176 research outputs found
CoRoT pictures transiting exoplanets
The detection and characterization of exoplanets have made huge progresses
since the first discoveries in the late nineties. In particular, the
independent measurement of the mass and radius of planets, by combining the
transit and radial-velociy techniques, allowed exploring their density and
hence, their internal structure. With CoRoT (2007-2012), the pioneering CNES
space-based mission in this investigation, about thirty new planets were
characterized. CoRoT has enhanced the diversity of giant exoplanets and
discovered the first telluric exoplanet. Following CoRoT, the NASA Kepler
mission has extended our knowledge to small-size planets, multiple systems and
planets orbiting binaries. Exploring these new worlds will continue with the
NASA/TESS (2017) and ESA/PLATO (2024) missions.Comment: in Comptes Rendus de l'Academie des Sciences / Geoscienc
An upper boundary in the mass-metallicity plane of exo-Neptunes
With the progress of detection techniques, the number of low-mass and
small-size exoplanets is increasing rapidly. However their characteristics and
formation mechanisms are not yet fully understood. The metallicity of the host
star is a critical parameter in such processes and can impact the occurence
rate or physical properties of these planets. While a frequency-metallicity
correlation has been found for giant planets, this is still an ongoing debate
for their smaller counterparts. Using the published parameters of a sample of
157 exoplanets lighter than 40 Mearth, we explore the mass-metallicity space of
Neptunes and Super-Earths. We show the existence of a maximal mass that
increases with metallicity, that also depends on the period of these planets.
This seems to favor in situ formation or alternatively a metallicity-driven
migration mechanism. It also suggests that the frequency of Neptunes (between
10 and 40 Mearth) is, like giant planets, correlated with the host star
metallicity, whereas no correlation is found for Super-Earths (<10 Mearth).Comment: Accepted in MNRAS, 11 pages, 5 figure
Interior-atmosphere modelling to assess the observability of rocky planets with JWST
Super-Earths present compositions dominated by refractory materials. However,
there is a degeneracy in their interior structure between a planet with no
atmosphere and a small Fe content, and a planet with a thin atmosphere and a
higher core mass fraction. To break this degeneracy, atmospheric
characterization observations are required. We present a self-consistent
interior-atmosphere model to constrain the volatile mass fraction, surface
pressure, and temperature of rocky planets with water and CO2 atmospheres.
These parameters obtained in our analysis can then be used to predict
observations in emission spectroscopy and photometry with JWST, which can
determine the presence of an atmosphere, and if present, its composition. To
obtain the bolometric emission and Bond albedo for an atmosphere in
radiative-convective equilibrium, we present the k-uncorrelated approximation
for fast computations within our retrieval on planetary mass, radius and host
stellar abundances. For the generation of emission spectra, we use our
k-correlated atmospheric model. An adaptive MCMC is used for an efficient
sampling of the parameter space at low volatile mass fractions. We show how to
use our modelling approach to predict observations with JWST for TRAPPIST-1 c
and 55 Cancri e. TRAPPIST-1 c's most likely scenario is a bare surface,
although the presence of an atmosphere cannot be ruled out. If the emission in
the MIRI F1500 filter is 731 ppm or higher, there would be a water-rich
atmosphere. For fluxes between 730 and 400 ppm, no atmosphere is present, while
low emission fluxes (300 ppm) indicate a CO2-dominated atmosphere. In the case
of 55 Cancri e, a combined spectrum with NIRCam and MIRI LRS may present high
uncertainties at wavelengths between 3 and 3.7 m. However, this does not
affect the identification of H2O and CO2 because they do not present spectral
features in this wavelength range.Comment: 15 pages, 9 figures. Accepted for publication in A&
PASTIS: Bayesian extrasolar planet validation. I. General framework, models, and performance
A large fraction of the smallest transiting planet candidates discovered by
the Kepler and CoRoT space missions cannot be confirmed by a dynamical
measurement of the mass using currently available observing facilities. To
establish their planetary nature, the concept of planet validation has been
advanced. This technique compares the probability of the planetary hypothesis
against that of all reasonably conceivable alternative false-positive (FP)
hypotheses. The candidate is considered as validated if the posterior
probability of the planetary hypothesis is sufficiently larger than the sum of
the probabilities of all FP scenarios. In this paper, we present PASTIS, the
Planet Analysis and Small Transit Investigation Software, a tool designed to
perform a rigorous model comparison of the hypotheses involved in the problem
of planet validation, and to fully exploit the information available in the
candidate light curves. PASTIS self-consistently models the transit light
curves and follow-up observations. Its object-oriented structure offers a large
flexibility for defining the scenarios to be compared. The performance is
explored using artificial transit light curves of planets and FPs with a
realistic error distribution obtained from a Kepler light curve. We find that
data support for the correct hypothesis is strong only when the signal is high
enough (transit signal-to-noise ratio above 50 for the planet case) and remains
inconclusive otherwise. PLATO shall provide transits with high enough
signal-to-noise ratio, but to establish the true nature of the vast majority of
Kepler and CoRoT transit candidates additional data or strong reliance on
hypotheses priors is needed.Comment: Accepted for publication in MNRAS; 23 pages, 11 figure
A small survey of the magnetic fields of planet-host stars
Using spectropolarimetry, we investigate the large-scale magnetic topologies
of stars hosting close-in exoplanets. A small survey of ten stars has been done
with the twin instruments TBL/NARVAL and CFHT/ESPaDOnS between 2006 and 2011.
Each target consists of circular-polarization observations covering 7 to 22
days. For each of the 7 targets in which a magnetic field was detected, we
reconstructed the magnetic field topology using Zeeman-Doppler imaging.
Otherwise, a detection limit has been estimated. Three new epochs of
observations of Tau Boo are presented, which confirm magnetic polarity
reversal. We estimate that the cycle period is 2 years, but recall that a
shorter period of 240 days can not still be ruled out. The result of our survey
is compared to the global picture of stellar magnetic field properties in the
mass-rotation diagram. The comparison shows that these giant planet-host stars
tend to have similar magnetic field topologies to stars without detected
hot-Jupiters. This needs to be confirmed with a larger sample of stars.Comment: Accepted for publication in Monthly Notices of The Royal Astronomical
Societ
A Gas Giant Circumbinary Planet Transiting the F Star Primary of the Eclipsing Binary Star KIC 4862625 and the Independent Discovery and Characterization of the two transiting planets in the Kepler-47 System
We report the discovery of a transiting, gas giant circumbinary planet
orbiting the eclipsing binary KIC 4862625 and describe our independent
discovery of the two transiting planets orbiting Kepler-47 (Orosz et al. 2012).
We describe a simple and semi-automated procedure for identifying individual
transits in light curves and present our follow-up measurements of the two
circumbinary systems. For the KIC 4862625 system, the 0.52+/-0.018 RJup radius
planet revolves every ~138 days and occults the 1.47+/-0.08 MSun, 1.7 +/-0.06
RSun F8 IV primary star producing aperiodic transits of variable durations
commensurate with the configuration of the eclipsing binary star. Our best-fit
model indicates the orbit has a semi-major axis of 0.64 AU and is slightly
eccentric, e=0.1. For the Kepler-47 system, we confirm the results of Orosz et
al. (2012). Modulations in the radial velocity of KIC 4862625A are measured
both spectroscopically and photometrically, i.e. via Doppler boosting, and
produce similar results.Comment: 40 pages, 17 figure
ARCHI: pipeline for light curve extraction of CHEOPS background star
High precision time series photometry from space is being used for a number
of scientific cases. In this context, the recently launched CHEOPS (ESA)
mission promises to bring 20 ppm precision over an exposure time of 6 hours,
when targeting nearby bright stars, having in mind the detailed
characterization of exoplanetary systems through transit measurements. However,
the official CHEOPS (ESA) mission pipeline only provides photometry for the
main target (the central star in the field). In order to explore the potential
of CHEOPS photometry for all stars in the field, in this paper we present
archi, an additional open-source pipeline module{\dag}to analyse the background
stars present in the image. As archi uses the official Data Reduction Pipeline
data as input, it is not meant to be used as independent tool to process raw
CHEOPS data but, instead, to be used as an add-on to the official pipeline. We
test archi using CHEOPS simulated images, and show that photometry of
background stars in CHEOPS images is only slightly degraded (by a factor of 2
to 3) with respect to the main target. This opens a potential for the use of
CHEOPS to produce photometric time series of several close-by targets at once,
as well as to use different stars in the image to calibrate systematic errors.
We also show one clear scientific application where the study of the companion
light curve can be important for the understanding of the contamination on the
main target.Comment: 14 pages, 13 figures, accepted for publication in MNRAS, all code
available at https://github.com/Kamuish/arch
CoRoT: harvest of the exoplanet program
One of the objectives of the CoRoT mission is the search for transiting
extrasolar planets using high-precision photometry, and the accurate
characterization of their fundamental parameters. The CoRoT satellite
consecutively observes crowded stellar fields since February 2007, in
high-cadence precise photometry; periodic eclipses are detected and analysed in
the stellar light curves. Then complementary observations using ground-based
facilities allows establishing the nature of the transiting body and its mass.
CoRoT has acquired more than 163,000 light curves and detected about 500 planet
candidates. A fraction of them (5%) are confirmed planets whose masses are
independently measured. Main highlights of the CoRoT discoveries are: i) the
variety of internal structures in close-in giant planets, ii) the
characterisation of the first known transiting rocky planet, CoRoT-7 b, iii)
multiple constraints on the formation, evolution, role of tides in planetary
systems.Comment: Icarus, in press, special issue on Exoplanet
The Carbon-Rich Gas in the Beta Pictoris Circumstellar Disk
The edge-on disk surrounding the nearby young star Beta Pictoris is the
archetype of the "debris disks", which are composed of dust and gas produced by
collisions and evaporation of planetesimals, analogues of Solar System comets
and asteroids. These disks provide a window on the formation and early
evolution of terrestrial planets. Previous observations of Beta Pic concluded
that the disk gas has roughly solar abundances of elements [1], but this poses
a problem because such gas should be rapidly blown away from the star, contrary
to observations of a stable gas disk in Keplerian rotation [1, 2]. Here we
report the detection of singly and doubly ionized carbon (CII, CIII) and
neutral atomic oxygen (OI) gas in the Beta Pic disk; measurement of these
abundant volatile species permits a much more complete gas inventory. Carbon is
extremely overabundant relative to every other measured element. This appears
to solve the problem of the stable gas disk, since the carbon overabundance
should keep the gas disk in Keplerian rotation [3]. New questions arise,
however, since the overabundance may indicate the gas is produced from material
more carbon-rich than the expected Solar System analogues.Comment: Accepted for publication in Nature. PDF document, 12 pages.
Supplementary information may be found at
http://www.dtm.ciw.edu/akir/Documents/roberge_supp.pdf *** Version 2 :
Removed extraneous publication information, per instructions from the Nature
editor. No other changes mad
Kepler-413b: a slightly misaligned, Neptune-size transiting circumbinary planet
We report the discovery of a transiting, Rp = 4.347+/-0.099REarth,
circumbinary planet (CBP) orbiting the Kepler K+M Eclipsing Binary (EB) system
KIC 12351927 (Kepler-413) every ~66 days on an eccentric orbit with ap =
0.355+/-0.002AU, ep = 0.118+/-0.002. The two stars, with MA =
0.820+/-0.015MSun, RA = 0.776+/-0.009RSun and MB = 0.542+/-0.008MSun, RB =
0.484+/-0.024RSun respectively revolve around each other every
10.11615+/-0.00001 days on a nearly circular (eEB = 0.037+/-0.002) orbit. The
orbital plane of the EB is slightly inclined to the line of sight (iEB =
87.33+/-0.06 degrees) while that of the planet is inclined by ~2.5 degrees to
the binary plane at the reference epoch. Orbital precession with a period of
~11 years causes the inclination of the latter to the sky plane to continuously
change. As a result, the planet often fails to transit the primary star at
inferior conjunction, causing stretches of hundreds of days with no transits
(corresponding to multiple planetary orbital periods). We predict that the next
transit will not occur until 2020. The orbital configuration of the system
places the planet slightly closer to its host stars than the inner edge of the
extended habitable zone. Additionally, the orbital configuration of the system
is such that the CBP may experience Cassini-States dynamics under the influence
of the EB, in which the planet's obliquity precesses with a rate comparable to
its orbital precession. Depending on the angular precession frequency of the
CBP, it could potentially undergo obliquity fluctuations of dozens of degrees
(and complex seasonal cycles) on precession timescales.Comment: 48 pages, 13 figure
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