177 research outputs found
Note on Inversion Formula to Determine Binary Elements by Astrometry
Simplified solutions to determine binary elements by astrometry were obtained
in terms of elementary functions (Asada et al. 2004), and therefore require
neither iterative nor numerical methods. In the framework of the simplified
solution, this paper discusses the remaining two parameters of the time of
periastron passage and the longitude of ascending node in order to complete the
solution. We thus clarify a difference between the simplified solution and
other analytical methods.Comment: 12 pages, 4 figures, 2 tables; accepted for publication in PAS
Observation of Gravitational Lensing in the Clumpy Universe
We discuss how inhomogeneities of the universe affect observations of the
gravitational lensing; (1) the bending angle, (2) the lensing statistics and
(3) the time delay. In order to take account of the inhomogeneities, the
Dyer-Roeder distance is used, which includes a parameter representing the
clumpiness of the matter along the line of sight. It is shown analytically that
all three combinations of distances appearing in the above observations (1)-(3)
are monotonic with respect to the clumpiness in general, for any given set of
the density parameter, cosmological constant and redshifts of the lens and the
source. Some implications of this result for the observation are presented; the
clumpiness decreases both the bending angle and the lensing event rate, while
it increases the time delay. We also discuss cosmological tests using the
gravitational lensing in the clumpy universe.Comment: 12 pages, LaTeX(aaspp4); accepted for publication in The
Astrophysical Journa
The Light-cone Effect on the Shapiro Time Delay
We investigate the light-cone effect on the Shapiro time delay. The extra
time delay caused by Jupiter on the 8th of September 2002 can be measured by
advanced VLBI (very long baseline interferometry). Our expression for the delay
is in complete agreement with that of Kopeikin (2001), in which he argued that
the excess time delay was due to the propagation of gravity. The present
letter, however, shows that the excess comes from nothing but the propagation
of light, namely the light-cone effect. To make a robust confirmation of
general relativity by the coming Jupiter event, it is important to take account
of the light-cone effect on the Shapiro time delay.Comment: 5 pages; accepted for publication in ApJ Letter
Deflection angle of light in an Ellis wormhole geometry
We reexamine the light deflection by an Ellis wormhole. The bending angle as
a function of the ratio between the impact parameter and the throat radius of
the wormhole is obtained in terms of a complete elliptic integral of the first
kind. This result immediately yields asymptotic expressions in the weak field
approximation. It is shown that an expression for the deflection angle derived
(and used) in recent papers is valid at the leading order but it breaks down at
the next order because of the nontrivial spacetime topology.Comment: 3 pages, accepted by PR
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