117 research outputs found
A precise modeling of Phoebe's rotation
Although the rotation of some Saturn's satellites in spin-orbit has already
been studied by several authors, this is not the case of the rotation of
Phoebe, which has the particularity of being non resonant. The purpose of the
paper is to determine for the first time and with precision its
precession-nutation motion. We adopt an Hamiltonian formalism of the motion of
rotation of rigid celestial body set up by Kinoshita (1977) based on Andoyer
variables and canonical equations. First we calculate Phoebe's obliquity at
J2000,0 from available astronomical data as well as the gravitational
perturbation due to Saturn on Phoebe rotational motion. Then we carry out a
numerical integration and we compare our results for the precession rate and
the nutation coefficients with pure analytical model. Our results for Phoebe
obliquity (23{\deg}95) and Phoebe precession rate (5580".65/cy) are very close
to the respective values for the Earth. Moreover the amplitudes of the
nutations (26" peak to peak for the nutaton in longitude and 8" for the
nutation in obliquity) are of the same order as the respective amplitudes for
the Earth. We give complete tables of nutation, obtained from a FFT analysis
starting from the numerical signals. We show that a pure analytical model of
the nutation is not accurate due to the fact that Phoebe orbital elements e, M
and Ls are far from having a simple linear behaviour. The precession and
nutation of Phoebe have been calculated for the first time in this paper. We
should keep on the study in the future by studying the additional gravitational
effects of the Sun, of the large satellites as Titan, as well as Saturn
dynamical ellipticity.Comment: 11 pages,15 figures, accepted for publication in A&
Fluctuations of Matrix Entries of Regular Functions of Wigner Matrices
We study the fluctuations of the matrix entries of regular functions of
Wigner random matrices in the limit when the matrix size goes to infinity. In
the case of the Gaussian ensembles (GOE and GUE) this problem was considered by
A.Lytova and L.Pastur in J. Stat. Phys., v.134, 147-159 (2009). Our results are
valid provided the off-diagonal matrix entries have finite fourth moment, the
diagonal matrix entries have finite second moment, and the test functions have
four continuous derivatives in a neighborhood of the support of the Wigner
semicircle law.Comment: minor corrections; the manuscript will appear in the Journal of
Statistical Physic
An Empirical Explanation of the Anomalous Increases in the Astronomical Unit and the Lunar Eccentricity
Both the recently reported anomalous secular increase of the astronomical
unit, of the order of a few cm yr^-1, and of the eccentricity of the lunar
orbit e_ = (9+/-3) 10^-12 yr^-1 can be phenomenologically explained by
postulating that the acceleration of a test particle orbiting a central body,
in addition to usual Newtonian component, contains a small additional radial
term proportional to the radial projection vr of the velocity of the particle's
orbital motion. Indeed, it induces secular variations of both the semi-major
axis a and the eccentricity e of the test particle's orbit. In the case of the
Earth and the Moon, they numerically agree rather well with the measured
anomalies if one takes the numerical value of the coefficient of
proportionality of the extra-acceleration approximately equal to that of the
Hubble parameter H0 = 7.3 10^-11 yr^-1.Comment: Latex2e, no figures, no tables, 9 pages, 51 references. Published in
The Astronomical Journal (AJ
On universality of local edge regime for the deformed Gaussian Unitary Ensemble
We consider the deformed Gaussian ensemble in which
is a hermitian matrix (possibly random) and is the Gaussian
unitary random matrix (GUE) independent of . Assuming that the
Normalized Counting Measure of converges weakly (in probability if
random) to a non-random measure with a bounded support and assuming
some conditions on the convergence rate, we prove universality of the local
eigenvalue statistics near the edge of the limiting spectrum of .Comment: 25 pages, 2 figure
The influence of Galactic aberration on precession parameters determined from VLBI observations
The influence of proper motions of sources due to Galactic aberration on
precession models based on VLBI data is determined. Comparisons of the linear
trends in the coordinates of the celestial pole obtained with and without
taking into account Galactic aberration indicate that this effect can reach 20
as per century, which is important for modern precession models. It is
also shown that correcting for Galactic aberration influences the derived
parameters of low-frequency nutation terms. It is therefore necessary to
correct for Galactic aberration in the reduction of modern astrometric
observations
The empirical Earth rotation model from VLBI observations
AIMS: An alternative to the traditional method for modeling kinematics of the
Earth's rotation is proposed. The purpose of developing the new approach is to
provide a self-consistent and simple description of the Earth's rotation in a
way that can be estimated directly from observations without using intermediate
quantities.
METHODS: Instead of estimating the time series of pole coordinates, the
UT1--TAI angles, their rates, and the daily offsets of nutation, it is proposed
to estimate coefficients of the expansion of a small perturbational rotation
vector into basis functions. The resulting transformation from the terrestrial
coordinate system to the celestial coordinate system is formulated as a product
of an a priori matrix of a finite rotation and an empirical vector of a
residual perturbational rotation. In the framework of this approach, the
specific choice of the a priori matrix is irrelevant, provided the angles of
the residual rotation are small enough to neglect their squares. The
coefficients of the expansion into the B-spline and Fourier bases, together
with estimates of other nuisance parameters, are evaluated directly from
observations of time delay or time range in a single least square solution.
RESULTS: This approach was successfully implemented in a computer program for
processing VLBI observations. The dataset from 1984 through 2006 was analyzed.
The new procedure adequately represents the Earth's rotation, including slowly
varying changes in UT1--TAI and polar motion, the forced nutations, the free
core nutation, and the high frequency variations of polar motion and UT1.Comment: 15 pages, 10 figures, Published in Astronomy and Astrophysics. For
numerical tables see http://vlbi.gsfc.nasa.gov/er
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