78,678 research outputs found
Classifying orbits of the affine group over the integers
For each , let
be the affine group over the integers. For every point let Let be the subgroup
of the additive group generated by . If
then . Thus, is a complete classifier of . By
contrast, if , knowledge of alone is not sufficient
in general to uniquely recover : as a matter of fact,
determines precisely different orbits,
where is the denominator of the smallest positive nonzero rational in
and is Euler function. To get a complete classification, rational
polyhedral geometry provides an integer
such that iff
Prospecting Period Measurements with LSST - Low Mass X-ray Binaries as a Test Case
The Large Synoptic Survey Telescope (LSST) will provide for unbiased sampling
of variability properties of objects with mag 24. This should allow for
those objects whose variations reveal their orbital periods (), such
as low mass X-ray binaries (LMXBs) and related objects, to be examined in much
greater detail and with uniform systematic sampling. However, the baseline LSST
observing strategy has temporal sampling that is not optimised for such work in
the Galaxy. Here we assess four candidate observing strategies for measurement
of in the range 10 minutes to 50 days. We simulate multi-filter
quiescent LMXB lightcurves including ellipsoidal modulation and stochastic
flaring, and then sample these using LSST's operations simulator (OpSim) over
the (mag, ) parameter space, and over five sightlines sampling a range
of possible reddening values. The percentage of simulated parameter space with
correctly returned periods ranges from 23 %, for the current baseline
strategy, to 70 % for the two simulated specialist strategies. Convolving
these results with a distribution, a modelled Galactic spatial
distribution and reddening maps, we conservatively estimate that the most
recent version of the LSST baseline strategy will allow determination
for 18 % of the Milky Way's LMXB population, whereas strategies that do
not reduce observations of the Galactic Plane can improve this dramatically to
32 %. This increase would allow characterisation of the full binary
population by breaking degeneracies between suggested distributions
in the literature. Our results can be used in the ongoing assessment of the
effectiveness of various potential cadencing strategies.Comment: Replacement after addressing minor corrections from the referee -
mainly improvements in clarificatio
Gamma-ray Timing of Redback PSR J2339-0533: Hints for Gravitational Quadrupole Moment Changes
We present the results of precision gamma-ray timing measurements of the
binary millisecond pulsar PSR J23390533, an irradiating system of "redback"
type, using data from the Fermi Large Area Telescope. We describe an optimized
analysis method to determine a long-term phase-coherent timing solution
spanning more than six years, including a measured eccentricity of the binary
orbit and constraints on the proper motion of the system. A major result of
this timing analysis is the discovery of an extreme variation of the nominal
4.6-hour orbital period over time, showing alternating epochs of
decrease and increase. We inferred a cyclic modulation of with an
approximate cycle duration of 4.2 years and a modulation amplitude of . Considering different possible
physical causes, the observed orbital-period modulation most likely results
from a variable gravitational quadrupole moment of the companion star due to
cyclic magnetic activity in its convective zone.Comment: 9 pages, 2 figure
Further study on 5q configuration states in the chiral SU(3) quark model
The structure of the configuration states with strangeness
is further studied in the chiral SU(3) quark model based on our
previous work. We calculate the energies of fifteen low configurations of the
system, four lowest configurations of with
partition , four of with
partition and seven of
with partition . Some modifications are
made in this further study, i.e., the orbital wave function is extended as an
expansion of 4 different size harmonic oscillator forms; three various forms
(quadratic, linear and error function form) of the color confinement potential
are considered; the states with partition are added, which are unnegligible in the case and were
not considered in our previous paper, further the mixing between configurations
and is
also investigated. The results show that the T=0 state is still always the
lowest one for both and states, and
state is always lower than that of .
All of these modifications can only offer several tens to hundred MeV effect,
and the theoretical value of the lowest state is still about 245 MeV higher
than the experimental mass of . It seems to be difficult to get the
calculated mass close to the observed one with the reasonable parameters in the
framework of the chiral SU(3) quark model when the model space is chosen as a
cluster.Comment: 16 page
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