Browse ORBi by ORBi project The Open Access movement
ORBi is a project of

 Publications of Michaël Gillon     Results 1-20 of 364. 1 2 3 4 5 6 7 8 9 10   A search for transiting planets around hot subdwarfs: I. Methods and performance tests on light curves from Kepler, K2, TESS, and CHEOPSVan Grootel, Valérie ; Pozuelos Romero, Francisco José ; Thuillier, Antoine et alin Astronomy and Astrophysics (in press)Context. Hot subdwarfs experienced strong mass loss on the red giant branch (RGB) and are now hot and small He-burning objects. These stars constitute excellent opportunities for addressing the question ... [more ▼]Context. Hot subdwarfs experienced strong mass loss on the red giant branch (RGB) and are now hot and small He-burning objects. These stars constitute excellent opportunities for addressing the question of the evolution of exoplanetary systems directly after the RGB phase of evolution. Aims. In this project we aim to perform a transit survey in all available light curves of hot subdwarfs from space-based telescopes (Kepler, K2, TESS, and CHEOPS) with our custom-made pipeline SHERLOCK in order to determine the occurrence rate of planets around these stars as a function of orbital period and planetary radius. We also aim to determine whether planets that were previously engulfed in the envelope of their red giant host star can survive, even partially, as a planetary remnant. Methods. For this first paper, we performed injection-and-recovery tests of synthetic transits for a selection of representative Kepler, K2, and TESS light curves to determine which transiting bodies in terms of object radius and orbital period we will be able to detect with our tools. We also provide estimates for CHEOPS data, which we analyzed with the pycheops package. Results. Transiting objects with a radius $\lesssim$ 1.0 $R_{\Earth}$ can be detected in most of the Kepler, K2, and CHEOPS targets for the shortest orbital periods (1~d and shorter), reaching values as low as $\sim$0.3 $R_{\Earth}$ in the best cases. Sub-Earth-sized bodies are only reached for the brightest TESS targets and for those that were observed in a significant number of sectors. We also give a series of representative results for larger planets at greater distances, which strongly depend on the target magnitude and on the length and quality of the data. Conclusions. The TESS sample will provide the most important statistics for the global aim of measuring the planet occurrence rate around hot subdwarfs. The Kepler, K2, and CHEOPS data will allow us to search for planetary remnants, that is, very close and small (possibly disintegrating) objects. [less ▲]Detailed reference viewed: 54 (12 ULiège) Discovery of a young low-mass brown dwarf transiting a fast-rotating F-type star by the Galactic Plane eXoplanet (GPX) surveyBenni, P.; Burdanov, A. Y.; Krushinsky, V. V. et alin Monthly Notices of the Royal Astronomical Society (2021), 505We announce the discovery of GPX-1 b, a transiting brown dwarf with a mass of 19.7 ± 1.6 MJup and a radius of 1.47 ± 0.10 RJup, the first substellar object discovered by the Galactic Plane eXoplanet (GPX ... [more ▼]We announce the discovery of GPX-1 b, a transiting brown dwarf with a mass of 19.7 ± 1.6 MJup and a radius of 1.47 ± 0.10 RJup, the first substellar object discovered by the Galactic Plane eXoplanet (GPX) survey. The brown dwarf transits a moderately bright (V = 12.3 mag) fast-rotating F-type star with a projected rotational velocity $v\sin {\, i_*}=40\pm 10$ km s-1. We use the isochrone placement algorithm to characterize the host star, which has effective temperature 7000 ± 200 K, mass 1.68 ± 0.10 $\mathrm{\it M}_\odot$, radius 1.56 ± 0.10 $\mathrm{\it R}_\odot$, and approximate age $0.27_{-0.15}^{+0.09}$ Gyr. GPX-1 b has an orbital period of ~1.75 d and a transit depth of 0.90 ± 0.03 per cent. We describe the GPX transit detection observations, subsequent photometric and speckle-interferometric follow-up observations, and SOPHIE spectroscopic measurements, which allowed us to establish the presence of a substellar object around the host star. GPX-1 was observed at 30-min integrations by TESS in Sector 18, but the data are affected by blending with a 3.4 mag brighter star 42 arcsec away. GPX-1 b is one of about two dozen transiting brown dwarfs known to date, with a mass close to the theoretical brown dwarf/gas giant planet mass transition boundary. Since GPX-1 is a moderately bright and fast-rotating star, it can be followed-up by the means of the Doppler tomography. [less ▲]Detailed reference viewed: 25 (3 ULiège) (6478) Gault: physical characterization of an active main-belt asteroidDevogèle, Maxime; Ferrais, Marin ; Jehin, Emmanuel et alin Monthly Notices of the Royal Astronomical Society (2021), 505In 2018 December, the main-belt asteroid (6478) Gault was reported to display activity. Gault is an asteroid belonging to the Phocaea dynamical family and was not previously known to be active, nor was ... [more ▼]In 2018 December, the main-belt asteroid (6478) Gault was reported to display activity. Gault is an asteroid belonging to the Phocaea dynamical family and was not previously known to be active, nor was any other member of the Phocaea family. In this work, we present the results of photometric and spectroscopic observations that commenced soon after the discovery of activity. We obtained observations over two apparitions to monitor its activity, rotation period, composition, and possible non-gravitational orbital evolution. We find that Gault has a rotation period of P = 2.4929 ± 0.0003 h with a light-curve amplitude of 0.06 magnitude. This short rotation period close to the spin barrier limit is consistent with Gault having a density no smaller than ρ = 1.85 g cm^-3 and its activity being triggered by the YORP (Yarkovsky-O'Keefe-Radzievskii-Paddack) spin-up mechanism. Analysis of the Gault phase curve over phase angles ranging from 0.4° to 23.6° provides an absolute magnitude of H = 14.81 ± 0.04, G1 = 0.25 ± 0.07, and G2 = 0.38 ± 0.04. Model fits to the phase curve find the surface regolith grain size constrained between 100 and 500 $\rm {\mu }$m. Using relations between the phase curve and albedo, we determine that the geometrical albedo of Gault is p[SUB]v[/SUB] = 0.26 ± 0.05 corresponding to an equivalent diameter of $D = 2.8^{+0.4}_{-0.2}$ km. Our spectroscopic observations are all consistent with an ordinary chondrite-like composition (S, or Q-type in the Bus-DeMeo taxonomic classification). A search through archival photographic plate surveys found previously unidentified detections of Gault dating back to 1957 and 1958. Only the latter had been digitized, which we measured to nearly double the observation arc of Gault. Finally, we did not find any signal of activity during the 2020 apparition or non-gravitational effects on its orbit. [less ▲]Detailed reference viewed: 21 (1 ULiège) Warm Jupiters in TESS Full-frame Images: A Catalog and Observed Eccentricity Distribution for Year 1Dong, Jiayin; Huang, Chelsea X.; Dawson, Rebekah I. et alin Astrophysical Journal Supplement Series (2021), 255Warm Jupiters-defined here as planets larger than 6 Earth radii with orbital periods of 8-200 days-are a key missing piece in our understanding of how planetary systems form and evolve. It is currently ... [more ▼]Warm Jupiters-defined here as planets larger than 6 Earth radii with orbital periods of 8-200 days-are a key missing piece in our understanding of how planetary systems form and evolve. It is currently debated whether Warm Jupiters form in situ, undergo disk or high-eccentricity tidal migration, or have a mixture of origin channels. These different classes of origin channels lead to different expectations for Warm Jupiters' properties, which are currently difficult to evaluate due to the small sample size. We take advantage of the Transiting Exoplanet Survey Satellite (TESS) survey and systematically search for Warm Jupiter candidates around main-sequence host stars brighter than the TESS-band magnitude of 12 in the full-frame images in Year 1 of the TESS Prime Mission data. We introduce a catalog of 55 Warm Jupiter candidates, including 19 candidates that were not originally released as TESS objects of interest by the TESS team. We fit their TESS light curves, characterize their eccentricities and transit-timing variations, and prioritize a list for ground-based follow-up and TESS Extended Mission observations. Using hierarchical Bayesian modeling, we find the preliminary eccentricity distributions of our Warm-Jupiter-candidate catalog using a beta distribution, a Rayleigh distribution, and a two-component Gaussian distribution as the functional forms of the eccentricity distribution. Additional follow-up observations will be required to clean the sample of false positives for a full statistical study, derive the orbital solutions to break the eccentricity degeneracy, and provide mass measurements. [less ▲]Detailed reference viewed: 16 (1 ULiège) Transit detection of the long-period volatile-rich super-Earth \nu^2 Lupi d with CHEOPSDelrez, Laetitia ; Ehrenreich, David; Alibert, Yann et alin Nature Astronomy (2021)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 ... [more ▼]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 days via radial velocity monitoring (Udry et al. 2019). The two inner planets (b and c) were recently found to transit (Kane et al. 2020), 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 $2.56\pm0.09$ $R_{\oplus}$ and $8.82\pm0.94$ $M_{\oplus}$, respectively. With its bright Sun-like star, long period, and mild irradiation ($\sim$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 likely 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. [less ▲]Detailed reference viewed: 24 (2 ULiège) A transit timing variation observed for the long-period extremely low-density exoplanet HIP 41378 fBryant, Edward M.; Bayliss, Daniel; Santerne, Alexandre et alin Monthly Notices of the Royal Astronomical Society (2021), 504HIP 41378 f is a temperate 9.2 ± 0.1 R⊕ planet with period of 542.08 d and an extremely low density of 0.09 ± 0.02 g cm-3. It transits the bright star HIP 41378 (V = 8.93), making it an exciting target ... [more ▼]HIP 41378 f is a temperate 9.2 ± 0.1 R⊕ planet with period of 542.08 d and an extremely low density of 0.09 ± 0.02 g cm-3. It transits the bright star HIP 41378 (V = 8.93), making it an exciting target for atmospheric characterization including transmission spectroscopy. HIP 41378 was monitored photometrically between the dates of 2019 November 19 and 28. We detected a transit of HIP 41378 f with NGTS, just the third transit ever detected for this planet, which confirms the orbital period. This is also the first ground-based detection of a transit of HIP 41378 f. Additional ground-based photometry was also obtained and used to constrain the time of the transit. The transit was measured to occur 1.50 h earlier than predicted. We use an analytic transit timing variation (TTV) model to show the observed TTV can be explained by interactions between HIP 41378 e and HIP 41378 f. Using our TTV model, we predict the epochs of future transits of HIP 41378 f, with derived transit centres of TC, 4 = 2459 355.087-0.022+0.031 (2021 May) and TC, 5 = 2459 897.078-0.060+0.114 (2022 November). [less ▲]Detailed reference viewed: 44 (13 ULiège) Six transiting planets and a chain of Laplace resonances in TOI-178Leleu, A.; Alibert, Y.; Hara, N. C. et alin Astronomy and Astrophysics (2021), 649Determining 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 ... [more ▼]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. [less ▲]Detailed reference viewed: 18 (4 ULiège) Massive Search for Spot- and Facula-Crossing Events in 1598 Exoplanetary Transit Light CurvesBaluev, R. V.; Sokov, E. N.; Sokova, I. A. et alin Acta Astronomica (2021), 71We developed a dedicated statistical test for a massive detection of spot- and facula-crossing anomalies in multiple exoplanetary transit light curves, based on the frequentist p-value thresholding. This ... [more ▼]We developed a dedicated statistical test for a massive detection of spot- and facula-crossing anomalies in multiple exoplanetary transit light curves, based on the frequentist p-value thresholding. This test was used to augment our algorithmic pipeline for transit light curves analysis. It was applied to 1598 amateur and professional transit observations of 26 targets being monitored in the EXPANSION project. We detected 109 statistically significant candidate events revealing a roughly 2:1 asymmetry in favor of spots-crossings over faculae-crossings. Although some candidate anomalies likely appear non-physical and originate from systematic errors, such asymmetry between negative and positive events should indicate a physical difference between the frequency of star spots and faculae. Detected spot-crossing events also reveal positive correlation between their amplitude and width, possibly due to spot size correlation. However, the frequency of all detectable crossing events appears just about a few per cent, so they cannot explain excessive transit timing noise observed for several targets. [less ▲]Detailed reference viewed: 23 (3 ULiège) CHEOPS observations of the HD 108236 planetary system: a fifth planet, improved ephemerides, and planetary radiiBonfanti, A.; Delrez, Laetitia ; Hooton, M. J. et alin Astronomy and Astrophysics (2021), 646Context. The detection of a super-Earth and three mini-Neptunes transiting the bright (V = 9.2 mag) star HD 108236 (also known as TOI-1233) was recently reported on the basis of TESS and ground-based ... [more ▼]Context. The detection of a super-Earth and three mini-Neptunes transiting the bright (V = 9.2 mag) star HD 108236 (also known as TOI-1233) was recently reported on the basis of TESS and ground-based light curves.
Aims: We perform a first characterisation of the HD 108236 planetary system through high-precision CHEOPS photometry and improve the transit ephemerides and system parameters.
Methods: We characterise the host star through spectroscopic analysis and derive the radius with the infrared flux method. We constrain the stellar mass and age by combining the results obtained from two sets of stellar evolutionary tracks. We analyse the available TESS light curves and one CHEOPS transit light curve for each known planet in the system.
Results: We find that HD 108236 is a Sun-like star with R[SUB]⋆[/SUB] = 0.877 ± 0.008 R[SUB]⊙[/SUB], M[SUB]⋆[/SUB] = 0.869[SUB]-0.048[/SUB][SUP]+0.050[/SUP] M[SUB]⊙[/SUB], and an age of 6.7[SUB]-5.1[/SUB][SUP]+4.0[/SUP] Gyr. We report the serendipitous detection of an additional planet, HD 108236 f, in one of the CHEOPS light curves. For this planet, the combined analysis of the TESS and CHEOPS light curves leads to a tentative orbital period of about 29.5 days. From the light curve analysis, we obtain radii of 1.615 ± 0.051, 2.071 ± 0.052, 2.539[SUB]-0.065[/SUB][SUP]+0.062[/SUP], 3.083 ± 0.052, and 2.017[SUB]-0.057[/SUB][SUP]+0.052[/SUP] R[SUB]⊕[/SUB] for planets HD 108236 b to HD 108236 f, respectively. These values are in agreement with previous TESS-based estimates, but with an improved precision of about a factor of two. We perform a stability analysis of the system, concluding that the planetary orbits most likely have eccentricities smaller than 0.1. We also employ a planetary atmospheric evolution framework to constrain the masses of the five planets, concluding that HD 108236 b and HD 108236 c should have an Earth-like density, while the outer planets should host a low mean molecular weight envelope.
Conclusions: The detection of the fifth planet makes HD 108236 the third system brighter than V = 10 mag to host more than four transiting planets. The longer time span enables us to significantly improve the orbital ephemerides such that the uncertainty on the transit times will be of the order of minutes for the years to come. A comparison of the results obtained from the TESS and CHEOPS light curves indicates that for a V ~ 9 mag solar-like star and a transit signal of ~500 ppm, one CHEOPS transit light curve ensures the same level of photometric precision as eight TESS transits combined, although this conclusion depends on the length and position of the gaps in the light curve.

Light curves are only available at the CDS via anonymous ftp to http://cdsarc.u-strasbg.fr (ftp://130.79.128.5) or via http://cdsarc.u-strasbg.fr/viz-bin/cat/J/A+A/646/A157 [less ▲]Detailed reference viewed: 94 (2 ULiège) Refining the transit timing and photometric analysis of TRAPPIST-1: Masses, radii, densities, dynamics, and ephemeridesAgol, Eric; Dorn, Caroline; Grimm, Simon L. et alin Planetary Science Journal (2021), 2We have collected transit times for the TRAPPIST-1 system with the Spitzer Space Telescope over four years. We add to these ground-based, HST and K2 transit time measurements, and revisit an N-body ... [more ▼]We have collected transit times for the TRAPPIST-1 system with the Spitzer Space Telescope over four years. We add to these ground-based, HST and K2 transit time measurements, and revisit an N-body dynamical analysis of the seven-planet system using our complete set of times from which we refine the mass ratios of the planets to the star. We next carry out a photodynamical analysis of the Spitzer light curves to derive the density of the host star and the planet densities. We find that all seven planets' densities may be described with a single rocky mass-radius relation which is depleted in iron relative to Earth, with Fe 21 wt% versus 32 wt% for Earth, and otherwise Earth-like in composition. Alternatively, the planets may have an Earth-like composition, but enhanced in light elements, such as a surface water layer or a core-free structure with oxidized iron in the mantle. We measure planet masses to a precision of 3-5%, equivalent to a radial-velocity (RV) precision of 2.5 cm/sec, or two orders of magnitude more precise than current RV capabilities. We find the eccentricities of the planets are very small; the orbits are extremely coplanar; and the system is stable on 10 Myr timescales. We find evidence of infrequent timing outliers which we cannot explain with an eighth planet; we instead account for the outliers using a robust likelihood function. We forecast JWST timing observations, and speculate on possible implications of the planet densities for the formation, migration and evolution of the planet system. [less ▲]Detailed reference viewed: 33 (8 ULiège) Abundance measurements of H[SUB]2[/SUB]O and carbon-bearing species in the atmosphere of WASP-127b confirm its supersolar metallicitySpake, Jessica J.; Sing, David K.; Wakeford, Hannah R. et alin Monthly Notices of the Royal Astronomical Society (2021), 500The chemical abundances of exoplanet atmospheres may provide valuable information about the bulk compositions, formation pathways, and evolutionary histories of planets. Exoplanets with large, relatively ... [more ▼]The chemical abundances of exoplanet atmospheres may provide valuable information about the bulk compositions, formation pathways, and evolutionary histories of planets. Exoplanets with large, relatively cloud-free atmospheres, and which orbit bright stars provide the best opportunities for accurate abundance measurements. For this reason, we measured the transmission spectrum of the bright (V ∼ 10.2), large (1.37 R[SUB]J[/SUB]), sub-Saturn mass (0.19 M[SUB]J[/SUB]) exoplanet WASP-127b across the near-UV to near-infrared wavelength range (0.3-5 μm), using the Hubble and Spitzer Space Telescopes. Our results show a feature-rich transmission spectrum, with absorption from Na, H[SUB]2[/SUB]O, and CO[SUB]2[/SUB], and wavelength-dependent scattering from small-particle condensates. We ran two types of atmospheric retrieval models: one enforcing chemical equilibrium, and the other which fit the abundances freely. Our retrieved abundances at chemical equilibrium for Na, O, and C are all supersolar, with abundances relative to solar values of 9 $^{+15}_{-6}$ , 16 $^{+7}_{-5}$ , and 26 $^{+12}_{-9}$ , respectively. Despite giving conflicting C/O ratios, both retrievals gave supersolar CO[SUB]2[/SUB] volume mixing ratios, which adds to the likelihood that WASP-127b's bulk metallicity is supersolar, since CO[SUB]2[/SUB] abundance is highly sensitive to atmospheric metallicity. We detect water at a significance of 13.7σ. Our detection of Na is in agreement with previous ground-based detections, though we find a much lower abundance, and we also do not find evidence for Li or K despite increased sensitivity. In the future, spectroscopy with James Webb Space Telescope will be able to constrain WASP-127b's C/O ratio, and may reveal the formation history of this metal-enriched, highly observable exoplanet. [less ▲]Detailed reference viewed: 23 (2 ULiège) SPECULOOS: Ultracool dwarf transit survey. Target list and strategySebastian, Daniel ; Gillon, Michaël ; Ducrot, Elsa et alin Astronomy and Astrophysics (2021), 645Context. One of the most promising avenues for the detailed study of temperate Earth-sized exoplanets is the detection of such planets in transit in front of stars that are small and near enough to make ... [more ▼]Context. One of the most promising avenues for the detailed study of temperate Earth-sized exoplanets is the detection of such planets in transit in front of stars that are small and near enough to make it possible to carry out a thorough atmospheric characterisation with next-generation telescopes, such as the James Webb Space telescope (JWST) or Extremely Large Telescope (ELT). In this context, the TRAPPIST-1 planets form a unique benchmark system that has garnered the interest of a large scientific community.
Aims: The SPECULOOS survey is an exoplanet transit survey targeting a volume-limited (40 pc) sample of ultracool dwarf stars (of spectral type M7 and later) that is based on a network of robotic 1 m telescopes especially designed for this survey. The strategy for brighter and earlier targets leverages on the synergy with the ongoing TESS space-based exoplanet transit survey.
Methods: We define the SPECULOOS target list as the sum of three non-overlapping sub-programmes incorporating the latest type objects (T[SUB]eff[/SUB] ≲ 3000 K). Programme 1 features 365 dwarfs that are small and near enough to make it possible to detail atmospheric characterisation of an `Earth-like' planet with the upcoming JWST. Programme 2 features 171 dwarfs of M5-type and later for which a significant detection of a planet similar to TRAPPIST-1b should be within reach of TESS. Programme 3 features 1121 dwarfs that are later than M6-type. These programmes form the basis of our statistical census of short-period planets around ultracool dwarf stars.
Results: Our compound target list includes 1657 photometrically classified late-type dwarfs, with 260 of these targets classified, for the first time, as possible nearby ultracool dwarf stars. Our general observational strategy was to monitor each target between 100 and 200 h with our telescope network, making efficient use of the synergy with TESS for our Programme 2 targets and a proportion of targets in our Programme 1.
Conclusions: Based on Monte Carlo simulations, we expect to detect up to a few dozen temperate, rocky planets. We also expect a number of them to prove amenable for atmospheric characterisation with JWST and other future giant telescopes, which will substantially improve our understanding of the planetary population of the latest-type stars.