3,576 research outputs found
Les évolutions comparées des prix à la consommation dans les DOM et en métropole.
Les départements français d’outre-mer (DOM) présentent, par rapport à leurs homologues métropolitains, un certain nombre de caractéristiques susceptibles d’introduire des écarts de niveau et d’évolution de prix avec la métropole. Est-ce le cas ?inflation, départements d’outre-mer, conjoncture outre-mer.
An accurate distance to 2M1207Ab
In April 2004 the first image was obtained of a planetary mass companion (now
known as 2M1207 b) in orbit around a self-luminous object different from our
own Sun (the young brown dwarf 2MASSW J1207334-393254, hereafter 2M1207 A).
2M1207 b probably formed via fragmentation and gravitational collapse, offering
proof that such a mechanism can form bodies in the planetary mass regime.
However, the predicted mass, luminosity, and radius of 2M1207 b depend on its
age, distance, and other observables such as effective temperature. To refine
our knowledge of the physical properties of 2M1207 b and its nature, we
obtained an accurate determination of the distance to the 2M1207 A and b system
by measurements of its trigonometric parallax at the milliarcsec level. With
the ESO NTT/SUSI2 telescope, in 2006 we began a campaign of photometric and
astrometric observations to measure the trigonometric parallax of 2M1207 A. An
accurate distance ( pc) to 2M1207A was measured. From distance and
proper motions we derived spatial velocities fully compatible with TWA
membership. With this new distance estimate, we discuss three scenarios
regarding the nature of 2M1207 b: (1) a cool ( K) companion of mass
M, (2) a warmer ( K) and heavier (
M) companion occulted by an edge-on circum-secondary disk or (3) a
hot protoplanet collision afterglow.Comment: 5 pages, 3 figures, accepted for publication as letter in A&A,
6/11/200
Fully Analyzing an Algebraic Polya Urn Model
This paper introduces and analyzes a particular class of Polya urns: balls
are of two colors, can only be added (the urns are said to be additive) and at
every step the same constant number of balls is added, thus only the color
compositions varies (the urns are said to be balanced). These properties make
this class of urns ideally suited for analysis from an "analytic combinatorics"
point-of-view, following in the footsteps of Flajolet-Dumas-Puyhaubert, 2006.
Through an algebraic generating function to which we apply a multiple
coalescing saddle-point method, we are able to give precise asymptotic results
for the probability distribution of the composition of the urn, as well as
local limit law and large deviation bounds.Comment: LATIN 2012, Arequipa : Peru (2012
Spectroscopy across the brown dwarf/planetary mass boundary - I. Near-infrared JHK spectra
With a uniform VLT SINFONI data set of nine targets, we have developed an
empirical grid of J,H,K spectra of the atmospheres of objects estimated to have
very low substellar masses of \sim5-20 MJup and young ages of \sim1-50 Myr.
Most of the targets are companions, objects which are especially valuable for
comparison with atmosphere and evolutionary models, as they present rare cases
in which the age is accurately known from the primary. Based on the sample
youth, all objects are expected to have low surface gravity, and this study
investigates the critical early phases of the evolution of substellar objects.
The spectra are compared with grids of five different theoretical atmosphere
models. This analysis represents the first systematic model comparison with
infrared spectra of young brown dwarfs. The fits to the full JHK spectra of
each object result in a range of best fit effective temperatures of +/-150-300K
whether or not the full model grid or a subset restricted to lower log(g)
values is used. This effective temperature range is significantly larger than
the uncertainty typically assigned when using a single model grid. Fits to a
single wavelength band can vary by up to 1000K using the different models.
Since the overall shape of these spectra is governed more by the temperature
than surface gravity, unconstrained model fits did not find matches with low
surface gravity or a trend in log(g) with age. This suggests that empirical
comparison with spectra of unambiguously young objects targets (such as these
SINFONI data) may be the most reliable method to search for indications of low
surface gravity and youth. For two targets, the SINFONI data are a second epoch
and the data show no variations in morphology over time. The analysis of two
other targets, AB Pic B and CT Cha B, suggests that these objects may have
lower temperatures, and consequently lower masses, than previously estimated.Comment: 15 pages, 13 figure
The multiplicity of exoplanet host stars - New low-mass stellar companions of the exoplanet host stars HD125612 and HD212301
Aims: We present new results from our ongoing multiplicity study of exoplanet
host stars, carried out with SofI/NTT. We provide the most recent list of
confirmed binary and triple star systems that harbor exoplanets.
Methods: We use direct imaging to identify wide stellar and substellar
companions as co-moving objects to the observed exoplanet host stars, whose
masses and spectral types are determined with follow-up photometry and
spectroscopy.
Results: We found two new co-moving companions of the exoplanet host stars
HD125612 and HD212301. HD125612B is a wide M4 dwarf (0.18 Msun) companion of
the exoplanet host star HD125612, located about 1.5 arcmin (~4750 AU of
projected separation) south-east of its primary. In contrast, HD212301B is a
close M3 dwarf (0.35 Msun), which is found about 4.4 arcsec (~230 AU of
projected separation) north-west of its primary.
Conclusions: The binaries HD125612AB and HD212301AB are new members in the
continuously growing list of exoplanet host star systems of which 43 are
presently known. Hence, the multiplicity rate of exoplanet host stars is about
17%.
Based on observations obtained on La Silla in ESO programs 079.C-0099(A),
080.C-0312(A)Comment: 7 pages, 7 figures, 2 tables, A&A in pres
Direct imaging constraints on planet populations detected by microlensing
Results from gravitational microlensing suggested the existence of a large
population of free-floating planetary mass objects. The main conclusion from
this work was partly based on constraints from a direct imaging survey. This
survey determined upper limits for the frequency of stars that harbor giant
exoplanets at large orbital separations. Aims. We want to verify to what extent
upper limits from direct imaging do indeed constrain the microlensing results.
We examine the current derivation of the upper limits used in the microlensing
study and re-analyze the data from the corresponding imaging survey. We focus
on the mass and semi-major axis ranges that are most relevant in context of the
microlensing results. We also consider new results from a recent M-dwarf
imaging survey as these objects are typically the host stars for planets
detected by microlensing. We find that the upper limits currently applied in
context of the microlensing results are probably underestimated. This means
that a larger fraction of stars than assumed may harbor gas giant planets at
larger orbital separations. Also, the way the upper limit is currently used to
estimate the fraction of free-floating objects is not strictly correct. If the
planetary surface density of giant planets around M-dwarfs is described as
df_Planet ~ a^beta da, we find that beta ~ 0.5 - 0.6 is consistent with results
from different observational studies probing semi-major axes between ~0.03 - 30
AU. Having a higher upper limit on the fraction of stars that may have gas
giant planets at orbital separations probed by the microlensing data implies
that more of the planets detected in the microlensing study are potentially
bound to stars rather than free-floating. The current observational data are
consistent with a rising planetary surface density for giant exoplanets around
M-dwarfs out to ~30 AU.Comment: Accepted for publication in A&A as Research Note, 3 page
Phase transitions in soft-committee machines
Equilibrium statistical physics is applied to layered neural networks with
differentiable activation functions. A first analysis of off-line learning in
soft-committee machines with a finite number (K) of hidden units learning a
perfectly matching rule is performed. Our results are exact in the limit of
high training temperatures. For K=2 we find a second order phase transition
from unspecialized to specialized student configurations at a critical size P
of the training set, whereas for K > 2 the transition is first order. Monte
Carlo simulations indicate that our results are also valid for moderately low
temperatures qualitatively. The limit K to infinity can be performed
analytically, the transition occurs after presenting on the order of N K
examples. However, an unspecialized metastable state persists up to P= O (N
K^2).Comment: 8 pages, 4 figure
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