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Publications (5 of 5) Show all publications
Borsato, L., Piotto, G., Gandolfi, D., Nascimbeni, V., Lacedelli, G., Marzari, F., . . . Walton, N. (2021). Exploiting timing capabilities of the CHEOPS mission with warm-Jupiter planets. Monthly notices of the Royal Astronomical Society, 506(3), 3810-3830
Open this publication in new window or tab >>Exploiting timing capabilities of the CHEOPS mission with warm-Jupiter planets
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2021 (English)In: Monthly notices of the Royal Astronomical Society, ISSN 0035-8711, E-ISSN 1365-2966, Vol. 506, no 3, p. 3810-3830Article in journal (Refereed) Published
Abstract [en]

We present 17 transit light curves of seven known warm-Jupiters observed with the CHaracterising ExOPlanet Satellite (CHEOPS). The light curves have been collected as part of the CHEOPS Guaranteed Time Observation (GTO) program that searches for transit-timing variation (TTV) of warm-Jupiters induced by a possible external perturber to shed light on the evolution path of such planetary systems. We describe the CHEOPS observation process, from the planning to the data analysis. In this work, we focused on the timing performance of CHEOPS, the impact of the sampling of the transit phases, and the improvement we can obtain by combining multiple transits together. We reached the highest precision on the transit time of about 13–16 s for the brightest target (WASP-38, G = 9.2) in our sample. From the combined analysis of multiple transits of fainter targets with G ≥ 11, we obtained a timing precision of ∼2 min. Additional observations with CHEOPS, covering a longer temporal baseline, will further improve the precision on the transit times and will allow us to detect possible TTV signals induced by an external perturber.

Keywords
techniques: photometric, planets and satellites: individual: HAT-P-17 b, KELT-6 b, WASP-8 b, WASP-38 b, WASP-106 b, WASP-130 b, K2-287 b
National Category
Physical Sciences
Identifiers
urn:nbn:se:su:diva-198304 (URN)10.1093/mnras/stab1782 (DOI)000685245200051 ()
Available from: 2021-11-08 Created: 2021-11-08 Last updated: 2022-02-25Bibliographically approved
Leleu, A., Alibert, Y., Hara, N. C., Hooton, M. J., Wilson, T. G., Robutel, P., . . . Wolter, D. (2021). Six transiting planets and a chain of Laplace resonances in TOI-178. Astronomy and Astrophysics, 649, Article ID A26.
Open this publication in new window or tab >>Six transiting planets and a chain of Laplace resonances in TOI-178
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2021 (English)In: Astronomy and Astrophysics, ISSN 0004-6361, E-ISSN 1432-0746, Vol. 649, article id A26Article in journal (Refereed) Published
Abstract [en]

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)</textual-form> 1.152-0.070+0.073 to 2.87(-0.13)(+0.14)</textual-form> 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)</textual-form> 1.02-0.23+0.28 to 0.177(-0.061)(+0.055)</textual-form> 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.

Keywords
techniques: photometric, techniques: spectroscopic, celestial mechanics, planets and satellites: detection, planets and satellites: dynamical evolution and stability
National Category
Physical Sciences
Identifiers
urn:nbn:se:su:diva-195185 (URN)10.1051/0004-6361/202039767 (DOI)000655036600001 ()
Available from: 2021-08-10 Created: 2021-08-10 Last updated: 2022-03-23Bibliographically approved
Benz, W., Broeg, C., Fortier, A., Rando, N., Beck, T., Beck, M., . . . Wolter, D. (2021). The CHEOPS mission. Experimental astronomy, 51, 109-151
Open this publication in new window or tab >>The CHEOPS mission
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2021 (English)In: Experimental astronomy, ISSN 0922-6435, E-ISSN 1572-9508, Vol. 51, p. 109-151Article in journal (Refereed) Published
Abstract [en]

The CHaracterising ExOPlanet Satellite (CHEOPS) was selected on October 19, 2012, as the first small mission (S-mission) in the ESA Science Programme and successfully launched on December 18, 2019, as a secondary passenger on a Soyuz-Fregat rocket from Kourou, French Guiana. 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 for a subset of those planets for which the mass has already been estimated from ground-based spectroscopic surveys. The expected photometric precision will also allow CHEOPS to go beyond measuring only transits and to follow phase curves or to search for exo-moons, for example. Finally, by unveiling 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. To reach its science objectives, requirements on the photometric precision and stability have been derived for stars with magnitudes ranging from 6 to 12 in the V band. In particular, CHEOPS shall be able to detect Earth-size planets transiting G5 dwarf stars (stellar radius of 0.9R(circle dot)) in the magnitude range 6 <= V <= 9 by achieving a photometric precision of 20 ppm in 6 hours of integration time. In the case of K-type stars (stellar radius of 0.7R(circle dot)) of magnitude in the range 9 <= V <= 12, CHEOPS shall be able to detect transiting Neptune-size planets achieving a photometric precision of 85 ppm in 3 hours of integration time. This precision has to be maintained over continuous periods of observation for up to 48 hours. This precision and stability will be achieved by using a single, frame-transfer, back-illuminated CCD detector at the focal plane assembly of a 33.5 cm diameter, on-axis Ritchey-Chretien telescope. The nearly 275 kg spacecraft is nadir-locked, with a pointing accuracy of about 1 arcsec rms, and will allow for at least 1 Gbit/day downlink. The sun-synchronous dusk-dawn orbit at 700 km altitude enables having the Sun permanently on the backside of the spacecraft thus minimising Earth stray light. A mission duration of 3.5 years in orbit is foreseen to enable the execution of the science programme. During this period, 20% of the observing time is available to the wider community through yearly ESA call for proposals, as well as through discretionary time approved by ESA's Director of Science. At the time of this writing, CHEOPS commissioning has been completed and CHEOPS has been shown to fulfill all its requirements. The mission has now started the execution of its science programme.

Keywords
Exoplanets, CHEOPS, Small mission, High-precision transit photometry
National Category
Physical Sciences
Identifiers
urn:nbn:se:su:diva-188153 (URN)10.1007/s10686-020-09679-4 (DOI)000587111800001 ()
Available from: 2021-01-04 Created: 2021-01-04 Last updated: 2024-01-17Bibliographically approved
Delrez, L., Ehrenreich, D., Alibert, Y., Bonfanti, A., Borsato, L., Fossati, L., . . . Walton, N. A. (2021). Transit detection of the long-period volatile-rich super-Earth nu(2) Lupi d with CHEOPS. Nature Astronomy (5), 775-787
Open this publication in new window or tab >>Transit detection of the long-period volatile-rich super-Earth nu(2) Lupi d with CHEOPS
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2021 (English)In: Nature Astronomy, E-ISSN 2397-3366, no 5, p. 775-787Article in journal (Refereed) Published
Abstract [en]

Exoplanets transiting bright nearby stars are key objects for advancing our knowledge of planetary formation and evolution. The wealth of photons from the host star gives detailed access to the atmospheric, interior and orbital properties of the planetary companions. nu(2) Lupi (HD 136352) is a naked-eye (V = 5.78) Sun-like star that was discovered to host three low-mass planets with orbital periods of 11.6, 27.6 and 107.6 d via radial-velocity monitoring(1). The two inner planets (b and c) were recently found to transit(2), prompting a photometric follow-up by the brand new Characterising Exoplanets Satellite (CHEOPS). Here, we report that the outer planet d is also transiting, and measure its radius and mass to be 2.56 +/- 0.09 R-circle plus and 8.82 +/- 0.94 M-circle plus, respectively. With its bright Sun-like star, long period and mild irradiation (similar to 5.7 times the irradiation of Earth), nu(2) Lupi d unlocks a completely new region in the parameter space of exoplanets amenable to detailed characterization. We refine the properties of all three planets: planet b probably has a rocky mostly dry composition, while planets c and d seem to have retained small hydrogen-helium envelopes and a possibly large water fraction. This diversity of planetary compositions makes the nu(2) Lupi system an excellent laboratory for testing formation and evolution models of low-mass planets.

National Category
Physical Sciences
Identifiers
urn:nbn:se:su:diva-196166 (URN)10.1038/s41550-021-01381-5 (DOI)000667639700004 ()
Available from: 2021-09-07 Created: 2021-09-07 Last updated: 2022-02-25Bibliographically approved
Lendl, M., Csizmadia, S., Deline, A., Fossati, L., Kitzmann, D., Heng, K., . . . Wolter, D. (2020). The hot dayside and asymmetric transit of WASP-189 b seen by CHEOPS. Astronomy and Astrophysics, 643, Article ID A94.
Open this publication in new window or tab >>The hot dayside and asymmetric transit of WASP-189 b seen by CHEOPS
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2020 (English)In: Astronomy and Astrophysics, ISSN 0004-6361, E-ISSN 1432-0746, Vol. 643, article id A94Article in journal (Refereed) Published
Abstract [en]

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 MP ≈ 2MJ 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 ± 0.021RJ. We further measured the projected orbital obliquity to be λ = 86.4−4.4+2.9°, 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°. Finally, we provide reference values for the photometric precision attained by the CHEOPS satellite: for the V = 6.6 mag star, and using a 1-h 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.

Keywords
techniques: photometric, planets and satellites: atmospheres, planets and satellites: individual: WASP-189 b
National Category
Physical Sciences
Identifiers
urn:nbn:se:su:diva-188743 (URN)10.1051/0004-6361/202038677 (DOI)000591851400001 ()
Available from: 2021-01-18 Created: 2021-01-18 Last updated: 2022-02-25Bibliographically approved
Identifiers
ORCID iD: ORCID iD iconorcid.org/0000-0002-8863-7828

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