15,207 research outputs found
The Flattening of Globular Clusters
In the three nearest luminous galaxies, the Milky Way System, the Andromeda
Galaxy and NGC 5128 the brightest globular clusters are rounder than the
faintest ones. On the other hand (contrary to some previous results) the
flattening of individual LMC clusters is found to be independent of their
luminosities. This suggests the possibility that the relationship between the
flattening and luminosity of clusters might depend on host galaxy luminosity.
No significant differences are found between the intrinsic flattening
distributions of Galactic old halo, Galactic young halo and Galactic bulge/disk
clusters. Such a dependence might perhaps have been expected if tidal forces
(which are largest at small Galactocentric distances) removed angular momentum
from globular clusters. The preliminary conclusion by Norris that clusters with
blue horizontal branches are more flattened than red HB clusters is not
confirmed by the larger data base that is now available. In other words there
is no evidence for the puzzling claimed correlation between the flattening and
the horizontal branch morphology of Galactic globular clusters.Comment: 20 pages text + tables; 5 postscript figures. Astronomical Journal,
in pres
Classifications of the Host Galaxies of Supernovae, Set II
Classifications on the DDO system are given for an additional 231 host
galaxies of supernovae that have been discovered during the course of the Lick
Observatory Supernova Search with the Katzman Automatic Imaging Telescope
(KAIT). This brings the total number of hosts of supernovae discovered (or
independently rediscovered) by KAIT, which have so far been classified on a
homogeneous system, to 408. The probability that SNe Ia and SNe II have a
different distribution of host galaxy Hubble types is found to be 99.7%. A
significant difference is also found between the distributions of the host
galaxies of SNe Ia and of SNe Ibc (defined here to include SNe Ib, Ib/c, and
Ic). However, no significant difference is detected between the frequency
distributions of the host galaxies of SNe II and SNe IIn. This suggests that
SNe IIn are generally not SNe Ia embedded in circumstellar material that are
masquerading as SNe II. Furthermore, no significant difference is found between
the distribution of the Hubble types of the hosts of SNe Ibc and of SNe II.
Additionally, SNe II-P and SNe II-L are found to occur among similar stellar
populations. The ratio of the number of SNe Ia-pec to normal SNe Ia appears to
be higher in early-type galaxies than it is in galaxies of later morphological
types. This suggests that the ancestors of SNe Ia-pec may differ systematically
in age or composition from the progenitors of normal SNe Ia. Unexpectedly, five
SNe of Types Ib/c, II, and IIn (all of which are thought to have massive
progenitors) are found in host galaxies that are nominally classified as types
E and S0. However, in each case the galaxy classification is uncertain, or
newly inspected images show evidence suggesting a later classification
(abridged) ...Comment: Accepted for publishing in PAS
The Mass of the Centaurus A Group of Galaxies
The mass M, and the radius R_h, of the Centaurus A group are estimated from
the positions and radial velocities of 30 probable cluster members. For an
assumed distance of 3.9 Mpc it is found that R_h \sim 640 kpc. The velocity
dispersion in the Cen A group is 114 \pm 21 km/s. From this value, and R_h =
640 kpc, the virial theorem yields a total mass of 1.4 \times 10^{13} M_{\sun}
for the Cen A group. The projected mass method gives a mass of 1.8 \times
10^{13} M_{\sun}. These values suggest that the Cen A group is about seven
times as massive as the Local Group. The Cen A mass-to-light ratio is found to
be M/L_B = 155-200 in solar units. The cluster has a zero-velocity radius R_0 =
2.3 Mpc.Comment: 8 pages, 1 figure, in LaTeX format; to appear in the Astronomical
Journal in January 200
Are the Luminosities of RR Lyrae Stars Affected by Second Parameter Effects?
There is a serious discrepancy between the distance to the LMC derived from
the Cepheid Period-Luminosity relation and that obtained by using the Galactic
calibration for the luminosity of RR Lyrae stars. It is suggested that this
problem might be due to the fact that second parameter effects make it
inappropriate to apply Galactic calibrations to RR Lyrae variables in the
Magellanic Clouds, i.e. Mv(RR) could depend on both [Fe/H] and on one or more
second parameters.Comment: 10 pages as uuencoded compressed Postscript. Also available at
http://www.dao.nrc.ca/DAO/SCIENCE/science.htm
What are S0 (0) Galaxies?
Among early-type galaxies with almost circular isophotes E0 and E1 galaxies
are, at 99.3% significance, more luminous than face-on objects classified as S0
(0) and S(0) (1). This result supports the view that rotation and "diskiness"
are more important in the outer regions of faint-early type galaxies than they
are for more luminous galaxies of very early morphological type.Comment: 7 pages. 0 figures. Astrophysical Jounral Letters in pres
Classifications of the Host Galaxies of Supernovae
Classifications on the DDO system are given for the host galaxies of 177
supernovae (SNe) that have been discovered since 1997 during the course of the
Lick Observatory Supernova Search with the Katzman Automatic Imaging Telescope.
Whereas SNe Ia occur in all galaxy types, it is found, at a high level of
statistical confidence, that SNe Ib, Ic, and II are strongly concentrated in
late-type galaxies. However, attention is drawn to a possible exception
provided by SN 2001I. This SN IIn occurred in the E2 galaxy UGC 2836, which was
not expected to harbor a massive young supernova progenitor.Comment: Accepted to be published in PAS
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
Hypersurface homogeneous Killing spinor space-times
I present a complete list of hypersurface homogeneous space-times admitting a
non-null valence two Killing spinor, including a new class admitting only
exceptional Killing tensors. A connection is established with the
classification of locally rotationally symmetric or boost symmetric
space-times.Comment: 16 page
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
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