166 research outputs found
The Future of Extragalactic Research
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
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
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 Light Curve of S Andromedae
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
Globular Clusters in Dwarf Galaxies
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 is found to differ dramatically from that for globular clusters
surrounding giant host galaxies with . The luminosity distribution
of globular clusters in giant galaxies peaks at , whereas that
for dwarfs is found to increases monotonically down to the completeness limit
of the cluster data at . 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 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 Formation and Evolution of Massive Star Clusters: Historical Overview
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
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