Expected performances of the Characterising Exoplanet Satellite (CHEOPS)

Hoyer, S.; Guterman, P.; Demangeon, O.; Sousa, S. G.; Deleuil, M.; Meunier, J.-C.; Benz, W.

doi:10.1051/0004-6361/201936325

Cited by 98 publications

(100 citation statements)

References 18 publications

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“…These data were automatically processed with the latest version of the CHEOPS data reduction pipeline (DRP v12;Hoyer et al 2020). This includes image calibration (bias, gain, nonlinearity, dark current, and flat field) and instrumental and environmental corrections (cosmic rays and smearing trails of field stars and background).…”

Section: Cheopsmentioning

confidence: 99%

Six transiting planets and a chain of Laplace resonances in TOI-178

Leleu

Alibert²,

Hara³

et al. 2021

A&A

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116

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Determining the architecture of multi-planetary systems is one of the cornerstones of understanding planet formation and evolution. Resonant systems are especially important as the fragility of their orbital configuration ensures that no significant scattering or collisional event has taken place since the earliest formation phase when the parent protoplanetary disc was still present. In this context, TOI-178 has been the subject of particular attention since the first TESS observations hinted at the possible presence of a near 2:3:3 resonant chain. Here we report the results of observations from CHEOPS, ESPRESSO, NGTS, and SPECULOOS with the aim of deciphering the peculiar orbital architecture of the system. We show that TOI-178 harbours at least six planets in the super-Earth to mini-Neptune regimes, with radii ranging from 1.152−0.070+0.073 to 2.87−0.13+0.14 Earth radii and periods of 1.91, 3.24, 6.56, 9.96, 15.23, and 20.71 days. All planets but the innermost one form a 2:4:6:9:12 chain of Laplace resonances, and the planetary densities show important variations from planet to planet, jumping from 1.02−0.23+0.28 to 0.177−0.061+0.055 times the Earth’s density between planets c and d. Using Bayesian interior structure retrieval models, we show that the amount of gas in the planets does not vary in a monotonous way, contrary to what one would expect from simple formation and evolution models and unlike other known systems in a chain of Laplace resonances. The brightness of TOI-178 (H = 8.76 mag, J = 9.37 mag, V = 11.95 mag) allows for a precise characterisation of its orbital architecture as well as of the physical nature of the six presently known transiting planets it harbours. The peculiar orbital configuration and the diversity in average density among the planets in the system will enable the study of interior planetary structures and atmospheric evolution, providing important clues on the formation of super-Earths and mini-Neptunes.

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Section: Cheopsmentioning

confidence: 99%

Six transiting planets and a chain of Laplace resonances in TOI-178

Leleu

Alibert²,

Hara³

et al. 2021

A&A

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116

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“…Owing to the extended and irregular shape of CHEOPS' point spread function (PSF) and the fact that the field rotates around the target along the satellite's orbit, nearby stars produce a time-variable flux contamination in the photometric aperture, in phase with the spacecraft's roll angle. As explained in Hoyer et al (2020), the DRP automatically determines the level of such contamination in the target's aperture for each exposure. The contamination is estimated from simulated images (Futyan et al 2020) that are based on the CHEOPS PSF, the roll angle of each image.…”

Section: Observations Data Reduction and Analysismentioning

confidence: 99%

The hot dayside and asymmetric transit of WASP-189 b seen by CHEOPS

Lendl

Csizmadia

Deline

et al. 2020

A&A

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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-189 b, a M P ≈ 2M J planet orbiting an A-type star. We detected the occultation of WASP-189 b at high significance in individual measurements and derived an occultation depth of dF = 87.9 ± 4.3 ppm based on four occultations. We compared these measurements to model predictions and we find that they are consistent with an unreflective atmosphere heated to a temperature of 3435 ± 27 K, when assuming inefficient heat redistribution. Furthermore, we present two transits of WASP-189 b observed by CHEOPS. These transits have an asymmetric shape that we attribute to gravity darkening of the host star caused by its high rotation rate. We used these measurements to refine the planetary parameters, finding a ∼ 25% deeper transit compared to the discovery paper and updating the radius of WASP-189 b to 1.619 ± 0.021R J. We further measured the projected orbital obliquity to be λ = 86.4 +2.9 −4.4 deg, a value that is in good agreement with a previous measurement from spectroscopic observations, and derived a true obliquity of Ψ = 85.4 ± 4.3 deg. Finally, we provide reference values for the photometric precision attained by the CHEOPS satellite: for the V=6.6 mag star, and using a one-hour binning, we obtain a residual RMS between 10 and 17 ppm on the individual light curves, and 5.7 ppm when combining the four visits.

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“…The simulator has two main use cases: firstly, it provides data that can be used as input to facilitate the development and testing of the on-ground data processing chain at the Software Operations Centre (SOC). The processing chain includes the preprocessing of the RAW data received at the Misson Operations Centre (MOC), Quick Look software for fast inspection of the data, and the data reduction processing chain (Hoyer et al 2020). For the purposes of testing the pre-processing chain, unstacked images generated by CHEOPSim are passed through a separate piece of software, the Data Flow Simulator, which executes the on-board software to compress the images into the bitstream format that will be sent to ground from the spacecraft.…”

Section: Overviewmentioning

confidence: 99%

“…3.1. Validation of CHEOPS photometric extraction performance using simulated targets A validation campaign has been carried out for the data reduction software (Hoyer et al 2020), which will be used to calibrate and correct images and to extract light curves from image time series for real data. The validation used simulated image time series generated by CHEOPSim, with the aim of demonstrating that the scientific requirements for the mission are satisfied.…”

Section: Application: Photometric Extraction For Simulated Exoplanet mentioning

confidence: 99%

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Expected performances of the Characterising Exoplanet Satellite (CHEOPS)

Futyan

Fortier

Beck

et al. 2020

A&A

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Context. 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. By identifying transiting exoplanets with high potential for in-depth characterisation, CHEOPS will also provide prime targets for future instruments suited to the spectroscopic characterisation of exoplanetary atmospheres. Aims. The CHEOPS simulator has been developed to perform detailed simulations of the data which is to be received from the CHEOPS satellite. It generates accurately simulated images that can be used to explore design options and to test the on-ground data processing, in particular, the pipeline producing the photometric time series. It is, thus, a critical tool for estimating the photometric performance expected in flight and to guide photometric analysis. It can be used to prepare observations, consolidate the noise budget, and asses the performance of CHEOPS in realistic astrophysical fields that are difficult to reproduce in the laboratory. Methods. The simulator has been implemented as a highly configurable tool called CHEOPSim, with a web-based user interface. Images generated by CHEOPSim take account of many detailed effects, including variations of the incident signal flux and backgrounds, and detailed modelling of the satellite orbit, pointing jitter and telescope optics, as well as the CCD response, noise and readout. Results. The simulator results presented in this paper have been used in the context of validating the data reduction processing chain, in which image time series generated by CHEOPSim were used to generate light curves for simulated planetary transits across real and simulated targets. Independent analysts were successfully able to detect the planets and measure their radii to an accuracy within the science requirements of the mission: for an Earth-sized planet with an orbital period of 50 days orbiting a Sun-like target with magnitude V = 6, the median measured value of the planet to star radius ratio, Rp/Rs, was 0.00923 ± 0.00054(stat) ± 0.00019(syst), compared to a true input value of 0.00916. For a Neptune-sized planet with an orbital period of 13 days orbiting a target with spectral type K5V and magnitude V = 12, the median measured value of Rp/Rs was 0.05038 ± 0.00061(stat) ± 0.00031(syst), compared to a true input value of 0.05.

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Expected performances of the Characterising Exoplanet Satellite (CHEOPS)

Cited by 98 publications

References 18 publications

Six transiting planets and a chain of Laplace resonances in TOI-178

Six transiting planets and a chain of Laplace resonances in TOI-178

The hot dayside and asymmetric transit of WASP-189 b seen by CHEOPS

Expected performances of the Characterising Exoplanet Satellite (CHEOPS)

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