1,996 research outputs found
Gravitomagnetism and the Earth-Mercury range
We numerically work out the impact of the general relativistic Lense-Thirring
effect on the Earth-Mercury range caused by the gravitomagnetic field of the
rotating Sun. The peak-to peak nominal amplitude of the resulting time-varying
signal amounts to 1.75 10^1 m over a temporal interval 2 yr. Future
interplanetary laser ranging facilities should reach a cm-level in ranging to
Mercury over comparable timescales; for example, the BepiColombo mission, to be
launched in 2014, should reach a 4.5 - 10 cm level over 1 - 8 yr. We looked
also at other Newtonian (solar quadrupole mass moment, ring of the minor
asteroids, Ceres, Pallas, Vesta, Trans-Neptunian Objects) and post-Newtonian
(gravitoelectric Schwarzschild solar field) dynamical effects on the
Earth-Mercury range. They act as sources of systematic errors for the
Lense-Thirring signal which, in turn, if not properly modeled, may bias the
recovery of some key parameters of such other dynamical features of motion.
Their nominal peak-to-peak amplitudes are as large as 4 10^5 m (Schwarzschild),
3 10^2 m (Sun's quadrupole), 8 10^1 m (Ceres, Pallas, Vesta), 4 m (ring of
minor asteroids), 8 10^-1 m (Trans-Neptunian Objects). Their temporal patterns
are different with respect to that of the gravitomagnetic signal.Comment: LaTex2e, 19 pages, 2 tables, 6 figures. Small typo in pag. 1406 of
the published version fixe
Analytic Kramer kernels, Lagrange-type interpolation series and de Branges spaces
The classical Kramer sampling theorem provides a method for obtaining orthogonal sampling formulas. In particular, when the involved kernel is analytic in the sampling parameter it can be stated in an abstract setting of reproducing kernel Hilbert spaces of entire functions which includes as a particular case the classical Shannon sampling theory. This abstract setting allows us to obtain a sort of converse result and to characterize when the sampling formula associated with an analytic Kramer kernel can be expressed as a Lagrange-type interpolation series. On the other hand, the de Branges spaces of entire functions satisfy orthogonal sampling formulas which can be written as Lagrange-type interpolation series. In this work some links between all these ideas are established
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The Zero-Removing Property and Lagrange-Type Interpolation Series
The classical Kramer sampling theorem, which provides a method for obtaining orthogonal sampling formulas, can be formulated in a more general nonorthogonal setting. In this setting, a challenging problem is to characterize the situations when the obtained nonorthogonal sampling formulas can be expressed as Lagrange-type interpolation series. In this article a necessary and sufficient condition is given in terms of the zero removing property. Roughly speaking, this property concerns the stability of the sampled functions on removing a finite number of their zeros
First preliminary tests of the general relativistic gravitomagnetic field of the Sun and new constraints on a Yukawa-like fifth force from planetary data
The general relativistic Lense-Thirring precessions of the perihelia of the
inner planets of the Solar System are about 10^-3 arcseconds per century.
Recent improvements in planetary orbit determination may yield the first
observational evidence of such a tiny effect. Indeed, corrections to the known
perihelion rates of -0.0036 +/- 0.0050, -0.0002 +/- 0.0004 and 0.0001 +/-
0.0005 arcseconds per century were recently estimated by E.V. Pitjeva for
Mercury, the Earth and Mars, respectively, on the basis of the EPM2004
ephemerides and a set of more than 317,000 observations of various kinds. The
predicted relativistic Lense-Thirring precessions for these planets are
-0.0020, -0.0001 and -3 10^-5 arcseconds per century, respectively and are
compatible with the determined perihelia corrections. The relativistic
predictions fit better than the zero-effect hypothesis, especially if a
suitable linear combination of the perihelia of Mercury and the Earth, which a
priori cancels out any possible bias due to the solar quadrupole mass moment,
is considered. However, the experimental errors are still large. Also the
latest data for Mercury processed independently by Fienga et al. with the INPOP
ephemerides yield preliminary insights about the existence of the solar
Lense-Thirring effect. The data from the forthcoming planetary mission
BepiColombo will improve our knowledge of the orbital motion of this planet
and, consequently, the precision of the measurement of the Lense-Thirring
effect. As a by-product of the present analysis, it is also possible to
constrain the strength of a Yukawa-like fifth force to a 10^-12-10^-13 level at
scales of about one Astronomical Unit (10^11 m).Comment: LaTex, 22 pages, 1 figure, 5 tables, 62 references. To appear in
Planetary and Space Scienc
Gravitomagnetic Accelerators
We study a simple class of time-dependent rotating Ricci-flat cylindrically
symmetric spacetime manifolds whose geodesics admit gravitomagnetic jets. The
helical paths of free test particles in these jets up and down parallel to the
rotation axis are analogous to those of charged particles in a magnetic field.
The jets are attractors. The jet speed asymptotically approaches the speed of
light. In effect, such source-free spacetime regions act as "gravitomagnetic
accelerators".Comment: 4 pages, 2 figures; v2: reference added; v3: slightly expanded
version accepted for publication in Phys. Lett.
Regular singular Sturm-Liouville operators and their zeta-determinants
We consider Sturm-Liouville operators on the line segment [0, 1] with general
regular singular potentials and separated boundary conditions. We establish
existence and a formula for the associated zeta-determinant in terms of the
Wronski- determinant of a fundamental system of solutions adapted to the
boundary conditions. This generalizes the earlier work of the first author,
treating general regular singular potentials but only the Dirichlet boundary
conditions at the singular end, and the recent results by Kirsten-Loya-Park for
general separated boundary conditions but only special regular singular
potentials.Comment: 38 pages, 2 figures; Completely revised according to the referees
comprehensive suggestions; v3: minor corrections, accepted for publication in
Journal of Functional Analysi
Search for blue compact dwarf galaxies during quiescence II: metallicities of gas and stars, ages, and star-formation rates
We examine the metallicity and age of a large set of SDSS/DR6 galaxies that
may be Blue Compact Dwarf (BCD) galaxies during quiescence (QBCDs).The
individual spectra are first classified and then averaged to reduce noise. The
metallicity inferred from emission lines (tracing ionized gas) exceeds by ~0.35
dex the metallicity inferred from absorption lines (tracing stars). Such a
small difference is significant according to our error budget estimate. The
same procedure was applied to a reference sample of BCDs, and in this case the
two metallicities agree, being also consistent with the stellar metallicity in
QBCDs. Chemical evolution models indicate that the gas metallicity of QBCDs is
too high to be representative of the galaxy as a whole, but it can represent a
small fraction of the galactic gas, self enriched by previous starbursts. The
luminosity weighted stellar age of QBCDs spans the whole range between 1 and 10
Gyr, whereas it is always smaller than 1 Gyr for BCDs. Our stellar ages and
metallicities rely on a single stellar population spectrum fitting procedure,
which we have specifically developed for this work using the stellar library
MILES.Comment: Accepted for publication in ApJ. 20 pages. 16 figures (corrected
typos
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