56,815 research outputs found
Additive Entropies of degree-q and the Tsallis Entropy
The Tsallis entropy is shown to be an additive entropy of degree-q that
information scientists have been using for almost forty years. Neither is it a
unique solution to the nonadditive functional equation from which random
entropies are derived. Notions of additivity, extensivity and homogeneity are
clarified. The relation between mean code lengths in coding theory and various
expressions for average entropies is discussed.Comment: 13 page
SINFONI's take on Star Formation, Molecular Gas, and Black Hole Masses in AGN
We present some preliminary (half-way) results on our adaptive optics
spectroscopic survey of AGN at spatial scales down to 0.085arcsec. Most of the
data were obtained with SINFONI which provides integral field capability at a
spectral resolution of R~4000. The themes on which we focus in this
contribution are: star formation around the AGN, the properties of the
molecular gas and its relation to the torus, and the mass of the black hole.Comment: 5 pages, 2 figures. To appear in Science Perspectives for 3D
Spectroscopy. ESO Astrophysics Symposia. Ed by M. Kissler-Patig, M. Roth and
J. Wals
The destruction of inner planetary systems during high-eccentricity migration of gas giants
Hot Jupiters are giant planets on orbits a few hundredths of an AU. They do
not share their system with low-mass close-in planets, despite these latter
being exceedingly common. Two migration channels for hot Jupiters have been
proposed: through a protoplanetary gas disc or by tidal circularisation of
highly-eccentric planets. We show that highly-eccentric giant planets that will
become hot Jupiters clear out any low-mass inner planets in the system,
explaining the observed lack of such companions to hot Jupiters. A less common
outcome of the interaction is that the giant planet is ejected by the inner
planets. Furthermore, the interaction can implant giant planets on
moderately-high eccentricities at semimajor axes AU, a region otherwise
hard to populate. Our work supports the hypothesis that most hot Jupiters
reached their current orbits following a phase of high eccentricity, possibly
excited by other planetary or stellar companions.Comment: Replaced with accepted versio
The effects of external planets on inner systems: multiplicities, inclinations, and pathways to eccentric warm Jupiters
We study how close-in systems such as those detected by Kepler are affected
by the dynamics of bodies in the outer system. We consider two scenarios: outer
systems of giant planets potentially unstable to planet--planet scattering, and
wide binaries that may be capable of driving Kozai or other secular variations
of outer planets' eccentricities. Dynamical excitation of planets in the outer
system reduces the multiplicity of Kepler-detectable planets in the inner
system in of our systems. Accounting for the occurrence rates of
wide-orbit planets and binary stars, of close-in systems could be
destabilised by their outer companions in this way. This provides some
contribution to the apparent excess of systems with a single transiting planet
compared to multiple, however, it only contributes at most of the
excess. The effects of the outer dynamics can generate systems similar to
Kepler-56 (two coplanar planets significantly misaligned with the host star)
and Kepler-108 (two significantly non-coplanar planets in a binary). We also
identify three pathways to the formation of eccentric warm Jupiters resulting
from the interaction between outer and inner systems: direct inelastic
collision between an eccentric outer and an inner planet, secular eccentricity
oscillations that may "freeze out" when scattering resolves in the outer
system; and scattering in the inner system followed by "uplift", where inner
planets are removed by interaction with the outer planets. In these scenarios,
the formation of eccentric warm Jupiters is a signature of a past history of
violent dynamics among massive planets beyond au.Comment: 24 pages, 19 figures. Accepted to MNRA
Monte Carlo Predictions of Far-Infrared Emission from Spiral Galaxies
We present simulations of Far Infrared (FIR) emission by dust in spiral
galaxies, based on the Monte Carlo radiative transfer code of Bianchi, Ferrara
& Giovanardi (1996). The radiative transfer is carried out at several
wavelength in the Ultraviolet, optical and Near Infrared, to cover the range of
the stellar Spectral Energy Distribution (SED). Together with the images of the
galactic model, a map of the energy absorbed by dust is produced. Using
Galactic dust properties, the spatial distribution of dust temperature is
derived under the assumption of thermal equilibrium. A correction is applied
for non-equilibrium emission in the Mid Infrared. Images of dust emission can
then be produced at any wavelength in the FIR.
We show the application of the model to the spiral galaxy NGC 6946. The
observed stellar SED is used as input and models are produced for different
star-dust geometries. It is found that only optically thick dust disks can
reproduce the observed amount of FIR radiation. However, it is not possible to
reproduce the large FIR scalelength suggested by recent observation of spirals
at 200 um, even when the scalelength of the dust disk is larger than that for
stars. Optically thin models have ratios of optical/FIR scalelengths closer to
the 200um observations, but with smaller absolute scalelengths than optically
thick cases. The modelled temperature distributions are compatible with
observations of the Galaxy and other spirals. We finally discuss the
approximations of the model and the impact of a clumpy stellar and dust
structure on the FIR simulations.Comment: 19 pages, 6 figures, accepted by A&
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