119 research outputs found
Observational constraints on tidal effects using orbital eccentricities
We have analysed radial velocity measurements for known transiting exoplanets
to study the empirical signature of tidal orbital evolution for close-in
planets. Compared to standard eccentricity determination, our approach is
modified to focus on the rejection of the null hypothesis of a circular orbit.
We are using a MCMC analysis of radial velocity measurements and photometric
constraints, including a component of correlated noise, as well as Bayesian
model selection to check if the data justifies the additional complexity of an
eccentric orbit. We find that among planets with non-zero eccentricity values
quoted in the literature, there is no evidence for an eccentricity detection
for the 7 planets CoRoT-5b, WASP-5b, WASP-6b, WASP-10b, WASP-12b, WASP-17b, and
WASP-18b. In contrast, we confirm the eccentricity of HAT-P-16b,
e=0.034\pm0.003, the smallest eccentricity that is reliably measured so far for
an exoplanet as well as that of WASP-14b, which is the planet at the shortest
period (P=2.24 d), with a confirmed eccentricity, e= 0.088\pm0.003. As part of
the study, we present new radial velocity data using the HARPS spectrograph for
CoRoT-1, CoRoT-3, WASP-2, WASP-4, WASP-5 and WASP-7 as well as the SOPHIE
spectrograph for HAT-P-4, HAT-P-7, TrES-2 and XO-2.
We show that the dissipative effect of tides raised in the planet by the star
and vice-versa explain all the eccentricity and spin-orbit alignment
measurements available for transiting planets. We revisit the mass-period
relation (Mazeh et al. 2005, Pont 2011) and consider its relation to the
stopping mechanism of orbital migration for hot Jupiters. In addition to
CoRoT-2 and HD 189733 (Pont 2009), we find evidence for excess rotation of the
star in the systems CoRoT-18, HAT-P-20, WASP-19 and WASP-43.Comment: 31 pages, 17 figures. Accepted by MNRAS (Feb 2012
Spatial structuring and size selection as collective behaviours in an agent-based model for barchan fields.
International audienceIn order to test parameters of the peculiar dynamics occurring in barchan fields, and compute statistical analysis over large numbers of dunes, we build and study an agent-based model, which includes the well-known physics of an isolated barchan, and observations of interactions between dunes. We showed in a previous study that such a model, where barchans interact through short-range sand recapture and collisions, reproduces the peculiar behaviours of real fields, namely its spatial structuring along the wind direction, and the size selection by the local density. In this paper we focus on the mechanisms that drives these features. In particular, we show that eolian remote sand transfer between dunes ensures that a dense field structures itself into a very heterogeneous pattern, which alternates dense and diluted stripes in the wind direction. In these very dense clusters of dunes, the accumulation of collisions leads to the local emergence of a new size for the dunes
The Earth as an extrasolar transiting planet: Earth's atmospheric composition and thickness revealed by Lunar eclipse observations
An important goal within the quest for detecting an Earth-like extrasolar
planet, will be to identify atmospheric gaseous bio-signatures. Observations of
the light transmitted through the Earth's atmosphere, as for an extrasolar
planet, will be the first step for future comparisons. We have completed
observations of the Earth during a Lunar eclipse, a unique situation similar to
that of a transiting planet. We aim at showing what species could be detected
in its atmosphere at optical wavelengths, where a lot of photons are available
in the masked stellar light. We present observations of the 2008 August 16 Moon
eclipse performed with the SOPHIE spectrograph at the Observatoire de
Haute-Provence. Locating the spectrograph fibers in the penumbra of the
eclipse, the Moon irradiance is then a mix of direct, unabsorbed Sun light and
solar light that has passed through the Earth's limb. This mixture essentially
reproduces what is recorded during the transit of an extrasolar planet. We
report here the clear detection of several Earth atmospheric compounds in the
transmission spectra, such as ozone, molecular oxygen, and neutral sodium as
well as molecular nitrogen and oxygen through the Rayleigh signature. Moreover,
we present a method that allows us to derive the thickness of the atmosphere
versus the wavelength for penumbra eclipse observations. We quantitatively
evaluate the altitude at which the atmosphere becomes transparent for important
species like molecular oxygen and ozone, two species thought to be tightly
linked to the presence of life. The molecular detections presented here are an
encouraging first attempt, necessary to better prepare for the future of
extremely-large telescopes and transiting Earth-like planets. Instruments like
SOPHIE will be mandatory when characterizing the atmospheres of transiting
Earth-like planets from the ground and searching for bio-marker signatures.Comment: 15 pages, 14 figures, 2 tables. Accepted for publication in Astronomy
and Astrophysic
The thermal emission of the exoplanets WASP-1b and WASP-2b
We present a comparative study of the thermal emission of the transiting
exoplanets WASP-1b and WASP-2b using the Spitzer Space Telescope. The two
planets have very similar masses but suffer different levels of irradiation and
are predicted to fall either side of a sharp transition between planets with
and without hot stratospheres. WASP-1b is one of the most highly irradiated
planets studied to date. We measure planet/star contrast ratios in all four of
the IRAC bands for both planets (3.6-8.0um), and our results indicate the
presence of a strong temperature inversion in the atmosphere of WASP-1b,
particularly apparent at 8um, and no inversion in WASP-2b. In both cases the
measured eclipse depths favor models in which incident energy is not
redistributed efficiently from the day side to the night side of the planet. We
fit the Spitzer light curves simultaneously with the best available radial
velocity curves and transit photometry in order to provide updated measurements
of system parameters. We do not find significant eccentricity in the orbit of
either planet, suggesting that the inflated radius of WASP-1b is unlikely to be
the result of tidal heating. Finally, by plotting ratios of secondary eclipse
depths at 8um and 4.5um against irradiation for all available planets, we find
evidence for a sharp transition in the emission spectra of hot Jupiters at an
irradiation level of 2 x 10^9 erg/s/cm^2. We suggest this transition may be due
to the presence of TiO in the upper atmospheres of the most strongly irradiated
hot Jupiters.Comment: 10 pages, submitted to Ap
A giant comet-like cloud of hydrogen escaping the warm Neptune-mass exoplanet GJ 436b
Exoplanets orbiting close to their parent stars could lose some fraction of
their atmospheres because of the extreme irradiation. Atmospheric mass loss
primarily affects low-mass exoplanets, leading to suggest that hot rocky
planets might have begun as Neptune-like, but subsequently lost all of their
atmospheres; however, no confident measurements have hitherto been available.
The signature of this loss could be observed in the ultraviolet spectrum, when
the planet and its escaping atmosphere transit the star, giving rise to deeper
and longer transit signatures than in the optical spectrum. Here we report that
in the ultraviolet the Neptune-mass exoplanet GJ 436b (also known as Gliese
436b) has transit depths of 56.3 +/- 3.5% (1 sigma), far beyond the 0.69%
optical transit depth. The ultraviolet transits repeatedly start ~2 h before,
and end >3 h after the ~1 h optical transit, which is substantially different
from one previous claim (based on an inaccurate ephemeris). We infer from this
that the planet is surrounded and trailed by a large exospheric cloud composed
mainly of hydrogen atoms. We estimate a mass-loss rate in the range of
~10^8-10^9 g/s, which today is far too small to deplete the atmosphere of a
Neptune-like planet in the lifetime of the parent star, but would have been
much greater in the past.Comment: Published in Nature on 25 June 2015. Preprint is 28 pages, 12
figures, 2 table
Updated African biomass burning emission inventories in the framework of the AMMA-IDAF program, with an evaluation of combustion aerosols
African biomass burning emission inventories for gaseous and particulate species have been constructed at a resolution of 1 km by 1km with daily coverage for the 2000–2007 period. These inventories are higher than the GFED2 inventories, which are currently widely in use. Evaluation specifically focusing on combustion aerosol has been carried out with the ORISAM-TM4 global chemistry transport model which includes a detailed aerosol module. This paper compares modeled results with measurements of surface BC concentrations and scattering coefficients from the AMMA Enhanced Observations period, aerosol optical depths and single scattering albedo from AERONET sunphotometers, LIDAR vertical distributions of extinction coefficients as well as satellite data. Aerosol seasonal and interannual evolutions over the 2004–2007 period observed at regional scale and more specifically at the Djougou (Benin) and Banizoumbou (Niger) AMMA/IDAF sites are well reproduced by our global model, indicating that our biomass burning emission inventory appears reasonable
The Compact Linear Collider (CLIC) - 2018 Summary Report
The Compact Linear Collider (CLIC) is a TeV-scale high-luminosity linear collider under development at CERN. Following the CLIC conceptual design published in 2012, this report provides an overview of the CLIC project, its current status, and future developments. It presents the CLIC physics potential and reports on design, technology, and implementation aspects of the accelerator and the detector. CLIC is foreseen to be built and operated in stages, at centre-of-mass energies of 380 GeV, 1.5 TeV and 3 TeV, respectively. CLIC uses a two-beam acceleration scheme, in which 12 GHz accelerating structures are powered via a high-current drive beam. For the first stage, an alternative with X-band klystron powering is also considered. CLIC accelerator optimisation, technical developments and system tests have resulted in an increased energy efficiency (power around 170 MW) for the 380 GeV stage, together with a reduced cost estimate at the level of 6 billion CHF. The detector concept has been refined using improved software tools. Significant progress has been made on detector technology developments for the tracking and calorimetry systems. A wide range of CLIC physics studies has been conducted, both through full detector simulations and parametric studies, together providing a broad overview of the CLIC physics potential. Each of the three energy stages adds cornerstones of the full CLIC physics programme, such as Higgs width and couplings, top-quark properties, Higgs self-coupling, direct searches, and many precision electroweak measurements. The interpretation of the combined results gives crucial and accurate insight into new physics, largely complementary to LHC and HL-LHC. The construction of the first CLIC energy stage could start by 2026. First beams would be available by 2035, marking the beginning of a broad CLIC physics programme spanning 25-30 years
La convention de procédure participative ou l’avenir du contentieux
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