Publications of Michaël Gillon
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See detailPROSE: a PYTHON framework for modular astronomical images processing
Garcia, Lionel ULiege; Timmermans, Mathilde ULiege; Pozuelos, Francisco J. et al

in Monthly Notices of the Royal Astronomical Society (2022), 509

To reduce and analyse astronomical images, astronomers can rely on a wide range of libraries providing low-level implementations of legacy algorithms. However, combining these routines into robust and ... [more ▼]

To reduce and analyse astronomical images, astronomers can rely on a wide range of libraries providing low-level implementations of legacy algorithms. However, combining these routines into robust and functional pipelines requires a major effort that often ends up in instrument-specific and poorly maintainable tools, yielding products that suffer from a low level of reproducibility and portability. In this context, we present PROSE, a PYTHON framework to build modular and maintainable image processing pipelines. Built for astronomy, it is instrument-agnostic and allows the construction of pipelines using a wide range of building blocks, pre-implemented or user-defined. With this architecture, our package provides basic tools to deal with common tasks, such as automatic reduction and photometric extraction. To demonstrate its potential, we use its default photometric pipeline to process 26 TESS candidates follow-up observations and compare their products to the ones obtained with ASTROIMAGEJ, the reference software for such endeavours. We show that PROSE produces light curves with lower white and red noise while requiring less user interactions and offering richer functionalities for reporting. [less ▲]

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See detailAn upper limit on late accretion and water delivery in the TRAPPIST-1 exoplanet system
Raymond, Sean N.; Izidoro, Andre; Bolmont, Emeline et al

in Nature Astronomy (2021)

The TRAPPIST-1 system contains seven roughly Earth-sized planets locked in a multiresonant orbital configuration[SUP]1,2[/SUP], which has enabled precise measurements of the planets' masses and ... [more ▼]

The TRAPPIST-1 system contains seven roughly Earth-sized planets locked in a multiresonant orbital configuration[SUP]1,2[/SUP], which has enabled precise measurements of the planets' masses and constrained their compositions[SUP]3[/SUP]. Here we use the system's fragile orbital structure to place robust upper limits on the planets' bombardment histories. We use N-body simulations to show how perturbations from additional objects can break the multiresonant configuration by either triggering dynamical instability or simply removing the planets from resonance. The planets cannot have interacted with more than ~5% of one Earth mass (M[SUB]⊕[/SUB]) in planetesimals—or a single rogue planet more massive than Earth's Moon—without disrupting their resonant orbital structure. This implies an upper limit of 10[SUP]−4[/SUP]M[SUB]⊕[/SUB] to 10[SUP]−2[/SUP] M[SUB]⊕[/SUB] of late accretion on each planet since the dispersal of the system's gaseous disk. This is comparable to (or less than) the late accretion on Earth after the Moon-forming impact[SUP]4,5[/SUP], and demonstrates that the growth of the TRAPPIST-1 planets was complete in just a few million years, roughly an order of magnitude faster than that of the Earth[SUP]6,7[/SUP]. Our results imply that any large water reservoirs on the TRAPPIST-1 planets must have been incorporated during their formation in the gaseous disk. [less ▲]

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See detailTransit Timings Variations in the three-planet system: TOI-270
Kaye, Laurel; Vissapragada, Shreyas; Günther, Maximilian N. et al

in Monthly Notices of the Royal Astronomical Society (2021)

We present ground and space-based photometric observations of TOI-270 (L231-32), a system of three transiting planets consisting of one super-Earth and two sub-Neptunes discovered by TESS around a bright ... [more ▼]

We present ground and space-based photometric observations of TOI-270 (L231-32), a system of three transiting planets consisting of one super-Earth and two sub-Neptunes discovered by TESS around a bright (K-mag=8.25) M3V dwarf. The planets orbit near low-order mean-motion resonances (5:3 and 2:1), and are thus expected to exhibit large transit timing variations (TTVs). Following an extensive observing campaign using 8 different observatories between 2018 and 2020, we now report a clear detection of TTVs for planets c and d, with amplitudes of ~10 minutes and a super-period of ~3 years, as well as significantly refined estimates of the radii and mean orbital periods of all three planets. Dynamical modeling of the TTVs alone puts strong constraints on the mass ratio of planets c and d and on their eccentricities. When incorporating recently published constraints from radial velocity observations, we obtain masses of $M_{\mathrm{b}}=1.48\pm 0.18\, M_{\oplus}$, $M_{\mathrm{c}}=6.20\pm 0.31\, M_{\oplus}$ and $M_{\mathrm{d}}=4.20\pm 0.16\, M_{\oplus}$ for planets b, c and d, respectively. We also detect small, but significant eccentricities for all three planets : e[SUB]b[/SUB] = 0.0167 ± 0.0084, e[SUB]c[/SUB] = 0.0044 ± 0.0006 and e[SUB]d[/SUB] = 0.0066 ± 0.0020. Our findings imply an Earth-like rocky composition for the inner planet, and Earth-like cores with an additional He/H[SUB]2[/SUB]O atmosphere for the outer two. TOI-270 is now one of the best-constrained systems of small transiting planets, and it remains an excellent target for atmospheric characterization. [less ▲]

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See detailAnalysis of Early Science observations with the CHaracterising ExOPlanets Satellite (CHEOPS) using PYCHEOPS
Maxted, P. F. L.; Ehrenreich, D.; Wilson, T. G. et al

in Monthly Notices of the Royal Astronomical Society (2021)

CHEOPS (CHaracterising ExOPlanet Satellite) is an ESA S-class mission that observes bright stars at high cadence from low-Earth orbit. The main aim of the mission is to characterize exoplanets that ... [more ▼]

CHEOPS (CHaracterising ExOPlanet Satellite) is an ESA S-class mission that observes bright stars at high cadence from low-Earth orbit. The main aim of the mission is to characterize exoplanets that transit nearby stars using ultrahigh precision photometry. Here we report the analysis of transits observed by CHEOPS during its Early Science observing programme for four well-known exoplanets: GJ 436 b, HD 106315 b, HD 97658 b and GJ 1132 b. The analysis is done using PYCHEOPS, an open-source software package we have developed to easily and efficiently analyse CHEOPS light curve data using state-of-the-art techniques that are fully described herein. We show that the precision of the transit parameters measured using CHEOPS is comparable to that from larger space telescopes such as Spitzer Space Telescope and Kepler. We use the updated planet parameters from our analysis to derive new constraints on the internal structure of these four exoplanets. [less ▲]

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See detailNGTS clusters survey - III. A low-mass eclipsing binary in the Blanco 1 open cluster spanning the fully convective boundary
Smith, Gareth D.; Gillen, Edward; Queloz, Didier et al

in Monthly Notices of the Royal Astronomical Society (2021), 507

We present the discovery and characterization of an eclipsing binary identified by the Next Generation Transit Survey in the ~115-Myr-old Blanco 1 open cluster. NGTS J0002-29 comprises three M dwarfs: a ... [more ▼]

We present the discovery and characterization of an eclipsing binary identified by the Next Generation Transit Survey in the ~115-Myr-old Blanco 1 open cluster. NGTS J0002-29 comprises three M dwarfs: a short-period binary and a companion in a wider orbit. This system is the first well-characterized, low-mass eclipsing binary in Blanco 1. With a low mass ratio, a tertiary companion, and binary components that straddle the fully convective boundary, it is an important benchmark system, and one of only two well-characterized, low-mass eclipsing binaries at this age. We simultaneously model light curves from NGTS, TESS, SPECULOOS, and SAAO, radial velocities from VLT/UVES and Keck/HIRES, and the system's spectral energy distribution. We find that the binary components travel on circular orbits around their common centre of mass in Porb = 1.098 005 24 ± 0.000 000 38 d, and have masses Mpri = 0.3978 ± 0.0033 M⊙ and Msec = 0.2245 ± 0.0018 M⊙, radii Rpri = 0.4037 ± 0.0048 R⊙ and Rsec = 0.2759 ± 0.0055 R⊙, and effective temperatures $T_{\rm pri}=\mbox{$3372\, ^{+44}_{-37}$}$ K and $T_{\rm sec}=\mbox{$3231\, ^{+38}_{-31}$}$ K. We compare these properties to the predictions of seven stellar evolution models, which typically imply an inflated primary. The system joins a list of 19 well-characterized, low-mass, sub-Gyr, stellar-mass eclipsing binaries, which constitute some of the strongest observational tests of stellar evolution theory at low masses and young ages. [less ▲]

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See detailTOI-2257 b: A highly eccentric long-period sub-Neptune transiting a nearby M dwarf
Schanche, N.; Pozuelos, F. J.; Günther, M. N. et al

E-print/Working paper (2021)

Thanks to the relative ease of finding and characterizing small planets around M dwarf stars, these objects have become cornerstones in the field of exoplanet studies. The current paucity of planets in ... [more ▼]

Thanks to the relative ease of finding and characterizing small planets around M dwarf stars, these objects have become cornerstones in the field of exoplanet studies. The current paucity of planets in long-period orbits around M dwarfs make such objects particularly compelling as they provide clues about the formation and evolution of these systems. In this study, we present the discovery of TOI-2257 b (TIC 198485881), a long-period (35 d) sub-Neptune orbiting an M3 star at 57.8pc. Its transit depth is about 0.4%, large enough to be detected with medium-size, ground-based telescopes. The long transit duration suggests the planet is in a highly eccentric orbit ($e \sim 0.5$), which would make it the most eccentric planet that is known to be transiting an M-dwarf star. We combined TESS and ground-based data obtained with the 1.0-m SAINT-EX, 0.60-m TRAPPIST-North and 1.2-m FLWO telescopes to find a planetary size of 2.2 $R_{\oplus}$ and an orbital period of 35.19 days. In addition, we make use of archival data, high-resolution imaging, and vetting packages to support our planetary interpretation. With its long period and high eccentricity, TOI-2257 b falls in a novel slice of parameter space. Despite the planet's low equilibrium temperature ($\sim$ 256 K), its host star's small size ($R_* = 0.311 \pm{0.015}$) and relative infrared brightness (K$_{mag}$ = 10.7) make it a suitable candidate for atmospheric exploration via transmission spectroscopy. [less ▲]

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See detailWeather on Other Worlds. VI. Optical Spectrophotometry of Luhman 16B Reveals Large-amplitude Variations in the Alkali Lines
Heinze, A. N.; Metchev, Stanimir; Kurtev, Radostin et al

in Astrophysical Journal (2021), 920

Using a novel wide-slit, multiobject approach with the GMOS spectrograph on the 8 m Gemini South telescope, we have obtained precise time-series spectrophotometry of the binary brown dwarf Luhman 16 at ... [more ▼]

Using a novel wide-slit, multiobject approach with the GMOS spectrograph on the 8 m Gemini South telescope, we have obtained precise time-series spectrophotometry of the binary brown dwarf Luhman 16 at optical wavelengths over two full nights. The B component of this binary system is known to be variable in the red optical and near-infrared with a period of 5 hr and an amplitude of 5%-20%. Our observations probe its spectrally resolved variability in the 6000-10000 Å range. At wavelengths affected by the extremely strong, broadened spectral lines of the neutral alkali metals (the potassium doublet centered near 7682 Å and the sodium doublet at 5893 Å), we see photometric variations that differ strikingly from those of the 8000-10000 Å "red continuum" that dominates our detected flux. On UT 2014 February 24, these variations are anticorrelated with the red continuum, while on February 25 they have a large relative phase shift. The extent to which the wavelength-dependent photometric behavior diverges from that of the red continuum appears to correlate with the strength of the alkali absorption. We consider but ultimately reject models in which our observations are explained by lightning or auroral activity. A more likely cause is cloud-correlated, altitude-dependent variations in the gas-phase abundances of sodium and potassium, which are in chemical equilibrium with their chlorides in brown dwarf atmospheres. Clouds could influence these chemical equilibria by changing the atmospheric temperature profile and/or through cloud particles acting as chemical catalysts. [less ▲]

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See detailprose: A Python framework for modular astronomical images processing
Garcia, Lionel ULiege; Timmermans, Mathilde ULiege; Pozuelos, Francisco J. et al

in Monthly Notices of the Royal Astronomical Society (2021)

To reduce and analyse astronomical images, astronomers can rely on a wide range of libraries providing low-level implementations of legacy algorithms. However, combining these routines into robust and ... [more ▼]

To reduce and analyse astronomical images, astronomers can rely on a wide range of libraries providing low-level implementations of legacy algorithms. However, combining these routines into robust and functional pipelines requires a major effort which often ends up in instrument-specific and poorly maintainable tools, yielding products that suffer from a low-level of reproducibility and portability. In this context, we present prose, a Python framework to build modular and maintainable image processing pipelines. Built for astronomy, it is instrument-agnostic and allows the construction of pipelines using a wide range of building blocks, pre-implemented or user-defined. With this architecture, our package provides basic tools to deal with common tasks such as automatic reduction and photometric extraction. To demonstrate its potential, we use its default photometric pipeline to process 26 TESS candidates follow-up observations and compare their products to the ones obtained with AstroImageJ, the reference software for such endeavors. We show that prose produces light curves with lower white and red noise while requiring less user interactions and offering richer functionalities for reporting. [less ▲]

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See detailPhysical characterization of the active asteroid (6478) Gault from a multi-apparition campaign (2018-2020)
Devogele, Maxime; Ferrais, Marin ULiege; Jehin, Emmanuel ULiege et al

in Bulletin of the American Astronomical Society (2021, October 01), 53(7), 30904

(6478) Gault is a main-belt asteroid that was found to display cometary activity in late 2018-early 2019 [1]. During its 2018-2019 apparition, Gault experienced several activity events leading to the ... [more ▼]

(6478) Gault is a main-belt asteroid that was found to display cometary activity in late 2018-early 2019 [1]. During its 2018-2019 apparition, Gault experienced several activity events leading to the development of up to three distinct tails [2,3,4]. Many hypotheses such as impacts with smaller objects, YORP induced spin-up [5], sublimation of volatiles [6], or even the presence of a satellite in a highly eccentric and chaotic orbit, were considered to explain these events. <P />In this talk we present new photometric and spectroscopic observations of Gault obtained during the 2018-2019 and 2020 apparitions. These observations were obtained both when Gault was active (during the 2018-2019 apparition) and when it was found to be inactive during the 2020 apparition. For the first time we determine an accurate rotation period with high confidence of P=2.4929 ± 0.0003 h with a low amplitude of only 0.06 mag. This rotation period associated with a low lightcurve amplitude is consistent with a bulk density no smaller than 1.85 g cm3 in order for its activity to be triggered by the YORP spin-up mechanism. Our spectral analysis is consistent with Gault being of ordinary chondrite-like composition. Several spectra and a large datasets of broad band spectro-photometric observations obtained over the two oppositions do not show any sign of spectral variation over time. <P />Finally, we did not find any statistically significant signal of non-gravitational accelerations due to its activity even after the addition of previously unidentified detections of Gault dating back to 1958, which increased its orbital arc by a factor of almost 2. <P />These results were published in [7]. <P />References: <P />[1]: Smith K. W., Denneau L., Vincent J. B., et al., 2019, CBET, 4594 <P />[2]: Jehin E., Ferrais M., Moulane Y., et al. 2019, CBET, 4606 <P />[3]: Ye Q., et al., 2019, The ApJ Letters, 874, L16 <P />[4]: Jewitt D., Kim Y., Luu J., et al. 2019, The ApJ Letters, 876, L19 <P />[5]: Kleyna J. T., et al., 2019, The ApJ Letters, 874, L20 <P />[6]: Ferrín I., Fornari C., Acosta A., 2019, MNRAS, 490, 219 <P />[7]: Devogèle M., Ferrais M, Jehin E, et al. 2021, MNRAS, 505, 245 [less ▲]

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See detailThe HARPS search for southern extra-solar planets. XLVI. 12 super-Earths around the solar type stars HD 39194, HD 93385, HD 96700, HD 154088, and HD 189567
Unger, N.; Ségransan, D.; Queloz, D. et al

in Astronomy and Astrophysics (2021), 654

Context. We present precise radial-velocity measurements of five solar-type stars observed with the HARPS Echelle spectrograph mounted on the 3.6-m telescope in La Silla (ESO, Chile). With a time span of ... [more ▼]

Context. We present precise radial-velocity measurements of five solar-type stars observed with the HARPS Echelle spectrograph mounted on the 3.6-m telescope in La Silla (ESO, Chile). With a time span of more than 10 yr and a fairly dense sampling, the survey is sensitive to low mass planets down to super-Earths on orbital periods up to 100 days. <BR /> Aims: Our goal was to search for planetary companions around the stars HD 39194, HD 93385, HD 96700, HD 154088, and HD 189567 and use Bayesian model comparison to make an informed choice on the number of planets present in the systems based on the radial velocity observations. These findings will contribute to the pool of known exoplanets and better constrain their orbital parameters. <BR /> Methods: A first analysis was performed using the Data & Analysis Center for Exoplanets online tools to assess the activity level of the star and the potential planetary content of each system. We then used Bayesian model comparison on all targets to get a robust estimate on the number of planets per star. We did this using the nested sampling algorithm POLYCHORD. For some targets, we also compared different noise models to disentangle planetary signatures from stellar activity. Lastly, we ran an efficient Markov chain Monte Carlo algorithm for each target to get reliable estimates for the planets' orbital parameters. <BR /> Results: We identify 12 planets within several multiplanet systems. These planets are all in the super-Earth and sub-Neptune mass regime with minimum masses ranging between 4 and 13 M[SUB]⊕[/SUB] and orbital periods between 5 and 103 days. Three of these planets are new, namely HD 93385 b, HD 96700 c, and HD 189567 c. <P />RV data are only available at the CDS via anonymous ftp to <A href="http://cdsarc.u-strasbg.fr">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/654/A104">http://cdsarc.u-strasbg.fr/viz-bin/cat/J/A+A/654/A104</A> <P />Based on observations made with HARPS spectrograph on the 3.6-m ESO telescope at La Silla Observatory, Chile. [less ▲]

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See detailDetecting life outside our solar system with a large high-contrast-imaging mission
Snellen, Ignas A. G.; Snik, F.; Kenworthy, M. et al

in Experimental Astronomy (2021)

In this White Paper, which was submitted in response to the European Space Agency (ESA) Voyage 2050 Call, we recommend the ESA plays a proactive role in developing a global collaborative effort to ... [more ▼]

In this White Paper, which was submitted in response to the European Space Agency (ESA) Voyage 2050 Call, we recommend the ESA plays a proactive role in developing a global collaborative effort to construct a large high-contrast imaging space telescope, e.g. as currently under study by NASA. Such a mission will be needed to characterize a sizable sample of temperate Earth-like planets in the habitable zones of nearby Sun-like stars and to search for extraterrestrial biological activity. We provide an overview of relevant European expertise, and advocate ESA to start a technology development program towards detecting life outside the Solar System. [less ▲]

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See detailThe changing face of AU Mic b: stellar spots, spin-orbit commensurability, and transit timing variations as seen by CHEOPS and TESS
Szabó, Gy M.; Gandolfi, D.; Brandeker, A. et al

in Astronomy and Astrophysics (2021), 654

AU Mic is a young planetary system with a resolved debris disc showing signs of planet formation and two transiting warm Neptunes near mean-motion resonances. Here we analyse three transits of AU Mic b ... [more ▼]

AU Mic is a young planetary system with a resolved debris disc showing signs of planet formation and two transiting warm Neptunes near mean-motion resonances. Here we analyse three transits of AU Mic b observed with the CHaracterising ExOPlanet Satellite (CHEOPS), supplemented with sector 1 and 27 Transiting Exoplanet Survey Satellite (TESS) photometry, and the All-Sky Automated Survey from the ground. The refined orbital period of AU Mic b is 8.462995 ± 0.000003 d, whereas the stellar rotational period is P[SUB]rot[/SUB] = 4.8367 ± 0.0006 d. The two periods indicate a 7:4 spin-orbit commensurability at a precision of 0.1%. Therefore, all transits are observed in front of one of the four possible stellar central longitudes. This is strongly supported by the observation that the same complex star-spot pattern is seen in the second and third CHEOPS visits that were separated by four orbits (and seven stellar rotations). Using a bootstrap analysis we find that flares and star spots reduce the accuracy of transit parameters by up to 10% in the planet-to-star radius ratio and the accuracy on transit time by 3-4 min. Nevertheless, occulted stellar spot features independently confirm the presence of transit timing variations (TTVs) with an amplitude of at least 4 min. We find that the outer companion, AU Mic c, may cause the observed TTVs. [less ▲]

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See detailTOI-674b: An oasis in the desert of exo-Neptunes transiting a nearby M dwarf
Murgas, F.; Astudillo-Defru, N.; Bonfils, X. et al

in Astronomy and Astrophysics (2021), 653

Context. The NASA mission TESS is currently doing an all-sky survey from space to detect transiting planets around bright stars. As part of the validation process, the most promising planet candidates ... [more ▼]

Context. The NASA mission TESS is currently doing an all-sky survey from space to detect transiting planets around bright stars. As part of the validation process, the most promising planet candidates need to be confirmed and characterized using follow-up observations. Aims: In this article, our aim is to confirm the planetary nature of the transiting planet candidate TOI-674b using spectroscopic and photometric observations. Methods: We use TESS, Spitzer, ground-based light curves, and HARPS spectrograph radial velocity measurements to establish the physical properties of the transiting exoplanet candidate TOI-674b. We perform a joint fit of the light curves and radial velocity time series to measure the mass, radius, and orbital parameters of the candidate. Results: We confirm and characterize TOI-674b, a low-density super-Neptune transiting a nearby M dwarf. The host star (TIC 158588995, V = 14.2 mag, J = 10.3 mag) is characterized by its M2V spectral type with M⋆ = 0.420 ± 0.010 M⊙, R⋆ = 0.420 ± 0.013 R⊙, and Teff = 3514 ± 57 K; it is located at a distance d = 46.16 ± 0.03 pc. Combining the available transit light curves plus radial velocity measurements and jointly fitting a circular orbit model, we find an orbital period of 1.977143 ± 3 × 10^−6 days, a planetary radius of 5.25 ± 0.17 R⊕, and a mass of 23.6 ± 3.3 M⊕ implying a mean density of ρ_p =0.91 ± 0.15 g cm^−3. A non-circular orbit model fit delivers similar planetary mass and radius values within the uncertainties. Given the measured planetary radius and mass, TOI-674b is one of the largest and most massive super-Neptune class planets discovered around an M-type star to date. It is found in the Neptunian desert, and is a promising candidate for atmospheric characterization using the James Webb Space Telescope. [less ▲]

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See detailA large sub-Neptune transiting the thick-disk M4 V TOI-2406
Wells, R. D.; Rackham, B. V.; Schanche, N. et al

in Astronomy and Astrophysics (2021), 653

Context. Large sub-Neptunes are uncommon around the coolest stars in the Galaxy and are rarer still around those that are metal-poor. However, owing to the large planet-to-star radius ratio, these planets ... [more ▼]

Context. Large sub-Neptunes are uncommon around the coolest stars in the Galaxy and are rarer still around those that are metal-poor. However, owing to the large planet-to-star radius ratio, these planets are highly suitable for atmospheric study via transmission spectroscopy in the infrared, such as with JWST. Aims: Here we report the discovery and validation of a sub-Neptune orbiting the thick-disk, mid-M dwarf star TOI-2406. The star's low metallicity and the relatively large size and short period of the planet make TOI-2406 b an unusual outcome of planet formation, and its characterisation provides an important observational constraint for formation models. Methods: We first infer properties of the host star by analysing the star's near-infrared spectrum, spectral energy distribution, and Gaia parallax. We use multi-band photometry to confirm that the transit event is on-target and achromatic, and we statistically validate the TESS signal as a transiting exoplanet. We then determine physical properties of the planet through global transit modelling of the TESS and ground-based time-series data. Results: We determine the host to be a metal-poor M4 V star, located at a distance of 56 pc, with properties Teff = 3100 ± 75 K, M* = 0.162 ± 0.008M⊙, R* = 0.202 ± 0.011R⊙, and [Fe∕H] = −0.38 ± 0.07, and a member of the thick disk. The planet is a relatively large sub-Neptune for the M-dwarf planet population, with Rp = 2.94 ± 0.17R⊕ and P= 3.077 d, producing transits of 2% depth. We note the orbit has a non-zero eccentricity to 3σ, prompting questions about the dynamical history of the system. Conclusions: This system is an interesting outcome of planet formation and presents a benchmark for large-planet formation around metal-poor, low-mass stars. The system warrants further study, in particular radial velocity follow-up to determine the planet mass and constrain possible bound companions. Furthermore, TOI-2406 b is a good target for future atmospheric study through transmission spectroscopy. Although the planet's mass remains to be constrained, we estimate the S/N using amass-radius relationship, ranking the system fifth in the population of large sub-Neptunes, with TOI-2406 b having a much lower equilibrium temperature than other spectroscopically accessible members of this population. [less ▲]

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See detailDiscovery of a young low-mass brown dwarf transiting a fast-rotating F-type star by the Galactic Plane eXoplanet (GPX) survey
Benni, P.; Burdanov, A. Y.; Krushinsky, V. V. et al

in Monthly Notices of the Royal Astronomical Society (2021), 505

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 ... [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 ▲]

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See detail(6478) Gault: physical characterization of an active main-belt asteroid
Devogèle, Maxime; Ferrais, Marin ULiege; Jehin, Emmanuel ULiege et al

in Monthly Notices of the Royal Astronomical Society (2021), 505

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 ... [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 ▲]

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See detailWarm Jupiters in TESS Full-frame Images: A Catalog and Observed Eccentricity Distribution for Year 1
Dong, Jiayin; Huang, Chelsea X.; Dawson, Rebekah I. et al

in Astrophysical Journal Supplement Series (2021), 255

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 ... [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 ▲]

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See detailTransit detection of the long-period volatile-rich super-Earth \nu^2 Lupi d with CHEOPS
Delrez, Laetitia ULiege; Ehrenreich, David; Alibert, Yann et al

in 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 ▲]

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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 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 (2021), 650

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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