2,168 research outputs found
The Distribution of Dark Matter in a Ringed Galaxy
Outer rings are located at the greatest distance from the galaxy center of
any feature resonant with a bar. Because of their large scale, their morphology
is sensitive to the distribution of the dark matter in the galaxy. We introduce
here how study of these rings can constrain the mass-to-light ratio of the bar,
and so the percentage of dark matter in the center of these galaxies. We
compare periodic orbits integrated in the ringed galaxy NGC 6782 near the outer
Lindblad resonance to the shape of the outer ring. The non-axisymmetric
component of the potential resulting from the bar is derived from a
near-infrared image of the galaxy. The axisymmetric component is derived
assuming a flat rotation curve. We find that the pinched non-self-intersecting
periodic orbits are more elongated for higher bar mass-to-light ratios and
faster bars. The inferred mass-to-light ratio of the bar depends on the assumed
inclination of the galaxy. With an assumed galaxy inclination of i=41 degrees,
for the orbits to be consistent with the observed ring morphology the
mass-to-light ratio of the bar must be high, greater than 70% of a maximal disk
value. For i=45 degrees, the mass-to-light ratio of the bar is of
the maximal disk value. Since the velocity field of these rings can be used to
constrain the galaxy inclination as well as which periodic orbit is represented
in the ring, further study will yield tighter constraints on the mass-to-light
ratio of the bar. If a near maximal disk value for the bar is required, then
either there would be little dark matter within the bar, or the dark matter
contained in the disk of the galaxy would be non-axisymmetric and would rotate
with the bar.Comment: AAS Latex + jpg Figures, Accepted for publication in Ap
A Neutral Hydrogen Survey of Polar-Ring Galaxies: I. Green Bank Observations of the Northern Sample
We present the results of a neutral hydrogen survey conducted with the Green
Bank 140-foot radio telescope of 47 northern objects in the polar-ring galaxy
atlas of Whitmore \etal\ (1990). We detected 39 of these above our detection
limit of 1.7 \hbox{Jy\CDOT\KMS}; the average measured flux of 21 Jy\CDOT\KMS\
corresponds to an average neutral hydrogen mass of \MSUN
for a Hubble constant of \KMS \ Mpc. For the polar-ring
galaxies in our sample that have also been observed with radio arrays, we find
that the 21\AMIN\ (FWHM) Green Bank beam often includes much more flux than
found by the synthesis instruments for the polar rings alone; some of these
galaxies are known to have gas-rich companions. We compare the neutral hydrogen
content of the sample to the blue luminosity and IRAS fluxes. The \HI-to-blue-
light ratios of the confirmed and probable polar rings are around unity in
solar units, indicating that polar ring galaxies (or their environments) are as
gas-rich as typical irregular galaxies. For their blue luminosity, the
confirmed polar rings are underluminous in the far-infrared, as compared with
the rest of the sample. They are also FIR-underluminous for their \HI\ masses,
which suggests that most of the gas in the ring may be in stable orbits, rather
than flowing inward to trigger star formation in the central galaxy. The more
disordered class of `related objects,' which includes a number of obvious
mergers, is highly luminous in the far-infrared.Comment: 34 pages, LaTeX file, Institute for Advanced Study number AST 93/4
Lupus-TR-3b: A Low-Mass Transiting Hot Jupiter in the Galactic Plane?
We present a strong case for a transiting Hot Jupiter planet identified
during a single-field transit survey towards the Lupus Galactic plane. The
object, Lupus-TR-3b, transits a V=17.4 K1V host star every 3.91405d.
Spectroscopy and stellar colors indicate a host star with effective temperature
5000 +/- 150K, with a stellar mass and radius of 0.87 +/- 0.04M_sun and 0.82
+/- 0.05R_sun, respectively. Limb-darkened transit fitting yields a companion
radius of 0.89 +/- 0.07R_J and an orbital inclination of 88.3 +1.3/-0.8 deg.
Magellan 6.5m MIKE radial velocity measurements reveal a 2.4 sigma K=114 +/-
25m/s sinusoidal variation in phase with the transit ephemeris. The resulting
mass is 0.81 +/- 0.18M_J and density 1.4 +/- 0.4g/cm^3. Y-band PANIC image
deconvolution reveal a V>=21 red neighbor 0.4'' away which, although highly
unlikely, we cannot conclusively rule out as a blended binary with current
data. However, blend simulations show that only the most unusual binary system
can reproduce our observations. This object is very likely a planet, detected
from a highly efficient observational strategy. Lupus-TR-3b constitutes the
faintest ground-based detection to date, and one of the lowest mass Hot
Jupiters known.Comment: 4 pages, 4 figures, accepted for publication in ApJ
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Proceedings of the 3rd International Conference on Manufacturng Research ICMR2005: Advances in Manufacturing Technology and Management
The International Conference on Manufacturing Research (ICMR) is an annual event, normally held in the early part of September. For many years, it was an UK National Conference that had successfully brought academics and industrialists together to share their knowledge and experiences. Now the conference has developed as a major international event with a growing number of international delegates participating to exchange their research findings with UK researchers and practitioners. The next conference (ICMR2005) will be held at Cranfield University, a distinctive postgraduate university focusing on engineering, management and applied science
Searching for Machos (and other Dark Matter Candidates) in a Simulated Galaxy
We conduct gravitational microlensing experiments in a galaxy taken from a
cosmological N-body simulation. Hypothetical observers measure the optical
depth and event rate toward hypothetical LMCs and compare their results with
model predictions. Since we control the accuracy and sophistication of the
model, we can determine how good it has to be for statistical errors to
dominate over systematic ones. Several thousand independent microlensing
experiments are performed. When the ``best-fit'' triaxial model for the mass
distribution of the halo is used, the agreement between the measured and
predicted optical depths is quite good: by and large the discrepancies are
consistent with statistical fluctuations. If, on the other hand, a spherical
model is used, systematic errors dominate. Even with our ``best-fit'' model,
there are a few rare experiments where the deviation between the measured and
predicted optical depths cannot be understood in terms of statistical
fluctuations. In these experiments there is typically a clump of particles
crossing the line of sight to the hypothetical LMC. These clumps can be either
gravitationally bound systems or transient phenomena in a galaxy that is still
undergoing phase mixing. Substructure of this type, if present in the Galactic
distribution of Machos, can lead to large systematic errors in the analysis of
microlensing experiments. We also describe how hypothetical WIMP and axion
detection experiments might be conducted in a simulated N-body galaxy.Comment: 18 pages of text (LaTeX, AASTeX) with 12 figures. submitted to the
Astrophysical Journa
Generation of eigenstates using the phase-estimation algorithm
The phase estimation algorithm is so named because it allows the estimation
of the eigenvalues associated with an operator. However it has been proposed
that the algorithm can also be used to generate eigenstates. Here we extend
this proposal for small quantum systems, identifying the conditions under which
the phase estimation algorithm can successfully generate eigenstates. We then
propose an implementation scheme based on an ion trap quantum computer. This
scheme allows us to illustrate two simple examples, one in which the algorithm
effectively generates eigenstates, and one in which it does not.Comment: 5 pages, 3 Figures, RevTeX4 Introduction expanded, typos correcte
Demonstration of Entanglement of Electrostatically Coupled Singlet-Triplet Qubits
Quantum computers have the potential to solve certain interesting problems
significantly faster than classical computers. To exploit the power of a
quantum computation it is necessary to perform inter-qubit operations and
generate entangled states. Spin qubits are a promising candidate for
implementing a quantum processor due to their potential for scalability and
miniaturization. However, their weak interactions with the environment, which
leads to their long coherence times, makes inter-qubit operations challenging.
We perform a controlled two-qubit operation between singlet-triplet qubits
using a dynamically decoupled sequence that maintains the two-qubit coupling
while decoupling each qubit from its fluctuating environment. Using state
tomography we measure the full density matrix of the system and determine the
concurrence and the fidelity of the generated state, providing proof of
entanglement
Effective Hamiltonian Theory and Its Applications in Quantum Information
This paper presents a useful compact formula for deriving an effective
Hamiltonian describing the time-averaged dynamics of detuned quantum systems.
The formalism also works for ensemble-averaged dynamics of stochastic systems.
To illustrate the technique we give examples involving Raman processes,
Bloch-Siegert shifts and Quantum Logic Gates.Comment: 5 pages, 3 figures, to be published in Canadian Journal of Physic
Mass Density Profiles of LSB Galaxies
We derive the mass density profiles of dark matter halos that are implied by
high spatial resolution rotation curves of low surface brightness galaxies. We
find that at small radii, the mass density distribution is dominated by a
nearly constant density core with a core radius of a few kpc. For rho(r) ~ r^a,
the distribution of inner slopes a is strongly peaked around a = -0.2. This is
significantly shallower than the cuspy a < -1 halos found in CDM simulations.
While the observed distribution of alpha does have a tail towards such extreme
values, the derived value of alpha is found to depend on the spatial resolution
of the rotation curves: a ~ -1 is found only for the least well resolved
galaxies. Even for these galaxies, our data are also consistent with constant
density cores (a = 0) of modest (~ 1 kpc) core radius, which can give the
illusion of steep cusps when insufficiently resolved. Consequently, there is no
clear evidence for a cuspy halo in any of the low surface brightness galaxies
observed.Comment: To be published in ApJ Letters. 6 pages. Uses aastex and
emulateapj5.sty Typo in Eq 1 fixe
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