the Sagittarius dwarf galaxy are faint. In this respect it differs significantly from the globular cluster systems surrounding typical giant galaxies. The observation that most of globular clusters in the outer halo of the Galaxy are also sub-luminous may be understood by assuming that these clusters once also belonged to faint cluster-rich dwarf systems that were subsequently captured and destroyed by the Milky Way System.Comment: Astronomical Journal, in pres

    Globular Clusters in Dwarf Galaxies

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    Data are presently available on the luminosities and half-light radii of 101 globular clusters associated with low-luminosity parent galaxies. The luminosity distribution of globulars embedded in dwarf galaxies having Mv>16M_{v} > -16 is found to differ dramatically from that for globular clusters surrounding giant host galaxies with Mv<16M_{v} < -16. The luminosity distribution of globular clusters in giant galaxies peaks at Mv7.5M_{v} \sim -7.5, whereas that for dwarfs is found to increases monotonically down to the completeness limit of the cluster data at Mv5.0M_{v} \sim -5.0. Unexpectedly, the power law distribution of the luminosities of globular clusters hosted by dwarf galaxies is seen to be much flatter than the that of bright unevolved part of the luminosity distribution of globular clusters associated with giant galaxies. The specific frequency of globular clusters that are fainter than Mv=7.5M_{v} = -7.5 is found to be particularly high in dwarf galaxies. The luminosity distribution of the LMC globular clusters is similar to that in giant galaxies, and differs from those of the globulars in dwarf galaxies. The present data appear to show no strong dependence of globular cluster luminosity on the morphological types of their parent galaxies. No attempt is made to explain the unexpected discovery that the luminosity distribution of globular clusters is critically dependent on parent galaxy luminosity (mass?), but insensitive to the morphological type of their host galaxy.Comment: Figure 6 replaced to be published in the Astronomical Journa

    The Light Curve of S Andromedae

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    Historical observations of S And, in combination with the color versus rate-of-decline relationship for well-observed SN 1991bg-like supernovae, are used to estimate a rate of decline Delta m15 (B) = 2.21 and an intrinsic color at maximum [B(0) - V(0)]o = 1.32 for SN 1885A.Comment: 6 pages, no figures. To appear in the Astronomical Journal Feb 200
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