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Amaury H. M. J. Triaud

Publications and source records attributed to Amaury H. M. J. Triaud.

At least 55 records · Page 3Linked to original sources
arXiv2024

An extended low-density atmosphere around the Jupiter-sized planet WASP-193 b

Gas giants transiting bright nearby stars provide crucial insights into planetary system formation and evolution mechanisms. Most of these planets exhibit certain average characteristics, serving as benchmarks for our understanding of planetary systems. However, outliers like the planet we present in this study, WASP-193b, offer unique opportunities to explore unconventional formation and evolution processes. This planet completes an orbit around its Vmag=12.2 F9 main-sequence host star every 6.25 d. Our analyses found that WASP-193b has a mass of Mp=0.139+/-0.029 MJup and a radius of Rp=1.464+/-0.058 RJup, translating into an extremely low density of rho_p = 0.059+/-0.014 g/cm^3, at least one order of magnitude less than standard gas giants like Jupiter. Typical gas giants such as Jupiter have densities that range between 0.2 and 2 g/cm^3. The combination of its large transit depth (dF~1.4%), its extremely-low density, its high-equilibrium temperature (Teq = 1254+/-31 K), and the infrared brightness of its host star (magnitude Kmag=10.7) makes WASP-193b an exquisite target for characterization by transmission spectroscopy (transmission spectroscopy metric: TSM~600). One single JWST transit observation would yield detailed insights into its atmospheric properties and planetary mass, providing a unique window to explore the mechanisms behind its exceptionally low density and shed light on giant planets' diverse nature.

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arXiv2024

TOI 762 A b and TIC 46432937 b: Two Giant Planets Transiting M Dwarf Stars

We present the discovery of TOI 762 A b and TIC 46432937 b, two giant planets transiting M dwarf stars. Transits of both systems were first detected from observations by the NASA TESS mission, and the transiting objects are confirmed as planets through high-precision radial velocity (RV) observations carried out with VLT/ESPRESSO. TOI 762 A b is a warm sub-Saturn with a mass of 0.251 +- 0.042 M_J, a radius of 0.744 +- 0.017 R_J, and an orbital period of 3.4717 d. It transits a mid-M dwarf star with a mass of 0.442 +- 0.025 M_S and a radius of 0.4250 +- 0.0091 R_S. The star TOI 762 A has a resolved binary star companion TOI 762 B that is separated from TOI 762 A by 3.2" (~ 319 AU) and has an estimated mass of 0.227 +- 0.010 M_S. The planet TIC 46432937 b is a warm Super-Jupiter with a mass of 3.20 +- 0.11 M_J and radius of 1.188 +- 0.030 R_J. The planet's orbital period is P = 1.4404 d, and it undergoes grazing transits of its early M dwarf host star, which has a mass of 0.563 +- 0.029 M_S and a radius of 0.5299 +- 0.0091 R_S. TIC 46432937 b is one of the highest mass planets found to date transiting an M dwarf star. TIC 46432937 b is also a promising target for atmospheric observations, having the highest Transmission Spectroscopy Metric or Emission Spectroscopy Metric value of any known warm Super-Jupiter (mass greater than 3.0 M_J, equilibrium temperature below 1000 K).

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arXiv2024

TESS Hunt for Young and Maturing Exoplanets (THYME) X: a two-planet system in the 210 Myr MELANGE-5 Association

Young (<500 Myr) planets are critical to studying how planets form and evolve. Among these young planetary systems, multi-planet configurations are particularly useful as they provide a means to control for variables within a system. Here, we report the discovery and characterization of a young planetary system, TOI-1224. We show that the planet-host resides within a young population we denote as MELANGE-5 . By employing a range of age-dating methods -- isochrone fitting, lithium abundance analysis, gyrochronology, and Gaia excess variability -- we estimate the age of MELANGE-5 to be 210$\pm$27 Myr. MELANGE-5 is situated in close proximity to previously identified younger (80 -110 Myr) associations, Crius 221 and Theia 424/Volans-Carina, motivating further work to map out the group boundaries. In addition to a planet candidate detected by the TESS pipeline and alerted as a TESS Object of Interest, TOI-1224 b, we identify a second planet, TOI-1224 c, using custom search tools optimized for young stars (Notch and LOCoR). We find the planets are 2.10$\pm$0.09$R_\oplus$ and 2.88$\pm$0.10$R_\oplus$ and orbit their host star every 4.18 and 17.95 days, respectively. With their bright ($K$=9.1 mag), small ($R_{*}$=0.44R$_{\odot}$), and cool ($T_{eff}$ =3326K) host star, these planets represent excellent candidates for atmospheric characterization with JWST.

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arXiv2024

BEBOP V. Homogeneous Stellar Analysis of Potential Circumbinary Planet Hosts

Planets orbiting binary systems are relatively unexplored compared to those around single stars. Detections of circumbinary planets and planetary systems offer a first detailed view into our understanding of circumbinary planet formation and dynamical evolution. The BEBOP (Binaries Escorted by Orbiting Planets) radial velocity survey plays a special role in this adventure as it focuses on eclipsing single-lined binaries with an FGK dwarf primary and M dwarf secondary allowing for the highest-radial velocity precision using the HARPS and SOPHIE spectrographs. We obtained 4512 high-resolution spectra for the 179 targets in the BEBOP survey which we used to derive the stellar atmospheric parameters using both equivalent widths and spectral synthesis. We furthermore derive stellar masses, radii, and ages for all targets. With this work, we present the first homogeneous catalogue of precise stellar parameters for these eclipsing single-lined binaries.

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arXiv2024

Detection of an Earth-sized exoplanet orbiting the nearby ultracool dwarf star SPECULOOS-3

Located at the bottom of the main sequence, ultracool dwarf stars are widespread in the solar neighbourhood. Nevertheless, their extremely low luminosity has left their planetary population largely unexplored, and only one of them, TRAPPIST-1, has so far been found to host a transiting planetary system. In this context, we present the SPECULOOS project's detection of an Earth-sized planet in a 17 h orbit around an ultracool dwarf of M6.5 spectral type located 16.8 pc away. The planet's high irradiation (16 times that of Earth) combined with the infrared luminosity and Jupiter-like size of its host star make it one of the most promising rocky exoplanet targets for detailed emission spectroscopy characterization with JWST. Indeed, our sensitivity study shows that just ten secondary eclipse observations with the Mid-InfraRed Instrument/Low-Resolution Spectrometer on board JWST should provide strong constraints on its atmospheric composition and/or surface mineralogy.

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arXiv2024

The EBLM Project XII. An eccentric, long-period eclipsing binary with a companion near the hydrogen-burning limit

In the hunt for Earth-like exoplanets it is crucial to have reliable host star parameters, as they have a direct impact on the accuracy and precision of the inferred parameters for any discovered exoplanet. For stars with masses between 0.35 and 0.5 ${\rm M_{\odot}}$ an unexplained radius inflation is observed relative to typical stellar models. However, for fully convective objects with a mass below 0.35 ${\rm M_{\odot}}$ it is not known whether this radius inflation is present as there are fewer objects with accurate measurements in this regime. Low-mass eclipsing binaries present a unique opportunity to determine empirical masses and radii for these low-mass stars. Here we report on such a star, EBLM J2114-39\,B. We have used HARPS and FEROS radial-velocities and \textit{TESS} photometry to perform a joint fit of the data, and produce one of the most precise estimates of a very low mass star's parameters. Using a precise and accurate radius for the primary star using {\it Gaia} DR3 data, we determine J2114-39 to be a $M_1 = 0.998 \pm 0.052$~${\rm M_{\odot}}$ primary star hosting a fully convective secondary with mass $M_2~=~0.0986~\pm 0.0038~\,\mathrm{M_{\odot}}$, which lies in a poorly populated region of parameter space. With a radius $R_2 =~0.1275~\pm0.0020~\,\mathrm{R_{\odot}}$, similar to TRAPPIST-1, we see no significant evidence of radius inflation in this system when compared to stellar evolution models. We speculate that stellar models in the regime where radius inflation is observed might be affected by how convective overshooting is treated.

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arXiv2024

Three Warm Jupiters around Solar-analog stars detected with TESS

We report the discovery and characterization of three giant exoplanets orbiting solar-analog stars, detected by the \tess space mission and confirmed through ground-based photometry and radial velocity (RV) measurements taken at La Silla observatory with \textit{FEROS}. TOI-2373\,b is a warm Jupiter orbiting its host star every $\sim$ 13.3 days, and is one of the two most massive known exoplanet with a precisely determined mass and radius around a star similar to the Sun, with an estimated mass of m$_p$ = $9.3^{+0.2}_{-0.2}\,M_{\mathrm{jup}}$, and a radius of $r_p$ = $0.93^{+0.2}_{-0.2}\,R_{\mathrm{jup}}$. With a mean density of $ρ= 14.4^{+0.9}_{-1.0}\,\mathrm{g\,cm}^{-3}$, TOI-2373\,b is among the densest planets discovered so far. TOI-2416\,b orbits its host star on a moderately eccentric orbit with a period of $\sim$ 8.3 days and an eccentricity of $e$ = $0.32^{+0.02}_{-0.02}$. TOI-2416\,b is more massive than Jupiter with $m_p$ = 3.0$^{+0.10}_{-0.09}\,M_{\mathrm{jup}}$, however is significantly smaller with a radius of $r_p$ = $0.88^{+0.02}_{-0.02},R_{\mathrm{jup}}$, leading to a high mean density of $ρ= 5.4^{+0.3}_{-0.3}\,\mathrm{g\,cm}^{-3}$. TOI-2524\,b is a warm Jupiter near the hot Jupiter transition region, orbiting its star every $\sim$ 7.2 days on a circular orbit. It is less massive than Jupiter with a mass of $m_p$ = $0.64^{+0.04}_{-0.04}\,M_{\mathrm{jup}}$, and is consistent with an inflated radius of $r_p$ = $1.00^{+0.02}_{-0.03}\,R_{\mathrm{jup}}$, leading to a low mean density of $ρ= 0.79^{+0.08}_{-0.08}\,\mathrm{g\,cm}^{-3}$. The newly discovered exoplanets TOI-2373\,b, TOI-2416\,b, and TOI-2524\,b have estimated equilibrium temperatures of $860^{+10}_{-10}$ K, $1080^{+10}_{-10}$ K, and $1100^{+20}_{-20}$ K, respectively, placing them in the sparsely populated transition zone between hot and warm Jupiters.

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arXiv2024

NGTS-28Ab: A short period transiting brown dwarf

We report the discovery of a brown dwarf orbiting a M1 host star. We first identified the brown dwarf within the Next Generation Transit Survey data, with supporting observations found in TESS sectors 11 and 38. We confirmed the discovery with follow-up photometry from the South African Astronomical Observatory, SPECULOOS-S, and TRAPPIST-S, and radial velocity measurements from HARPS, which allowed us to characterise the system. We find an orbital period of ~1.25 d, a mass of 69.0+5.3-4.8 MJ, close to the Hydrogen burning limit, and a radius of 0.95 +- 0.05 RJ. We determine the age to be >0.5 Gyr, using model isochrones, which is found to be in agreement with SED fitting within errors. NGTS-28Ab is one of the shortest period systems found within the brown dwarf desert, as well as one of the highest mass brown dwarfs that transits an M dwarf. This makes NGTS-28Ab another important discovery within this scarcely populated region.

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arXiv2024

Saltire -- A model to measure dynamical masses for high-contrast binaries and exoplanets with high-resolution spectroscopy

High-resolution cross-correlation methods are widely used to discover and to characterise atomic and molecular species in exoplanet atmospheres. The characteristic cross-correlation signal is typically represented as a function of the velocity of the system, and the semi-amplitude of the planet's orbit. We present Saltire, a fast and simple model that accurately reproduces the shape of such cross-correlation signals, allowing a direct fit to the data by using a minimum set of parameters. We show how to use this model on the detection of atmospheric CO in archival data of the hot Jupiter tau Bootis b, and how Saltire can be used to estimate the semi-amplitude and rest velocity of high brightness-ratio binaries. By including the shape of the signal, we demonstrate that our model allows to robustly derive the signal position up to 10 times more accurate, compared to conventional methods. Furthermore, we discuss the impact of correlated noise and demonstrate that Saltire is a robust tool for estimating systematic uncertainties on the signal position. Saltire opens a new door to analyse high signal-to-noise data to accurately study atmospheric dynamics and to measure precise dynamical masses for exoplanets and faint stellar companions. We show, that the phase-resolved shape of the atmospheric CCF signal can accurately be reproduced, allowing studies of phase-dependent signal changes and to disentangle them from noise and data aliases.

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arXiv2024

A long-period transiting substellar companion in the super-Jupiters to brown dwarfs mass regime and a prototypical warm-Jupiter detected by TESS

We report on the confirmation and follow-up characterization of two long-period transiting substellar companions on low-eccentricity orbits around TIC 4672985 and TOI-2529, whose transit events were detected by the TESS space mission. Ground-based photometric and spectroscopic follow-up from different facilities, confirmed the substellar nature of TIC 4672985 b, a massive gas giant, in the transition between the super Jupiters and brown dwarfs mass regime. From the joint analysis we derived the following orbital parameters: P = 69.0480 d, Mp = 12.74 Mjup, Rp = 1.026 Rjup and e = 0.018. In addition, the RV time series revealed a significant trend at the 350 m/s/yr level, which is indicative of the presence of a massive outer companion in the system. TIC 4672985 b is a unique example of a transiting substellar companion with a mass above the deuterium-burning limit, located beyond 0.1 AU and in a nearly circular orbit. These planetary properties are difficult to reproduce from canonical planet formation and evolution models. For TOI-2529 b, we obtained the following orbital parameters: P = 64.5949 d, Mp = 2.340 Mjup, Rp = 1.030 Rjup and e = 0.021, making this object a new example of a growing population of transiting warm giant planets.

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arXiv2024

ESPRESSO observations of Gaia BH1: high-precision orbital constraints and no evidence for an inner binary

We present high-precision radial velocity (RV) observations of Gaia BH1, the nearest known black hole (BH). The system contains a solar-type G star orbiting a massive dark companion, which could be either a single BH or an inner BH + BH binary. A BH + BH binary is expected in some models where Gaia BH1 formed as a hierarchical triple, which are attractive because they avoid many of the difficulties associated with forming the system through isolated binary evolution. Our observations test the inner binary scenario. We have measured 115 precise RVs of the G star, including 40 from ESPRESSO with a precision of $3$-$5$ m s$^{-1}$, and 75 from other instruments with a typical precision of $30$-$100$ m s$^{-1}$. Our observations span $2.33$ orbits of the G star and are concentrated near a periastron passage, when perturbations due to an inner binary would be largest. The RVs are well-fit by a Keplerian two-body orbit and show no convincing evidence of an inner binary. Using REBOUND simulations of hierarchical triples with a range of inner periods, mass ratios, eccentricities, and orientations, we show that plausible inner binaries with periods $P_{\text{inner}} \gtrsim 1.5$ days would have produced larger deviations from a Keplerian orbit than observed. Binaries with $P_{\text{inner}} \lesssim 1.5$ days are consistent with the data, but these would merge within a Hubble time and would thus imply fine-tuning. We present updated parameters of Gaia BH1's orbit. The RVs yield a spectroscopic mass function $f\left(M_{\text{BH}}\right)=3.9358 \pm 0.0002\,M_{\odot}$ - about $7000σ$ above the $\sim2.5\,M_{\odot}$ maximum neutron star mass. Including the inclination constraint from Gaia astrometry, this implies a BH mass of $M_{\text{BH}} = 9.27 \pm 0.10 ~ M_{\odot}$.

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arXiv2024

The EBLM project X. Benchmark masses, radii and temperatures for two fully convective M-dwarfs using K2

M-dwarfs are the most abundant stars in the galaxy and popular targets for exoplanet searches. However, their intrinsic faintness and complex spectra inhibit precise characterisation. We only know of dozens of M-dwarfs with fundamental parameters of mass, radius and effective temperature characterised to better than a few per cent. Eclipsing binaries remain the most robust means of stellar characterisation. Here we present two targets from the Eclipsing Binary Low Mass (EBLM) survey that were observed with K2: EBLM J0055-00 and EBLM J2217-04. Combined with HARPS and CORALIE spectroscopy, we measure M-dwarf masses with precisions better than 5%, radii better than 3% and effective temperatures on order 1%. However, our fits require invoking a model to derive parameters for the primary star. By investigating three popular models, we determine that the model uncertainty is of similar magnitude to the statistical uncertainty in the model fits. Therefore, whilst these can be considered benchmark M-dwarfs, we caution the community to consider model uncertainty when pushing the limits of precise stellar characterisation.

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arXiv2024

Atmospheric carbon depletion as a tracer of water oceans and biomass on temperate terrestrial exoplanets

The conventional observables to identify a habitable or inhabited environment in exoplanets, such as an ocean glint or abundant atmospheric O$_2$, will be challenging to detect with present or upcoming observatories. Here we suggest a new signature. A low carbon abundance in the atmosphere of a temperate rocky planet, relative to other planets of the same system, traces the presence of substantial amount of liquid water, plate tectonic and/or biomass. We show that JWST can already perform such a search in some selected systems like TRAPPIST-1 via the CO$_2$ band at $4.3\,\rm μm$, which falls in a spectral sweet spot where the overall noise budget and the effect of cloud/hazes are optimal. We propose a 3-step strategy for transiting exoplanets: 1) detection of an atmosphere around temperate terrestrial planets in $\sim 10$ transits for the most favorable systems, (2) assessment of atmospheric carbon depletion in $\sim 40$ transits, (3) measurements of O$_3$ abundance to disentangle between a water- vs biomass-supported carbon depletion in $\sim100$ transits. The concept of carbon depletion as a signature for habitability is also applicable for next-generation direct imaging telescopes.

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arXiv2023

Constraining the formation history of the TOI-1338/BEBOP-1 circumbinary planetary system

The recent discovery of multiple planets in the circumbinary system TOI-1338/BEBOP-1 raises questions about how such a system formed. The formation of the system was briefly explored in the discovery paper, but only to answer the question do current pebble accretion models have the potential to explain the origin of the system? We use a global model of circumbinary planet formation that utilises N-body simulations, including prescriptions for planet migration, gas and pebble accretion, and interactions with a circumbinary disc, to explore the disc parameters that could have led to the formation of the TOI-1338/BEBOP-1 system. With the disc lifetime being the main factor in determining how planets form, we limit our parameter space to those that determine the disc lifetime. These are: the strength of turbulence in the disc, the initial disc mass, and the strength of the external radiation field that launches photoevaporative winds. When comparing the simulated systems to TOI-1338/BEBOP-1, we find that only discs with low levels of turbulence are able to produce similar systems. The radiation environment has a large effect on the types of planetary systems that form, whilst the initial disc mass only has limited impact since the majority of planetary growth occurs early in the disc lifetime. With the most TOI-1338/BEBOP-1 like systems all occupying similar regions of parameter space, our study shows that observed circumbinary planetary systems can potentially constrain the properties of planet forming discs.

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arXiv2023

New methods for radial-velocity measurements of double-lined binaries, and detection of a circumbinary planet orbiting TIC 172900988

Ongoing ground-based radial-velocity observations seeking to detect circumbinary planets focus on single-lined binaries even though over nine in every ten binary systems in the solar-neighbourhood are double-lined. Double-lined binaries are on average brighter, and should in principle yield more precise radial-velocities. However, as the two stars orbit one another, they produce a time-varying blending of their weak spectral lines. This makes an accurate measure of radial velocities difficult, producing a typical scatter of 10-15m/s. This extra noise prevents the detection of most orbiting circumbinary planets. We develop two new data-driven approaches to disentangle the two stellar components of a double-lined binary, and extract accurate and precise radial-velocities. Both approaches use a Gaussian Process regression, with the first one working in the spectral domain, whereas the second works on cross-correlated spectra. We apply our new methods to TIC 172900988, a proposed circumbinary system with a double-lined binary, and detect a circumbinary planet with an orbital period of 150 days, different than previously proposed. We also measure a significant residual scatter, which we speculate is caused by stellar activity. We show that our two data-driven methods outperform the traditionally used TODCOR and TODMOR, for that particular binary system.

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arXiv2023

TOI-199 b: A well-characterized 100-day transiting warm giant planet with TTVs seen from Antarctica

We present the spectroscopic confirmation and precise mass measurement of the warm giant planet TOI-199 b. This planet was first identified in TESS photometry and confirmed using ground-based photometry from ASTEP in Antarctica including a full 6.5$\,$h long transit, PEST, Hazelwood, and LCO; space photometry from NEOSSat; and radial velocities (RVs) from FEROS, HARPS, CORALIE, and CHIRON. Orbiting a late G-type star, TOI-199\,b has a $\mathrm{104.854_{-0.002}^{+0.001} \, d}$ period, a mass of $\mathrm{0.17\pm0.02 \, M_J}$, and a radius of $\mathrm{0.810\pm0.005 \, R_J}$. It is the first warm exo-Saturn with a precisely determined mass and radius. The TESS and ASTEP transits show strong transit timing variations, pointing to the existence of a second planet in the system. The joint analysis of the RVs and TTVs provides a unique solution for the non-transiting companion TOI-199 c, which has a period of $\mathrm{273.69_{-0.22}^{+0.26} \, d}$ and an estimated mass of $\mathrm{0.28_{-0.01}^{+0.02} \, M_J}$. This period places it within the conservative Habitable Zone.

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arXiv2023

Transit Timing Variations in the three-planet system: TOI-270

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 $\sim$10 minutes and a super-period of $\sim$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 $M_{\mathrm{b}}=1.48\pm0.18\,M_\oplus$, $M_{c}=6.20\pm0.31\,M_\oplus$ and $M_{\mathrm{d}}=4.20\pm0.16\,M_\oplus$ for planets b, c and d, respectively. We also detect small, but significant eccentricities for all three planets : $e_\mathrm{b} =0.0167\pm0.0084$, $e_{c} =0.0044\pm0.0006$ and $e_{d} = 0.0066\pm0.0020$. Our findings imply an Earth-like rocky composition for the inner planet, and Earth-like cores with an additional He/H$_2$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.

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arXiv2023

The Orbit of Warm Jupiter WASP-106 b is aligned with its Star

Understanding orbital obliquities, or the misalignment angles between a star's rotation axis and the orbital axis of its planets, is crucial for unraveling the mechanisms of planetary formation and migration. In this study, we present an analysis of Rossiter-McLaughlin (RM) observations of the warm Jupiter exoplanet WASP-106 b. The high-precision radial velocity measurements were made with HARPS and HARPS-N during the transit of this planet. We aim to constrain the orientation of the planet's orbit relative to its host star's rotation axis. The RM observations are analyzed using a code which models the RM anomaly together with the Keplerian orbit given several parameters in combination with a Markov chain Monte Carlo implementation. We measure the projected stellar obliquity in the WASP-106 system for the first time and find $λ= (-1 \pm 11)^\circ$, supporting the theory of quiescent migration through the disk.

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