Publications of Michaël Gillon
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See detailA search for transiting planets around hot subdwarfs: I. Methods and performance tests on light curves from Kepler, K2, TESS, and CHEOPS
Van Grootel, Valérie ULiege; Pozuelos Romero, Francisco José ULiege; Thuillier, Antoine ULiege et al

in 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 ▲]

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See detailA transit timing variation observed for the long-period extremely low-density exoplanet HIP 41378 f
Bryant, Edward M.; Bayliss, Daniel; Santerne, Alexandre et al

in Monthly Notices of the Royal Astronomical Society (2021), 504

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 ... [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 ▲]

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See detailMassive Search for Spot- and Facula-Crossing Events in 1598 Exoplanetary Transit Light Curves
Baluev, R. V.; Sokov, E. N.; Sokova, I. A. et al

in Acta Astronomica (2021), 71

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 ... [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 ▲]

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See detailCHEOPS observations of the HD 108236 planetary system: a fifth planet, improved ephemerides, and planetary radii
Bonfanti, A.; Delrez, Laetitia ULiege; Hooton, M. J. et al

in Astronomy and Astrophysics (2021), 646

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 ... [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. <BR /> 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. <BR /> 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. <BR /> 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. <BR /> 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. <P />Light curves are only available at the CDS via anonymous ftp to <A href="http://cdsarc.u-strasbg.fr">http://cdsarc.u-strasbg.fr</A> (ftp://130.79.128.5) or via <A href="http://cdsarc.u-strasbg.fr/viz-bin/cat/J/A+A/646/A157">http://cdsarc.u-strasbg.fr/viz-bin/cat/J/A+A/646/A157</A> [less ▲]

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See detailRefining the transit timing and photometric analysis of TRAPPIST-1: Masses, radii, densities, dynamics, and ephemerides
Agol, Eric; Dorn, Caroline; Grimm, Simon L. et al

in Planetary Science Journal (2021), 2

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 ... [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 ▲]

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See detailAbundance measurements of H[SUB]2[/SUB]O and carbon-bearing species in the atmosphere of WASP-127b confirm its supersolar metallicity
Spake, Jessica J.; Sing, David K.; Wakeford, Hannah R. et al

in Monthly Notices of the Royal Astronomical Society (2021), 500

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 ... [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 ▲]

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See detailSPECULOOS: Ultracool dwarf transit survey. Target list and strategy
Sebastian, Daniel ULiege; Gillon, Michaël ULiege; Ducrot, Elsa ULiege et al

in Astronomy and Astrophysics (2021), 645

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 ... [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. <BR /> 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. <BR /> 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. <BR /> 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. <BR /> 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. <P />Catalogue of the sources is only available at the CDS via anonymous ftp to <A href="http://cdsarc.u-strasbg.fr/">http://cdsarc.u-strasbg.fr</A> (ftp://130.79.128.5) or via <A href="http://cdsarc.u-strasbg.fr/viz-bin/cat/J/A+A/645/A100">http://cdsarc.u-strasbg.fr/viz-bin/cat/J/A+A/645/A100</A> [less ▲]

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See detailVetting of 384 TESS Objects of Interest with TRICERATOPS and Statistical Validation of 12 Planet Candidates
Giacalone, Steven; Dressing, Courtney D.; Jensen, Eric L. N. et al

in Astronomical Journal (2021), 161

We present TRICERATOPS, a new Bayesian tool that can be used to vet and validate TESS Objects of Interest (TOIs). We test the tool on 68 TOIs that have been previously confirmed as planets or rejected as ... [more ▼]

We present TRICERATOPS, a new Bayesian tool that can be used to vet and validate TESS Objects of Interest (TOIs). We test the tool on 68 TOIs that have been previously confirmed as planets or rejected as astrophysical false positives. By looking in the false-positive probability (FPP)-nearby false-positive probability (NFPP) plane, we define criteria that TOIs must meet to be classified as validated planets (FPP < 0.015 and NFPP < 10^-3), likely planets (FPP < 0.5 and NFPP < 10^-3), and likely nearby false positives (NFPP > 10^-1). We apply this procedure on 384 unclassified TOIs and statistically validate 12, classify 125 as likely planets, and classify 52 as likely nearby false positives. Of the 12 statistically validated planets, 9 are newly validated. TRICERATOPS is currently the only TESS vetting and validation tool that models transits from nearby contaminant stars in addition to the target star. We therefore encourage use of this tool to prioritize follow-up observations that confirm bona fide planets and identify false positives originating from nearby stars. [less ▲]

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See detailTOI 122b and TOI 237b: Two Small Warm Planets Orbiting Inactive M Dwarfs Found by TESS
Waalkes, William C.; Berta-Thompson, Zachory K.; Collins, Karen A. et al

in Astronomical Journal (2021), 161

We report the discovery and validation of TOI 122b and TOI 237b, two warm planets transiting inactive M dwarfs observed by the Transiting Exoplanet Survey Satellite (TESS). Our analysis shows that TOI ... [more ▼]

We report the discovery and validation of TOI 122b and TOI 237b, two warm planets transiting inactive M dwarfs observed by the Transiting Exoplanet Survey Satellite (TESS). Our analysis shows that TOI 122b has a radius of 2.72 ± 0.18 R[SUB]⊕[/SUB] and receives 8.8 ± 1.0 times Earth's bolometric insolation, and TOI 237b has a radius of 1.44±0.12 R⊕ and receives 3.7 ± 0.5 times Earth's insolation, straddling the 6.7 × Earth insolation that Mercury receives from the Sun. This makes these two of the cooler planets yet discovered by TESS, even on their 5.08 and 5.43 day orbits. Together, they span the small-planet radius valley, providing useful laboratories for exploring volatile evolution around M dwarfs. Their relatively nearby distances (62.23 ± 0.21 pc and 38.11 ± 0.23 pc, respectively) make them potentially feasible targets for future radial velocity follow-up and atmospheric characterization, although such observations may require substantial investments of time on large telescopes. [less ▲]

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See detailThe TRAPPIST-1 JWST Community Initiative
Gillon, Michaël ULiege; Meadows, Victoria; Agol, Eric et al

in Bulletin of the American Astronomical Society (2020), 52(2), 0208

The upcoming launch of the James Webb Space Telescope (JWST) combined with the unique features of the TRAPPIST-1 planetary system should enable the young field of exoplanetology to enter into the realm of ... [more ▼]

The upcoming launch of the James Webb Space Telescope (JWST) combined with the unique features of the TRAPPIST-1 planetary system should enable the young field of exoplanetology to enter into the realm of temperate Earth-sized worlds. Indeed, the proximity of the system (12pc) and the small size (0.12 R) and luminosity (0.05% L) of its host star should make the comparative atmospheric characterization of its seven transiting planets within reach of an ambitious JWST program. Given the limited lifetime of JWST, the ecliptic location of the star that limits its visibility to 100d per year, the large number of observational time required by this study, and the numerous observational and theoretical challenges awaiting it, its full success will critically depend on a large level of coordination between the involved teams and on the support of a large community. In this context, we present here a community initiative aiming to develop a well-defined sequential structure for the study of the system with JWST and to coordinate on every aspect of its preparation and implementation, both on the observational (e.g. study of the instrumental limitations, data analysis techniques, complementary space-based and ground-based observations) and theoretical levels (e.g. model developments and comparison, retrieval techniques, inferences). Depending on the outcome of the first phase of JWST observations of the planets, this initiative could become the seed of a major JWST Legacy Program devoted to the study of TRAPPIST-1. [less ▲]

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See detailDevelopment of the SPECULOOS exoplanet search project
Sebastian, Daniel ULiege; Pedersen, P. P.; Murray, C. A. et al

in Proceedings of SPIE: The International Society for Optical Engineering (2020, December 01), 11445

SPECULOOS (Search for habitable Planets EClipsing ULtra-cOOl Stars) aims to perform a transit search on the nearest (< 40 pc) ultracool (< 3000K) dwarf stars. The project's main motivation is to discover ... [more ▼]

SPECULOOS (Search for habitable Planets EClipsing ULtra-cOOl Stars) aims to perform a transit search on the nearest (< 40 pc) ultracool (< 3000K) dwarf stars. The project's main motivation is to discover potentially habitable planets well-suited for detailed atmospheric characterisation with upcoming giant telescopes, like the James Webb Space Telescope (JWST) and European Large Telescope (ELT). The project is based on a network of 1m robotic telescopes, namely the four ones of the SPECULOOS-Southern Observatory (SSO) in Cerro Paranal, Chile, one telescope of the SPECULOOS-Northern Observatory (SNO) in Tenerife, and the SAINTEx telescope in San Pedro Martir, Mexico. The prototype survey of the SPECULOOS project on the 60 cm TRAPPIST telescope (Chile) discovered the TRAPPIST-1 system, composed of seven temperate Earth-sized planets orbiting a nearby (12 pc) Jupiter-sized star. In this paper, we review the current status of SPECULOOS, its first results, the plans for its development, and its connection to the Transiting Exoplanet Survey Satellite (TESS) and JWST. [less ▲]

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See detailThe CARMENES search for exoplanets around M dwarfs. LP 714-47 b (TOI 442.01): populating the Neptune desert
Dreizler, S.; Crossfield, I. J. M.; Kossakowski, D. et al

in Astronomy and Astrophysics (2020), 644

We report the discovery of a Neptune-like planet (LP 714-47 b, P = 4.05204 d, m[SUB]b[/SUB] = 30.8 ± 1.5M⊕, Rb= 4.7 ± 0.3 R⊕) located in the "hot Neptune desert". Confirmation of the TESS Object of ... [more ▼]

We report the discovery of a Neptune-like planet (LP 714-47 b, P = 4.05204 d, m[SUB]b[/SUB] = 30.8 ± 1.5M⊕, Rb= 4.7 ± 0.3 R⊕) located in the "hot Neptune desert". Confirmation of the TESS Object of Interest (TOI 442.01) was achieved with radial-velocity follow-up using CARMENES, ESPRESSO, HIRES, iSHELL, and PFS, as well as from photometric data using TESS, Spitzer, and ground-based photometry from MuSCAT2, TRAPPIST-South, MONET-South, the George Mason University telescope, the Las Cumbres Observatory Global Telescope network, the El Sauce telescope, the TÜBİTAK National Observatory, the University of Louisville Manner Telescope, and WASP-South. We also present high-spatial resolution adaptive optics imaging with the Gemini Near-Infrared Imager. The low uncertainties in the mass and radius determination place LP 714-47 b among physically well-characterised planets, allowing for a meaningful comparison with planet structure models. The host star LP 714-47 is a slowly rotating early M dwarf (Teff = 3950 ± 51 K) with a mass of 0.59 ± 0.02M☉ and a radius of 0.58 ± 0.02R☉. From long-term photometric monitoring and spectroscopic activity indicators, we determine a stellar rotation period of about 33 d. The stellar activity is also manifested as correlated noise in the radial-velocity data. In the power spectrum of the radial-velocity data, we detect a second signal with a period of 16 days in addition to the four-day signal of the planet. This could be shown to be a harmonic of the stellar rotation period or the signal of a second planet. It may be possible to tell the difference once more TESS data and radial-velocity data are obtained. <P />RV data are only available at the CDS via anonymous ftp to <A href="http://cdsarc.u-strasbg.fr">http://cdsarc.u-strasbg.fr</A> (ftp://130.79.128.5) or via <A href="http://cdsarc.u-strasbg.fr/viz-bin/cat/J/A+A/644/A127">http://cdsarc.u-strasbg.fr/viz-bin/cat/J/A+A/644/A127</A> <P />Based on observations carried out at the Centro Astronómico Hispano Alemán (CAHA) at Calar Alto, operated jointly by the Junta de Andalucía and the Instituto de Astrofísica de Andalucía (CSIC), on observations carried out at the European Southern Observatory under ESO programme 0103.C-0152(A), and data collected with the 6.5 m Magellan Telescopes located at Las Campanas Observatory, Chile. [less ▲]

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See detailThe hot dayside and asymmetric transit of WASP-189b seen by CHEOPS
Lendl, M.; Csizmadia, Sz; Deline, A. et al

in Astronomy and Astrophysics (2020), 643

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 ... [more ▼]

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. [less ▲]

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See detailπ Earth: A 3.14 day Earth-sized Planet from K2's Kitchen Served Warm by the SPECULOOS Team
Niraula, Prajwal; de Wit, Julien; Rackham, Benjamin V. et al

in Astronomical Journal (2020), 160

We report on the discovery of a transiting Earth-sized (0.95R[SUB]⊕[/SUB]) planet around an M3.5 dwarf star at 57 pc, EPIC 249631677. The planet has a period of ∼3.14 days, i.e., ∼π, with an installation ... [more ▼]

We report on the discovery of a transiting Earth-sized (0.95R[SUB]⊕[/SUB]) planet around an M3.5 dwarf star at 57 pc, EPIC 249631677. The planet has a period of ∼3.14 days, i.e., ∼π, with an installation of 7.45 S[SUB]⊕[/SUB]. The detection was made using publicly available data from K2's Campaign 15. We observed three additional transits with SPECULOOS Southern and Northern Observatories, and a stellar spectrum from Keck/HIRES, which allowed us to validate the planetary nature of the signal. The confirmed planet is well suited for comparative terrestrial exoplanetology. While exoplanets transiting ultracool dwarfs present the best opportunity for atmospheric studies of terrestrial exoplanets with the James Webb Space Telescope, those orbiting mid-M dwarfs within 100 pc such as EPIC 249631677b will become increasingly accessible with the next generation of observatories. [less ▲]

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See detailA super-Earth and a sub-Neptune orbiting the bright, quiet M3 dwarf TOI-1266
Demory, B.-O.; Pozuelos Romero, Francisco José ULiege; Gómez Maqueo Chew, Y. et al

in Astronomy and Astrophysics (2020), 642

We report the discovery and characterisation of a super-Earth and a sub-Neptune transiting the bright (K = 8.8), quiet, and nearby (37 pc) M3V dwarf TOI-1266. We validate the planetary nature of TOI-1266 ... [more ▼]

We report the discovery and characterisation of a super-Earth and a sub-Neptune transiting the bright (K = 8.8), quiet, and nearby (37 pc) M3V dwarf TOI-1266. We validate the planetary nature of TOI-1266 b and c using four sectors of TESS photometry and data from the newly-commissioned 1-m SAINT-EX telescope located in San Pedro Mártir (México). We also include additional ground-based follow-up photometry as well as high-resolution spectroscopy and high-angular imaging observations. The inner, larger planet has a radius of R = 2.37[SUB]-0.12[/SUB][SUP]+0.16[/SUP] R[SUB]⊕[/SUB] and an orbital period of 10.9 days. The outer, smaller planet has a radius of R = 1.56[SUB]-0.13[/SUB][SUP]+0.15[/SUP] R[SUB]⊕[/SUB] on an 18.8-day orbit. The data are found to be consistent with circular, co-planar and stable orbits that are weakly influenced by the 2:1 mean motion resonance. Our TTV analysis of the combined dataset enables model-independent constraints on the masses and eccentricities of the planets. We find planetary masses of M[SUB]p[/SUB] = 13.5[SUB]-9.0[/SUB][SUP]+11.0[/SUP] M[SUB]⊕[/SUB] (<36.8 M[SUB]⊕[/SUB] at 2-σ) for TOI-1266 b and 2.2[SUB]-1.5[/SUB][SUP]+2.0[/SUP] M[SUB]⊕[/SUB] (<5.7 M[SUB]⊕[/SUB] at 2-σ) for TOI-1266 c. We find small but non-zero orbital eccentricities of 0.09[SUB]-0.05[/SUB][SUP]+0.06[/SUP] (<0.21 at 2-σ) for TOI-1266 b and 0.04 ± 0.03 (< 0.10 at 2-σ) for TOI-1266 c. The equilibrium temperatures of both planets are of 413 ± 20 and 344 ± 16 K, respectively, assuming a null Bond albedo and uniform heat redistribution from the day-side to the night-side hemisphere. The host brightness and negligible activity combined with the planetary system architecture and favourable planet-to-star radii ratios makes TOI-1266 an exquisite system for a detailed characterisation. [less ▲]

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See detailThe CARMENES search for exoplanets around M dwarfs. Two planets on opposite sides of the radius gap transiting the nearby M dwarf LTT 3780
Nowak, G.; Luque, R.; Parviainen, H. et al

in Astronomy and Astrophysics (2020), 642

We present the discovery and characterisation of two transiting planets observed by the Transiting Exoplanet Survey Satellite (TESS) orbiting the nearby (d[SUB]⋆[/SUB] ≈ 22 pc), bright (J ≈ 9 mag) M3.5 ... [more ▼]

We present the discovery and characterisation of two transiting planets observed by the Transiting Exoplanet Survey Satellite (TESS) orbiting the nearby (d[SUB]⋆[/SUB] ≈ 22 pc), bright (J ≈ 9 mag) M3.5 dwarf LTT 3780 (TOI-732). We confirm both planets and their association with LTT 3780 via ground-based photometry and determine their masses using precise radial velocities measured with the CARMENES spectrograph. Precise stellar parameters determined from CARMENES high-resolution spectra confirm that LTT 3780 is a mid-M dwarf with an effective temperature of T[SUB]eff[/SUB] = 3360 ± 51 K, a surface gravity of log g[SUB]⋆[/SUB] = 4.81 ± 0.04 (cgs), and an iron abundance of [Fe/H] = 0.09 ± 0.16 dex, with an inferred mass of M[SUB]⋆[/SUB] = 0.379 ± 0.016M[SUB]☉[/SUB] and a radius of R[SUB]⋆[/SUB] = 0.382 ± 0.012R[SUB]☉[/SUB]. The ultra-short-period planet LTT 3780 b (P[SUB]b[/SUB] = 0.77 d) with a radius of 1.35[SUB]-0.06[/SUB][SUP]+0.06[/SUP] R[SUB]⊕[/SUB], a mass of 2.34[SUP]-0.23[/SUP][SUB]+0.24[/SUB] M[SUB]⊕[/SUB], and a bulk density of 5.24[SUB]-0.81[/SUB][SUP]+0.94[/SUP] g cm[SUP]-3[/SUP] joins the population of Earth-size planets with rocky, terrestrial composition. The outer planet, LTT 3780 c, with an orbital period of 12.25 d, radius of 2.42[SUB]-0.10[/SUB][SUP]+0.10[/SUP] R[SUB]⊕[/SUB], mass of 6.29[SUB]-0.61[/SUB][SUP]+0.63[/SUP] M[SUB]⊕[/SUB], and mean density of 2.45[SUB]-0.37[/SUB][SUP]+0.44[/SUP] g cm[SUP]-3[/SUP] belongs to the population of dense sub-Neptunes. With the two planets located on opposite sides of the radius gap, this planetary system is anexcellent target for testing planetary formation, evolution, and atmospheric models. In particular, LTT 3780 c is an ideal object for atmospheric studies with the James Webb Space Telescope (JWST). [less ▲]

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See detailGJ 273: On the formation, dynamical evolution and habitability of a planetary system hosted by an M dwarf at 3.75 parsec
Pozuelos Romero, Francisco José ULiege; Suárez, Juan C.; de Elía, Gonzalo C. et al

in Astronomy and Astrophysics (2020), 641(A23), 19

Planets orbiting low-mass stars such as M dwarfs are now considered a cornerstone in the search for life-harbouring planets. GJ273 is a planetary system orbiting an M dwarf only 3.75 pc away, composed of ... [more ▼]

Planets orbiting low-mass stars such as M dwarfs are now considered a cornerstone in the search for life-harbouring planets. GJ273 is a planetary system orbiting an M dwarf only 3.75 pc away, composed of two confirmed planets, GJ273b and GJ273c, and two promising candidates, GJ273d and GJ273e. Planet GJ273b resides in the habitable zone. Currently, due to a lack of observed planetary transits, only the minimum masses of the planets are known.Despite being an interesting system, the GJ273 planetary system is still poorly studied. We aim at precisely determine the physical parameters of the individual planets, in particular to break the mass--inclination degeneracy to accurately determine the mass of the planets. Moreover, we present thorough characterisation of planet GJ273b in terms of its potential habitability. We explored the planetary formation and hydration phases of GJ273 during the first 100 Myr. Then, we analysed the stability of the system. We also searched for regions which may harbour minor bodies such as an asteroid belt and Kuiper belt analogues. We found that the four-planet configuration of the system allows us to break the mass-- inclination degeneracy with the following masses: $2.89\leq M_{\mathrm{b}}\leq3.03\,\mathrm{M}_\oplus$, $1.18\leq M_{\mathrm{c}}\leq1.24\,\mathrm{M}_\oplus$, $10.80\leq M_{\mathrm{d}}\leq11.35\,\mathrm{M}_\oplus$, and $9.30\leq M_{\mathrm{e}}\leq9.70\,\mathrm{M}_\oplus$. That is an Earth-mass planet, a super-Earth and two mini-Neptunes. Moreover, GJ273b is found to be an efficient water captor and GJ273c likely a dry planet. Several stable regions are predicted where minor bodies might reside. We comprehensively discuss the habitability of GJ273b. [less ▲]

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See detailTRAPPIST-1: Global Results of the Spitzer Exploration Science Program Red Worlds
Ducrot, Elsa ULiege; Gillon, Michaël ULiege; Delrez, Laetitia ULiege et al

in Astronomy and Astrophysics (2020), 640(A112), 44

With more than 1000 hours of observation from Feb 2016 to Oct 2019, the Spitzer Exploration Program Red Worlds (ID: 13067, 13175 and 14223) exclusively targeted TRAPPIST-1, a nearby (12pc) ultracool dwarf ... [more ▼]

With more than 1000 hours of observation from Feb 2016 to Oct 2019, the Spitzer Exploration Program Red Worlds (ID: 13067, 13175 and 14223) exclusively targeted TRAPPIST-1, a nearby (12pc) ultracool dwarf star orbited by seven transiting Earth-sized planets, all well-suited for a detailed atmospheric characterization with the upcoming JWST. In this paper, we present the global results of the project. We analyzed 88 new transits and combined them with 100 previously analyzed transits, for a total of 188 transits observed at 3.6 or 4.5 $\mu$m. We also analyzed 29 occultations (secondary eclipses) of planet b and eight occultations of planet c observed at 4.5 $\mu$m to constrain the brightness temperatures of their daysides. We identify several orphan transit-like structures in our Spitzer photometry, but all of them are of low significance. We do not confirm any new transiting planets. We estimate for TRAPPIST-1 transit depth measurements mean noise floors of $\sim$35 and 25 ppm in channels 1 and 2 of Spitzer/IRAC, respectively. most of this noise floor is of instrumental origins and due to the large inter-pixel inhomogeneity of IRAC InSb arrays, and that the much better interpixel homogeneity of JWST instruments should result in noise floors as low as 10ppm, which is low enough to enable the atmospheric characterization of the planets by transit transmission spectroscopy. We construct updated broadband transmission spectra for all seven planets which show consistent transit depths between the two Spitzer channels. We identify and model five distinct high energy flares in the whole dataset, and discuss our results in the context of habitability. Finally, we fail to detect occultation signals of planets b and c at 4.5 $\mu$m, and can only set 3$\sigma$ upper limits on their dayside brightness temperatures (611K for b 586K for c). [less ▲]

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See detailGlobal analysis of the TRAPPIST Ultra-Cool Dwarf Transit Survey
Lienhard, F.; Queloz, D.; Gillon, Michaël ULiege et al

in Monthly Notices of the Royal Astronomical Society (2020), 497(3), 3790

We conducted a global analysis of the TRAPPIST Ultra-Cool Dwarf Transit Survey - a prototype of the SPECULOOS transit search conducted with the TRAPPIST-South robotic telescope in Chile from 2011 to 2017 ... [more ▼]

We conducted a global analysis of the TRAPPIST Ultra-Cool Dwarf Transit Survey - a prototype of the SPECULOOS transit search conducted with the TRAPPIST-South robotic telescope in Chile from 2011 to 2017 - to estimate the occurrence rate of close-in planets such as TRAPPIST-1b orbiting ultra-cool dwarfs. For this purpose, the photometric data of 40 nearby ultra-cool dwarfs were reanalysed in a self-consistent and fully automated manner starting from the raw images. The pipeline developed specifically for this task generates differential light curves, removes non-planetary photometric features and stellar variability, and searches for transits. It identifies the transits of TRAPPIST-1b and TRAPPIST-1c without any human intervention. To test the pipeline and the potential output of similar surveys, we injected planetary transits into the light curves on a star-by-star basis and tested whether the pipeline is able to detect them. The achieved photometric precision enables us to identify Earth-sized planets orbiting ultra-cool dwarfs as validated by the injection tests. Our planet-injection simulation further suggests a lower limit of 10 per cent on the occurrence rate of planets similar to TRAPPIST-1b with a radius between 1 and 1.3 R[SUB]⊕[/SUB] and the orbital period between 1.4 and 1.8 d. [less ▲]

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See detailThree short-period Jupiters from TESS. HIP 65Ab, TOI-157b, and TOI-169b
Nielsen, L. D.; Brahm, R.; Bouchy, F. et al

in Astronomy and Astrophysics (2020), 639

We report the confirmation and mass determination of three hot Jupiters discovered by the Transiting Exoplanet Survey Satellite (TESS) mission: HIP 65Ab (TOI-129, TIC-201248411) is an ultra-short-period ... [more ▼]

We report the confirmation and mass determination of three hot Jupiters discovered by the Transiting Exoplanet Survey Satellite (TESS) mission: HIP 65Ab (TOI-129, TIC-201248411) is an ultra-short-period Jupiter orbiting a bright (V = 11.1 mag) K4-dwarf every 0.98 days. It is a massive 3.213 ± 0.078 M[SUB]J[/SUB] planet in a grazing transit configuration with an impact parameter of b = 1.17[SUB]-0.08[/SUB][SUP]+0.10[/SUP]. As a result the radius is poorly constrained, 2.03[SUB]-0.49[/SUB][SUP]+0.61[/SUP]R[SUB]J[/SUB]. The planet's distance to its host star is less than twice the separation at which it would be destroyed by Roche lobe overflow. It is expected to spiral into HIP 65A on a timescale ranging from 80 Myr to a few gigayears, assuming a reduced tidal dissipation quality factor of Q[SUB]s[/SUB][SUP]'[/SUP] = 10[SUP]7[/SUP] - 10[SUP]9[/SUP]. We performed a full phase-curve analysis of the TESS data and detected both illumination- and ellipsoidal variations as well as Doppler boosting. HIP 65A is part of a binary stellar system, with HIP 65B separated by 269 AU (3.95 arcsec on sky). TOI-157b (TIC 140691463) is a typical hot Jupiter with a mass of 1.18 ± 0.13 M[SUB]J[/SUB] and a radius of 1.29 ± 0.02 R[SUB]J[/SUB]. It has a period of 2.08 days, which corresponds to a separation of just 0.03 AU. This makes TOI-157 an interesting system, as the host star is an evolved G9 sub-giant star (V = 12.7). TOI-169b (TIC 183120439) is a bloated Jupiter orbiting a V = 12.4 G-type star. It has a mass of 0.79 ±0.06 M[SUB]J[/SUB] and a radius of 1.09[SUB]-0.05[/SUB][SUP]+0.08[/SUP]R[SUB]J[/SUB]. Despite having the longest orbital period (P = 2.26 days) of the three planets, TOI-169b receives the most irradiation and is situated on the edge of the Neptune desert. All three host stars are metal rich with [Fe / H] ranging from 0.18 to0.24. [less ▲]

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