1,690 research outputs found
IRAS asteroid families
The Infrared Astronomical Satellite (IRAS) sampled the entire asteroid population at wavelengths from 12 to 100 microns during its 1983 all sky survey. The IRAS Minor Planet Survey (IMPS) includes updated results for more recently numbered as well as other additional asteroids with reliable orbital elements. Albedos and diameters were derived from the observed thermal emission and assumed absolute visual magnitudes and then entered into the IMPS database at the Infrared Processing and Analysis Center (IPAC) for members of the Themis, Eos, Koronis and Maria asteroid families and compared with their visual colors. The IMPS results for the small (down to about 20 km) asteroids within these major families confirm trends previously noted for their larger members. Each of these dynamical families which are defined by their similar proper elements appears to have homogeneous physical properties
Cosmic Parallax in Ellipsoidal Universe
The detection of a time variation of the angle between two distant sources
would reveal an anisotropic expansion of the Universe. We study this effect of
"cosmic parallax" within the "ellipsoidal universe" model, namely a particular
homogeneous anisotropic cosmological model of Bianchi type I, whose attractive
feature is the potentiality to account for the observed lack of power of the
large-scale cosmic microwave background anisotropy. The preferred direction in
the sky, singled out by the axis of symmetry inherent to planar symmetry of
ellipsoidal universe, could in principle be constrained by future cosmic
parallax data. However, that will be a real possibility if and when the
experimental accuracy will be enhanced at least by two orders of magnitude.Comment: 9 pages, 2 figures, 1 table. Revised version to match published
version. References adde
Ellipsoidal Universe Can Solve The CMB Quadrupole Problem
The recent three-year WMAP data have confirmed the anomaly concerning the low
quadrupole amplitude compared to the best-fit \Lambda CDM prediction. We show
that, allowing the large-scale spatial geometry of our universe to be
plane-symmetric with eccentricity at decoupling or order 10^{-2}, the
quadrupole amplitude can be drastically reduced without affecting higher
multipoles of the angular power spectrum of the temperature anisotropy.Comment: 4 pages, 2 figures, minor changes, reference added, to appear in
Phys. Rev. Let
A remark on the BRST symmetry in the Gribov-Zwanziger theory
We show that the soft breaking of the BRST symmetry arising in the
Gribov-Zwanziger theory can be converted into a linear breaking upon
introduction of a set of BRST quartets of auxiliary fields. Due to its
compatibility with the Quantum Action Principle, the linearly broken BRST
symmetry can be directly converted into a suitable set of useful Slavnov-Taylor
identities. As a consequence, it turns out that the renormalization aspects of
the Gribov-Zwanziger theory can be addressed by means of the cohomology of a
nilpotent local operatorComment: 11 pages, final version to appear in Phys. Rev.
Anisotropic dark energy and ellipsoidal universe
A cosmological model with anisotropic dark energy is analyzed. The amount of
deviation from isotropy of the equation of state of dark energy, the skewness
\delta, generates an anisotropization of the large-scale geometry of the
Universe, quantifiable by means of the actual shear \Sigma_0. Requiring that
the level of cosmic anisotropization at the time of decoupling is such to solve
the "quadrupole problem" of cosmic microwave background radiation, we find that
|\delta| \sim 10^{-4} and |\Sigma_0| \sim 10^{-5}, compatible with existing
limits derived from the magnitude-redshift data on type Ia supernovae.Comment: 10 pages, 3 figures. Revised version to match published version.
References adde
An enhanced sea-ice thermodynamic model applied to the Baltic sea
A refined Semtner 0-layer sea-ice model (ESIM1) is presented and applied to the Baltic landfast sea-ice. The physical model is capable of simulating seasonal changes of snow and ice thickness. Particular attention is paid to reproducing the snow-ice and the super-imposed-ice formation which play important roles in the total mass balance of the Baltic sea-ice. The model prognostic variables include all kinds of ice and snow layers that may be present during a Baltic landfast ice season and, in general, in every coastal area of an ice-covered ocean. The assessment of the model capabilities was done for 1979–1993 for four different stations in the Baltic Sea. A sensitivity test stresses the relevant role of some of the physical parameters, such as the oceanic heat flux, while a scenario analysis highlights the robustness of the model to perturbed physical forcing. Our results show that one of the key variables in modelling sea-ice thermodynamics is the snow layer and its metamorphism, and including the meteoric ice dynamics into a sea ice model is relevant to properly simulate any ice season, also in view of climate change scenario
Mass and density of B-type asteroid (702) Alauda
Observations with the adaptive optics system on the Very Large Telescope
reveal that outer main belt asteroid (702) Alauda has a small satellite with
primary to secondary diameter ratio of 56. The secondary revolves around
the primary in 4.9143 0.007 days at a distance of 1227 24 km,
yielding a total system mass of (6.057 0.36) 10 kg.
Combined with an IRAS size measurement, our data yield a bulk density for this
B-type asteroid of 1570 500 kg~m.Comment: In press, ApJ 2011. 6 pages, 4 figure
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