16,100 research outputs found
The Distance of the First Overtone RR Lyrae Variables in the MACHO LMC Database: A New Method to Correct for the Effects of Crowding
Previous studies have indicated that many of the RR Lyrae variables in the
LMC have properties similar to the ones in the Galactic globular cluster M3.
Assuming that the M3 RR Lyrae variables follow the same relationships among
period, temperature, amplitude and Fourier phase parameter phi31 as their LMC
counterparts, we have used the M3 phi31-logP relation to identify the M3-like
unevolved first overtone RR Lyrae variables in 16 fields near the LMC bar. The
temperatures of these variables were calculated from the M3 logP-logTe relation
so that the extinction could be derived for each star separately. Since blended
stars have lower amplitudes for a given period, the period amplitude relation
should be a useful tool for identifying which stars are affected by crowding.
We find that the low amplitude stars are brighter. We remove them from the
sample and derive an LMC distance modulus 18.49+/-0.11.Comment: 30 pages, 7 figures, accepted for publication in the Astronomical
Journa
Bounds on the force between black holes
We treat the problem of N interacting, axisymmetric black holes and obtain
two relations among physical parameters of the system including the force
between the black holes. The first relation involves the total mass, the
angular momenta, the distances and the forces between the black holes. The
second one relates the angular momentum and area of each black hole with the
forces acting on it.Comment: 13 pages, no figure
The Variable Stars of the Draco Dwarf Spheroidal Galaxy - Revisited
We present a CCD survey of variable stars in the Draco dwarf spheroidal
galaxy. This survey, which has the largest areal coverage since the original
variable star survey by Baade & Swope, includes photometry for 270 RR Lyrae
stars, 9 anomalous Cepheids, 2 eclipsing binaries, and 12 slow, irregular red
variables, as well as 30 background QSOs. Twenty-six probable double-mode RR
Lyrae stars were identified. Observed parameters, including mean V and I
magnitudes, V amplitudes, and periods, have been derived. Photometric
metallicities of the ab-type RR Lyrae stars were calculated according to the
method of Jurcsik & Kovacs, yielding a mean metallicity of = -2.19 +/-
0.03. The well known Oosterhoff intermediate nature of the RR Lyrae stars in
Draco is reconfirmed, although the double-mode RR Lyrae stars with one
exception have properties similar to those found in Oosterhoff type II globular
clusters. The period-luminosity relation of the anomalous Cepheids is
rediscussed with the addition of the new Draco anomalous Cepheids.Comment: Accepted to AJ. 61 pages, 14 figures, 10 table
Generalized Massive Gravity and Galilean Conformal Algebra in two dimensions
Galilean conformal algebra (GCA) in two dimensions arises as contraction of
two copies of the centrally extended Virasoro algebra ( with ). The central charges of
GCA can be expressed in term of Virasoro central charges. For finite and
non-zero GCA central charges, the Virasoro central charges must behave as
asymmetric form . We propose that, the bulk
description for 2d GCA with asymmetric central charges is given by general
massive gravity (GMG) in three dimensions. It can be seen that, if the
gravitational Chern-Simons coupling behaves as of order
O() or (), the central charges
of GMG have the above dependence. So, in non-relativistic scaling
limit , we calculated GCA parameters and finite
entropy in term of gravity parameters mass and angular momentum of GMG.Comment: 9 page
Force indeterminacy in the jammed state of hard disks
Granular packings of hard discs are investigated by means of contact dynamics
which is an appropriate technique to explore the allowed force-realizations in
the space of contact forces. Configurations are generated for given values of
the friction coefficient, and then an ensemble of equilibrium forces is found
for fixed contacts. We study the force fluctuations within this ensemble. In
the limit of zero friction the fluctuations vanish in accordance with the
isostaticity of the packing. The magnitude of the fluctuations has a
non-monotonous friction dependence. The increase for small friction can be
attributed to the opening of the angle of the Coulomb cone, while the decrease
as friction increases is due to the reduction of connectivity of the
contact-network, leading to local, independent clusters of indeterminacy. We
discuss the relevance of indeterminacy to packings of deformable particles and
to the mechanical response properties.Comment: 4 pages, 3 figures. Minor changes, journal reference adde
Inelastic Collapse of Three Particles
A system of three particles undergoing inelastic collisions in arbitrary
spatial dimensions is studied with the aim of establishing the domain of
``inelastic collapse''---an infinite number of collisions which take place in a
finite time. Analytic and simulation results show that for a sufficiently small
restitution coefficient, , collapse can
occur. In one dimension, such a collapse is stable against small perturbations
within this entire range. In higher dimensions, the collapse can be stable
against small variations of initial conditions, within a smaller range,
.Comment: 6 pages, figures on request, accepted by PR
Extracting the depolarization coefficient D_NN from data measured with a full acceptance detector
The spin transfer from vertically polarized beam protons to Lambda or Sigma
hyperons of the associated strangeness production pp -> pK Lambda (Sigma) is
described with the depolarization coefficient D_NN. As the polarization of the
hyperons is determined by their weak decays, detectors, which have a large
acceptance for the decay particles, are needed. In this paper a formula is
derived, which describes the depolarization coefficient D_NN by count rates of
a 4 pi detector. It is shown, that formulas, which are given in publications
for detectors with restricted acceptance, are specific cases of this formula
for a 4 pi detector.Comment: Accepted for publication by Nuclear Instruments and Methods in
Physics Research Section
The high-intensity hyperon beam at CERN
A high-intensity hyperon beam was constructed at CERN to deliver Sigma- to
experiment WA89 at the Omega facility and operated from 1989 to 1994. The setup
allowed rapid changeover between hyperon and conventional hadron beam
configurations. The beam provided a Sigma-flux of 1.4 x 10^5 per burst at mean
momenta between 330 and 345 Gev/c, produced by about 3 x 10^10 protons of 450
GeV/c . At the experiment target the beam had a Sigma-/pi- ratio close to 0.4
and a size of 1.6 x 3.7 cm^2. The beam particle trajectories and their momenta
were measured with a scintillating fibre hodoscope in the beam channel and a
silicon microstrip detector at the exit of the channel. A fast transition
radiation detector was used to identify the pion component of the beam.Comment: 20 pages, 13 figures. Submitted to Nucl. Instr. Meth.
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