3,517 research outputs found
The Shape of Dark Matter Halos
Techniques for inferring the radial and geometric form of dark matter halos
and the results they have produced to date are reviewed. Dark halos appear to
extend to at least ~50 kpc with total enclosed masses that rise linearly with
radius R. Whether this behavior can be extrapolated to distances as large as
200 kpc and beyond is controversial; results at this radius are
model-dependent. Observationally, the geometrical form of the dark halo can be
characterized by the equatorial axis ratio b/a (ovalness) and
vertical-to-equatorial axis ratio c/a (flattening) of the total density.
Different techniques consistently yield b/a > 0.7 (and thus b/a > 0.9 for the
potential) at R~20 kpc, with more axisymmetric values, b/a >~ 0.8, being more
likely. Results are less consistent for the vertical flattening, perhaps due to
the difference in the spatial regions probed by different techniques or
inappropriate assumptions. Techniques that probe furthest from the stellar
plane z~15 kpc consistently implicate substantially flattened c/a = 0.5 +/- 0.2
dark halos. These axis ratios are in acceptable agreement with expectations
from N-body simulations of cold dark matter mixed with ~10% dissipational gas.Comment: Invited Review to appear in Galaxy Dynamics, 1999, eds. D. Merritt,
J.A. Sellwood and M. Valluri, ASP, LaTex using paspconf.sty, 3 figures in 5
postscript file
Planetary Microlensing: Present Status and Long-term Goals
Massive gravitational microlensing programs were begun about a decade ago as
a means to search for compact baryonic dark matter in the Galaxy, but before
the first events were detected the technique was also proposed as a means of
detecting extra-solar planets in our Galaxy. Current microlensing planet
searches, which have been underway for four years, are sensitive to jovian-mass
planets orbiting a few to several AU from their parent Galactic stars. Within
two years, sufficient data should be in hand to characterize or meaningfully
constrain the frequency of massive planets in this range of parameter space,
nicely complementing information about planets at smaller orbital radii now
being provided by radial velocity searches. In principle, the technique could
be pushed to smaller planetary masses, but only if a larger number of faint
microlensed sources can be monitored with higher precision and temporal
sampling. The VST on Paranal, with spectroscopic follow-up with the VLT, may be
the ideal instrument for such an ambitious program.Comment: Invited Review at VLT Opening Symposium, Antofagasta, Chile, March
1999. To appear in the Springer-Verlag series ``ESO Astrophysics Symposia'
Another Flattened Dark Halo: Plar Ring Galaxy A0136-0801
Knowledge of the shape of dark matter halos is critical to our understanding
of galaxy formation, dynamics, and of the nature of dark matter itself. Polar
ring galaxies (PRGs) --- early-type galaxies defined by their outer rings of
gas, dust and stars on orbits nearly perpendicular to those of the central host
--- provide a rare probe of the vertical-to-radial axis ratio of dark halos. We present a Fabry-Perot velocity field for the H
gas in the kinematically-confirmed PRG \gal. By comparing ring orbits evolved
in a generalized mass model to the observed ring velocity field and morphology
of \gal, we conclude that and rule out a spherical geometry.Comment: uuencoded gz-compressed file with figures include
The Distribution of Dark Mass in Galaxies: Techniques, Puzzles, and Implications for Lensing
Gravitational lensing is one of a number of methods used to probe the
distribution of dark mass in the Universe. On galactic scales, complementary
techniques include the use of stellar kinematics, kinematics and morphology of
the neutral gas layer, kinematics of satellites, and morphology and temperature
profile of X-ray halos. These methods are compared, with emphasis on their
relative strengths and weaknesses in constraining the distribution and extent
of dark matter in the Milky Way and other galaxies. It is concluded that (1)
the extent of dark halos remains ill-constrained, (2) halos need not be
isothermal, and (3) the dark mass is probably quite flattened.Comment: Invited Review at IAU Symposium 173, "Gravitational Lensing,"
Melbourne, July 1995, eds. C. Kochanek and J. Hewitt. 10 pages, 1 Postscript
Figure. A few typos have been corrected and a few references adde
SuperLupus: A Deep, Long Duration Transit Survey
SuperLupus is a deep transit survey monitoring a Galactic Plane field in the
Southern hemisphere. The project is building on the successful Lupus Survey,
and will double the number of images of the field from 1700 to 3400, making it
one of the longest duration deep transit surveys. The immediate motivation for
this expansion is to search for longer period transiting planets (5-8 days) and
smaller radii planets. It will also provide near complete recovery for the
shorter period planets (1-3 days). In March, April, and May 2008 we obtained
the new images and work is currently in progress reducing these new data.Comment: 3 pages, 2 figures, to appear in the Proceedings of IAU Symposium
253, 2008: Transiting Planet
A review of data visualization: opportunities in manufacturing sequence management.
Data visualization now benefits from developments in technologies that offer innovative ways of presenting complex data. Potentially these have widespread application in communicating the complex information domains typical of manufacturing sequence management environments for global enterprises. In this paper the authors review the visualization functionalities, techniques and applications reported in literature, map these to manufacturing sequence information presentation requirements and identify the opportunities available and likely development paths. Current leading-edge practice in dynamic updating and communication with suppliers is not being exploited in manufacturing sequence management; it could provide significant benefits to manufacturing business. In the context of global manufacturing operations and broad-based user communities with differing needs served by common data sets, tool functionality is generally ahead of user application
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