4,252 research outputs found
A Chandra Snapshot Survey for 3C Radio Galaxies with redshifts between 0.3 and 0.5
This paper contains an analysis of short Chandra observations of 19 3C
sources with redshifts between 0.3 and 0.5 not previously observed in the
X-rays. This sample is part of a project to obtain Chandra data for all of the
extragalactic sources in the 3C catalogue. Nuclear X-ray intensities as well as
any X-ray emission associated with radio jet knots, hotspots or lobes have been
measured in 3 energy bands: soft, medium and hard. Standard X-ray spectral
analysis for the 4 brightest nuclei has been also performed. X-ray emission was
detected for all the nuclei of the radio sources in the current sample with the
exception of 3C 435A. There is one compact steep spectrum (CSS) source while
all the others are FRII radio galaxies. X-ray emission from two galaxy clusters
(3C 19 and 3C 320); from 6 hotspots in 4 radio galaxies (3C 16, 3C 19, 3C
268.2, 3C 313); and extended X-ray emission on kpc scales in 3C 187 and 3C 313,
has been detected.Comment: 33 pages, 22 figures, 7 tables, accepted for publication on the ApJ
Supplement Series. arXiv admin note: text overlap with arXiv:1210.602
Pseudogap induced by short-range spin correlations in a doped Mott insulator
We study the evolution of a Mott-Hubbard insulator into a correlated metal
upon doping in the two-dimensional Hubbard model using the Cellular Dynamical
Mean Field Theory. Short-range spin correlations create two additional bands
apart from the familiar Hubbard bands in the spectral function. Even a tiny
doping into this insulator causes a jump of the Fermi energy to one of these
additional bands and an immediate momentum dependent suppression of the
spectral weight at this Fermi energy. The pseudogap is closely tied to the
existence of these bands. This suggests a strong-coupling mechanism that arises
from short-range spin correlations and large scattering rates for the pseudogap
phenomenon seen in several cuprates.Comment: 6 pages, 6 figure
Third order superintegrable systems separating in polar coordinates
A complete classification is presented of quantum and classical
superintegrable systems in that allow the separation of variables in
polar coordinates and admit an additional integral of motion of order three in
the momentum. New quantum superintegrable systems are discovered for which the
potential is expressed in terms of the sixth Painlev\'e transcendent or in
terms of the Weierstrass elliptic function
The Ratio of Helium- to Hydrogen-Atmosphere White Dwarfs: Direct Evidence for Convective Mixing
We determine the ratio of helium- to hydrogen-atmosphere white dwarf stars as
a function of effective temperature from a model atmosphere analysis of the
infrared photometric data from the Two Micron All Sky Survey combined with
available visual magnitudes. Our study surpasses any previous analysis of this
kind both in terms of the accuracy of the Teff determinations as well as the
size of the sample. We observe that the ratio of helium- to hydrogen-atmosphere
white dwarfs increases gradually from a constant value of ~0.25 between Teff =
15,000 K and 10,000 K to a value twice as large in the range 10,000 > Teff >
8000 K, suggesting that convective mixing, which occurs when the bottom of the
hydrogen convection zone reaches the underlying convective helium envelope, is
responsible for this gradual transition. The comparison of our results with an
approximate model used to describe the outcome of this convective mixing
process implies hydrogen mass layers in the range log M_H/M_tot = -10 to -8 for
about 15% of the DA stars that survived the DA to DB transition near Teff ~
30,000 K, the remainder having presumably more massive layers above log
M_H/M_tot ~ -6.Comment: 30 pages, 11 figures, accepted for publication in the Astrophysical
Journa
Symmetries of differential-difference dynamical systems in a two-dimensional lattice
Classification of differential-difference equation of the form
are considered
according to their Lie point symmetry groups. The set represents the
point and its six nearest neighbors in a two-dimensional triangular
lattice. It is shown that the symmetry group can be at most 12-dimensional for
abelian symmetry algebras and 13-dimensional for nonsolvable symmetry algebras.Comment: 24 pages, 1 figur
A shrinking Compact Symmetric Object: J11584+2450?
We present multi-frequency multi-epoch Very Long Baseline Array (VLBA)
observations of J11584+2450. These observations clearly show this source,
previously classified as a core-jet, to be a compact symmetric object (CSO).
Comparisons between these new data and data taken over the last 9 years shows
the edge brightened hot spots retreating towards the core (and slightly to the
west) at approximately 0.3c. Whether this motion is strictly apparent or
actually physical in nature is discussed, as well as possible explanations, and
what implications a physical contraction of J11584+2450 would have for current
CSO models.Comment: 16 pages, 6 figures, 5 tables. Accepted for publication in Ap
Superintegrable systems with spin and second-order integrals of motion
We investigate a quantum nonrelativistic system describing the interaction of
two particles with spin 1/2 and spin 0, respectively. We assume that the
Hamiltonian is rotationally invariant and parity conserving and identify all
such systems which allow additional integrals of motion that are second order
matrix polynomials in the momenta. These integrals are assumed to be scalars,
pseudoscalars, vectors or axial vectors. Among the superintegrable systems
obtained, we mention a generalization of the Coulomb potential with scalar
potential and spin orbital one
.Comment: 32 page
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