arXiv subjects

Magali Deleuil

Publications and source records attributed to Magali Deleuil.

At least 55 records · Page 3Linked to original sources

arXiv2020

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†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.

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arXiv2020

Irradiated ocean planets bridge super-Earth and sub-Neptune populations

Small planets ($\sim$1--3.9 $\Rearth$) constitute more than half of the inventory of the 4000-plus exoplanets discovered so far. Smaller planets are sufficiently dense to be rocky, but those with radii larger than $\sim$1.6 $\Rearth$ are thought to display in many cases hydrogen/helium gaseous envelopes up to $\sim$30\% of the planetary mass. These low-mass planets are highly irradiated and the question of their origin, evolution, and possible links remains open. Here we show that close-in ocean planets affected by greenhouse effect display hydrospheres in supercritical state, which generate inflated atmospheres without invoking the presence of large hydrogen/helium gaseous envelopes. We present a new set of mass-radius relationships for ocean planets with different compositions and different equilibrium temperatures, which are found to be well adapted to low-density sub-Neptune planets. Our model suggests that super-Earths and water-rich sub-Neptunes could belong to the same family of planets, i.e. hydrogen/helium-free planets, with differences between their interiors simply resulting from the variation in the water content.

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arXiv2019

In situ Exploration of the Giant Planets

Remote sensing observations suffer significant limitations when used to study the bulk atmospheric composition of the giant planets of our solar system. This impacts our knowledge of the formation of these planets and the physics of their atmospheres. A remarkable example of the superiority of in situ probe measurements was illustrated by the exploration of Jupiter, where key measurements such as the determination of the noble gases' abundances and the precise measurement of the helium mixing ratio were only made available through in situ measurements by the Galileo probe. Here we describe the main scientific goals to be addressed by the future in situ exploration of Saturn, Uranus, and Neptune, placing the Galileo probe exploration of Jupiter in a broader context. An atmospheric entry probe targeting the 10-bar level would yield insight into two broad themes: i) the formation history of the giant planets and that of the Solar System, and ii) the processes at play in planetary atmospheres. The probe would descend under parachute to measure composition, structure, and dynamics, with data returned to Earth using a Carrier Relay Spacecraft as a relay station. An atmospheric probe could represent a significant ESA contribution to a future NASA New Frontiers or flagship mission to be launched toward Saturn, Uranus, and/or Neptune.

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arXiv2019

CoRoT: The First Space-Based Transit Survey to Explore the Close-in Planet Population

The CoRoT (COnvection, internal ROtation and Transiting planets) space mission was launched in the last days of 2006, becoming the first major space mission dedicated to the search for and study of exoplanets, as well as doing the same for asteroseismological studies of stars. Designed as a small mission, it became highly successful, with, among other things discovering the first planet proved by the measurements of its radius and mass to be definitely "Rocky" or Earth like in its composition and the first close-in brown dwarf with a measured radius. Designed for a lifetime of 3 years it survived in a 900 km orbit around the Earth for 6 years discovering in total 37 planetary systems or brown dwarfs, as well as about one hundred planet candidates and 2269 eclipsing binaires, detached or in contact. In total CoRoT acquired 177 454 light curves, varying in duration from about 30 - 150 days. CoRoT was also a pioneer in the organisation and archiving of such an exoplanetary survey. The development and utilization of this spacecraft has left a legacy of knowledge, both as what concerns the scientific objectives as well as the technical know-how, that is currently being utilized in the construction of the European CHEOPS and PLATO missions.

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arXiv2018

K2 Targets Observed with SPHERE/VLT: An M4-7 Dwarf Companion Resolved around EPIC 206011496

The quest to discover exoplanets is one of the most important missions in astrophysics, and is widely performed using the transit method, which allows for the detection of exoplanets down to the size of Mercury. However, to confirm these detections, additional vetting is mandatory. We selected six K2 targets from campaigns #1 to #8 that show transit light curves corresponding to Earth-sized to Neptune-sized exoplanets. We aim to discard some scenarios that could mimic an exoplanetary transit, leading to a misinterpretation of the data. We performed direct imaging observations using the SPHERE/VLT instrument to probe the close environment of these stars. For five of the K2 targets, we report no detection and we give the detection limits. For EPIC 206011496, we detect a 0.38 $\pm$ 0.06 $M_{\odot}$ companion at a separation of 977.12 $\pm$ 0.73 mas (140.19 $\pm$ 0.11 au). The spectral analysis corresponds to an M4-7 star, and the analysis of the proper motion shows that it is bounded to the primary star. EPIC 206011496 also hosts an Earth-like planetary candidate. If it transits the primary star, its radius is consistent with that of a super-Earth. However, if it transits the companion star, it falls into the mini-Neptune regime.

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arXiv2018

KPS-1b: the first transiting exoplanet discovered using an amateur astronomer's wide-field CCD data

We report the discovery of the transiting hot Jupiter KPS-1b. This exoplanet orbits a V=13.0 K1-type main-sequence star every 1.7 days, has a mass of $1.090_{-0.087}^{+0.086}$ $M_{\mathrm{Jup}}$ and a radius of $1.03_{-0.12}^{+0.13}$ $R_{\mathrm{Jup}}$. The discovery was made by the prototype Kourovka Planet Search (KPS) project, which used wide-field CCD data gathered by an amateur astronomer using readily available and relatively affordable equipment. Here we describe the equipment and observing technique used for the discovery of KPS-1b, its characterization with spectroscopic observations by the SOPHIE spectrograph and with high-precision photometry obtained with 1-m class telescopes. We also outline the KPS project evolution into the Galactic Plane eXoplanet survey (GPX). The discovery of KPS-1b represents a new major step of the contribution of amateur astronomers to the burgeoning field of exoplanetology.

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arXiv2017

The SOPHIE search for northern extrasolar planets - XII. Three giant planets suitable for astrometric mass determination with Gaia

We present new radial velocity measurements for three low-metallicity solar-like stars observed with the SOPHIE spectrograph and its predecessor ELODIE, both installed at the 193 cm telescope of the Haute-Provence Observatory, allowing the detection and characterization of three new giant extrasolar planets in intermediate periods of 1.7 to 3.7 years. All three stars, HD17674, HD42012 and HD29021 present single giant planetary companions with minimum masses between 0.9 and 2.5 MJup. The range of periods and masses of these companions, along with the distance of their host stars, make them good targets to look for astrometric signals over the lifetime of the new astrometry satellite Gaia. We discuss the preliminary astrometric solutions obtained from the first Gaia data release.

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arXiv2016

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).

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arXiv2015

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.

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arXiv2015

One of the closest exoplanet pairs to the 3:2 Mean Motion Resonance: K2-19b \& c

The K2 mission has recently begun to discover new and diverse planetary systems. In December 2014 Campaign 1 data from the mission was released, providing high-precision photometry for ~22000 objects over an 80 day timespan. We searched these data with the aim of detecting further important new objects. Our search through two separate pipelines led to the independent discovery of K2-19b \& c, a two-planet system of Neptune sized objects (4.2 and 7.2 $R_\oplus$), orbiting a K dwarf extremely close to the 3:2 mean motion resonance. The two planets each show transits, sometimes simultaneously due to their proximity to resonance and alignment of conjunctions. We obtain further ground based photometry of the larger planet with the NITES telescope, demonstrating the presence of large transit timing variations (TTVs), and use the observed TTVs to place mass constraints on the transiting objects under the hypothesis that the objects are near but not in resonance. We then statistically validate the planets through the \texttt{PASTIS} tool, independently of the TTV analysis.

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arXiv2015

SOPHIE velocimetry of Kepler transit candidates XVI. Tomographic measurement of the low obliquity of KOI-12b, a warm Jupiter transiting a fast rotator

We present the detection and characterization of the transiting warm Jupiter KOI-12b, first identified with Kepler with an orbital period of 17.86 days. We combine the analysis of Kepler photometry with Doppler spectroscopy and line-profile tomography of time-series spectra obtained with the SOPHIE spectrograph to establish its planetary nature and derive its properties. To derive reliable estimates for the uncertainties on the tomographic model parameters, we devised an empirical method to calculate statistically independent error bars on the time-series spectra. KOI-12b has a radius of 1.43$\pm$0.13$ R_\mathrm{Jup}$ and a 3$σ$ upper mass limit of 10$M_\mathrm{Jup}$. It orbits a fast-rotating star ($v$sin$i_{\star}$ = 60.0$\pm$0.9 km s$^{-1}$) with mass and radius of 1.45$\pm$0.09 $M_\mathrm{Sun}$ and 1.63$\pm$0.15 $R_\mathrm{Sun}$, located at 426$\pm$40 pc from the Earth. Doppler tomography allowed a higher precision on the obliquity to be reached by comparison with the analysis of the Rossiter-McLaughlin radial velocity anomaly, and we found that KOI-12b lies on a prograde, slightly misaligned orbit with a low sky-projected obliquity $λ$ = 12.6$\stackrel{+3.0}{_{-2.9}}^\circ$. The properties of this planetary system, with a 11.4 magnitude host-star, make of KOI-12b a precious target for future atmospheric characterization.

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arXiv2014

Near-infrared Thermal Emission Detections of a number of hot Jupiters and the Systematics of Ground-based Near-infrared Photometry

We present detections of the near-infrared thermal emission of three hot Jupiters and one brown-dwarf using the Wide-field Infrared Camera (WIRCam) on the Canada-France-Hawaii Telescope (CFHT). These include Ks-band secondary eclipse detections of the hot Jupiters WASP-3b and Qatar-1b and the brown dwarf KELT-1b. We also report Y-band, $K_{CONT}$-band, and two new and one reanalyzed Ks-band detections of the thermal emission of the hot Jupiter WASP-12b. We present a new reduction pipeline for CFHT/WIRCam data, which is optimized for high precision photometry. We also describe novel techniques for constraining systematic errors in ground-based near-infrared photometry, so as to return reliable secondary eclipse depths and uncertainties. We discuss the noise properties of our ground-based photometry for wavelengths spanning the near-infrared (the YJHK-bands), for faint and bright-stars, and for the same object on several occasions. For the hot Jupiters WASP-3b and WASP-12b we demonstrate the repeatability of our eclipse depth measurements in the Ks-band; we therefore place stringent limits on the systematics of ground-based, near-infrared photometry, and also rule out violent weather changes in the deep, high pressure atmospheres of these two hot Jupiters at the epochs of our observations.

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arXiv2014

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.

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arXiv2014

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.

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arXiv2013

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.

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arXiv2013

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.

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arXiv2013

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.

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arXiv2013

SOPHIE velocimetry of Kepler transit candidates. VIII. KOI-205 b: a brown-dwarf companion to a K-type dwarf

We report the discovery of a transiting brown dwarf companion to KOI-205, a K0 main-sequence star, in a 11.720125-day period orbit. The transits were detected by the Kepler space telescope, and the reflex motion of the star was measured using radial velocity observations obtained with the SOPHIE spectrograph. The atmospheric parameters of the host stars were determined from the analysis of high-resolution, high signal-to-noise ratio ESPaDOns spectra obtained for this purpose. Together with spectrophotometric measurements recovered from the literature, these spectra indicate that the star is a mildly metallic K0 dwarf with Teff 5237 $\pm$ 60 K. The mass of the companion is 39.9 $\pm$ 1.0 MJup and its radius is 0.81 $\pm$ 0.02 RJup, in agreement with current theoretical predictions. This is the first time a bona fide brown dwarf companion is detected in orbit around a star of this type. The formation and orbital evolution of brown dwarf companions is briefly discussed in the light of this new discovery.

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