The Characterising Exoplanet Satellite (CHEOPS) is a space mission designed to perform photometric observations of bright stars to obtain precise radii measurements of transiting planets. The high-precision photometry of CHEOPS relies on careful on-ground calibration of its payload. For that purpose, intensive pre-launch campaigns of measurements were carried out to calibrate the instrument and characterise its photometric performances. We report on main results of these campaigns, provide a complete analysis of data sets and estimate in-flight photometric performance by mean of end-to-end simulation. The on-ground photometric stability of the instrument is found to be of the order of 15 parts per million over 5 hours. Our end-to-end simulation shows that measurements of planet-to-star radii ratio with CHEOPS can be determined with a precision of 2% for a Neptune-size planet transiting a K-dwarf star and 5% for an Earth-size planet orbiting a Sun-like star. It corresponds to signal-to-noise ratios on the transit depths of 25 and 10 respectively, allowing the characterisation and detection of these planets. The pre-launch CHEOPS performances are shown to be compliant with the mission requirements.
The CHaracterising ExOPlanet Satellite (CHEOPS) is a mission dedicated to the search for exoplanetary transits through high precision photometry of bright stars already known to host planets. The telescope will provide the unique capability of determining accurate radii for planets whose masses have already been measured from ground-based spectroscopic surveys. This will allow a first-order characterisation of the planets' internal structure through the determination of the bulk density, providing direct insight into their composition. The CHEOPS simulator has been developed to perform detaile…
The CHaracterizing ExOPlanet Satellite (CHEOPS), to be launched in December 2019, will detect and characterize small size exoplanets via ultra high precision photometry during transits. CHEOPS is designed as a follow-up telescope and therefore it will monitor a single target at a time. The scientific users will retrieve science-ready light curves of the target, automatically generated by the CHEOPS data reduction pipeline of the Science Operations Centre. This paper describes how the pipeline processes the series of raw images and, in particular, how it handles the specificities of CHEOPS data…
CHEOPS(CHaracterising ExOPlanet Satellite) is an ESA S-class mission that observes bright stars at high cadence from low-Earth orbit. The main aim of the mission is to characterize exoplanets that transit nearby stars using ultrahigh precision photometry. Here we report the analysis of transits observed by CHEOPS during its Early Science observing programme for four well-known exoplanets: GJ436b, HD106315b, HD97658b and GJ1132b. The analysis is done using pycheops, an open-source software package we have developed to easily and efficiently analyse CHEOPS light curve data using state-of-the-art…
Characterising transiting exoplanets at long orbital period: lessons learned for PLATO from 10 years of monitoring the HIP41378 system
Univ. Grenoble Alpes（格勒诺布尔阿尔卑斯大学）；CNRS（法国国家科学研究中心）；IPAG（天体物理学与行星学研究所）；Aix Marseille Univ（艾克斯-马赛大学）；CNES（法国国家空间研究中心）；LAM（拉奥朗实验室）；Department of Astronomy, University of Geneva（日内瓦大学天文系）
Recent TESS-based studies have suggested that the dayside of KELT-1b, a strongly-irradiated brown dwarf, is significantly brighter in visible light than what would be expected based on Spitzer observations in infrared. We observe eight eclipses of KELT-1b with CHEOPS (CHaracterising ExOPlanet Satellite) to measure its dayside brightness temperature in the bluest passband observed so far, and model the CHEOPS photometry jointly with the existing optical and NIR photometry from TESS, LBT, CFHT, and Spitzer. Our modelling leads to a self-consistent dayside spectrum for KELT-1b covering the CHEOPS…
The CHaracterising ExOPlanet Satellite (CHEOPS) was selected in 2012, as the first small mission in the ESA Science Programme and successfully launched in December 2019. CHEOPS is a partnership between ESA and Switzerland with important contributions by ten additional ESA Member States. CHEOPS is the first mission dedicated to search for transits of exoplanets using ultrahigh precision photometry on bright stars already known to host planets. As a follow-up mission, CHEOPS is mainly dedicated to improving, whenever possible, existing radii measurements or provide first accurate measurements fo…
Secondary eclipses and phase curves reveal information about the reflectivity and heat distribution in exoplanet atmospheres. The phase curve is composed of a combination of reflected, and thermally emitted light from the planet, and for circular orbits the phase curve peaks during the secondary eclipse or at an orbital phase of 0.5. Physical mechanisms have been discovered which shift the phase curve maximum of tidally locked close in planets to the right, or left, of the secondary eclipse. These mechanisms include cloud formations, and atmospheric superrotation, both of which serve to shift …
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 a…
The power of polarimetry for characterising exoplanet atmospheres, clouds, and surfaces with NASA's Habitable Worlds Observatory
University of Bristol（布里斯托大学）；University of Oxford（牛津大学）；University of Exeter（埃克塞特大学）；The Open University（开放大学）；University of Edinburgh（爱丁堡大学）；Leiden Observatory（莱顿天文台）；Delft University of Technology（代尔夫特理工大学）
Planets emit thermal radiation and reflect incident light that they recieve from their host stars. As a planet orbits it's host star the photometric variations associated with these two effects produce very similar phase curves. If observed through only a single bandpass this leads to a degeneracy between certain planetary parameters that hinder the precise characterization of such planets. However, observing the same planet through two different bandpasses gives one much more information about the planet. Here, we develop a Bayesian methodology for combining photometry from both \emph{Kepler}…
The CHEOPS space mission dedicated to exoplanet follow-up was launched in December 2019, equipped with the capacity to perform photometric measurements at the 20 ppm level. As CHEOPS carries out its observations in a broad optical passband, it can provide insights into the reflected light from exoplanets and constrain the short-wavelength thermal emission for the hottest of planets by observing occultations and phase curves. Here, we report the first CHEOPS observation of an occultation, namely, that of the hot Jupiter WASP-189b, a $M_P \approx 2 M_J$ planet orbiting an A-type star. We detecte…
The ESA Ariel mission has been adopted for launch in 2029 and will conduct a survey of around one thousand exoplanetary atmospheres during its primary mission life. By providing homogeneous datasets, with a high SNR and wide wavelength coverage, Ariel will unveil the atmospheric demographics of these far-away worlds, helping to constrain planet formation and evolution processes on a galactic scale. Ariel seeks to undertake a statistical survey of a diverse population of planets and, therefore, the sample of planets from which this selection can be made is of the utmost importance. While many s…
Discovering and Characterising Exoplanets and Ultracool Dwarfs with the Square Kilometre Array
University of Amsterdam（阿姆斯特丹大学）；ASTRON, The Netherlands Institute for Radio Astronomy（荷兰射电天文研究所）；Observatoire de Paris（巴黎天文台）；National Astronomical Observatory of Japan（日本国立天文台）；University of Tokyo（东京大学）；California Institute of Technology（加州理工学院）；University of Colorado Boulder（科罗拉多大学博尔德分校）；University of Groningen（格罗宁根大学）
Exoplanetary science is among the fastest evolving fields of today's astronomical research. Ground-based planet-hunting surveys alongside dedicated space missions (Kepler, CoRoT) are delivering an ever-increasing number of exoplanets, now numbering at ~690, with ESA's GAIA mission planned to bring this number into the thousands. The next logical step is the characterisation of these worlds: what is their nature? Why are they as they are? The use of the HST and Spitzer Space Telescope to probe the atmospheres of transiting hot, gaseous exoplanets has demonstrated that it is possible with curren…
LOUPE, the Lunar Observatory for Unresolved Polarimetry of the Earth, is a small, robust spectro-polarimeter with a mission to observe the Earth as an exoplanet. Detecting Earth-like planets in stellar habitable zones is one of the key challenges of modern exoplanetary science. Characterising such planets and searching for traces of life requires the direct detection of their signals. LOUPE provides unique spectral flux and polarisation data of sunlight reflected by the Earth, the only planet known to harbor life. This data will be used to test numerical codes to predict signals of Earth-like …
Mass and radius are two fundamental properties for characterising exoplanets, but only for a relatively small fraction of exoplanets are they both available. Mass is often derived from radial velocity measurements, while the radius is almost always measured using the transit method. For a large number of exoplanets, either the radius or the mass is unknown, while the host star has been characterised. Several mass-radius relations that are dependent on the planet's type have been published that often allow us to predict the radius. Our goal is to derive the radius of exoplanets using only obser…
Inaccurate limb-darkening models can be a significant source of error in the analysis of the light curves for transiting exoplanet and eclipsing binary star systems, particularly for high-precision light curves at optical wavelengths. The power-2 limb-darkening law, $I_λ(μ) = 1 - c\left(1-μ^α\right)$, has recently been proposed as a good compromise between complexity and precision in the treatment of limb-darkening. I have used synthetic spectra based on the 3D stellar atmosphere models from the Stagger-grid to compute the limb-darkening for several passbands (UBVRI, CHEOPS, TESS, Kepler, etc.…
SPIRou, a near infrared spectropolarimeter, is a project of new instrument to be mounted at the Canada France Hawaii Telescope in 2017. One of the main objectives of SPIRou is to reach a radial velocity accuracy better than 1 m/s in the YJHK bands. SPIRou will make a cornerstone into the characterization of Earth-like planets, where the exoplanet statistics is very low. This is even more true for planets transiting M dwarfs, since only 3 low-mass planets have been secured so far to transit such stars. We present here all the synergies that SPIRou will provide to and benefit from photometric tr…
Stellar activity causes difficulties in the characterization of transiting exoplanets. Studies have been performed to quantify its impact on infrared interferometry, but not in the visible domain, which however allows reaching better angular resolution and is also the one mostly used for spectroscopic and photometric measurements. We use a standard case to completely analyse the impact of an exoplanet and a spot on interferometric observables and relate it to current instrument capabilities, taking into account realistic achievable precisions. We built a numerical code called COMETS using anal…
The Extrasolar Planet Search with PRIMA project (ESPRI) aims at characterising and detecting extrasolar planets by measuring the host star's reflex motion using the narrow-angle astrometry capability of the PRIMA facility at the Very Large Telescope Interferometer. A first functional demonstration of the astrometric mode was achieved in early 2011. This marked the start of the astrometric commissioning phase with the purpose of characterising the instrument's performance, which ultimately has to be sufficient for exoplanet detection. We show results obtained from the observation of bright visu…
New photometric space missions to detect and characterise transiting exoplanets are focusing on bright stars to obtain high cadence, high signal-to-noise light curves. Since these missions will be sensitive to stellar oscillations and granulation even for dwarf stars, they will be limited by stellar variability. We tested the performance of Gaussian process (GP) regression on the characterisation of transiting planets, and in particular to determine how many components of variability are necessary to describe high cadence, high signal-to-noise light curves expected from CHEOPS and PLATO. We fo…
A transiting planetary system was discovered independently by two groups, under the names WASP-86 (Faedi et al. 2016) and KELT-12 (Stevens et al. 2017). The properties of the system determined in these works were very different, most tellingly a variation of a factor of three in the measured radius of the planet. We suggest that the system be named WASP-86/KELT-12 to better apportion the credit for discovery between the two groups. We analyse the light curve of this system from the Transiting Exoplanet Survey Satellite, which observed it in two sectors, following the Homogeneous Studies approa…
In the past decade, HCI surveys provided new insights about the frequency and properties of substellar companions at separation larger than 5 au. In this context, our study aims to detect and characterise potential exoplanets and brown dwarfs within debris disks, by considering the SHARDDS survey, which gathers 55 Main Sequence stars with known bright debris disk. We rely on the AutoRSM framework to perform an in-depth analysis of the targets, via the computation of detection maps and contrast curves. A clustering approach is used to divide the set of targets in multiple subsets, in order to r…
