arXiv subjects

E. Fontanet

Publications and source records attributed to E. Fontanet.

8 recordsLinked to original sources

arXiv2026

Transit timing and starspot-induced transit depth variations in the $\sim$17 Myr old HIP 67522 system

HIP 67522 is a one of the youngest multi-planetary systems discovered to date. The 17 Myr-old, Sun-like star is part of the Scorpius-Centarus OB association and is known to host two Saturn-sized planets in near 2:1 mean motion resonance. We analysed photometric transits observed with the CHaracterising ExOPlanet Satellite (CHEOPS), the Transiting Exoplanets Survey Satellite (TESS) and multiple ground-based facilities to search for transit timing variations induced by planet-planet gravitational interactions, as well as transit depth variations, linked with the changing coverage of active regions on the stellar surface. We do not detect any transit timing variations for HIP 67522 b exceeding two minutes, contrary to previous results from the James Webb Space Telescope. In addition, we found that the observed transit depth of planet b changes strongly over time, with a >30\% variation in amplitude. The high sensitivity and blue bandpass of the CHEOPS satellite also enabled us to identify multiple starspot crossings and measure their properties, including spot temperatures and sizes. We also measured the shear of the host star's differential rotation by modelling the out-of-transit photometric variability and concluded that HIP 67522 exhibits a supersolar differential rotation. Based on internal structure models and planet formation simulations, we find that HIP 67522 b likely have more than 20\% of their mass made of gaseous envelopes at their current age. Evolutionary simulations further indicate that both planets in the system will experience significant photoevaporation, evolving into either Earth size planets with completely stripped atmospheres or sub-Neptune-sized planets.

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arXiv2026

CORALIE radial-velocity search for companions around evolved stars (CASCADES) V. Three planetary companions and achievable precision

Aims. We expand the planetary census around massive stellar hosts through a long-term campaign of high-precision radial velocity (RV) measurements on evolved stars. Methods. We analyse data acquired with the CORALIE spectrograph covering 15-18 years on HD125136, HD127195, and HD220218. Stellar parameters are derived through different methods for a comprehensive characterization of each star. We then evaluate the presence of planetary signals in the RV time series using the Bayesian inference tool kima. Finally, we design an observing strategy aimed at mitigating the impact of pulsations on evolved stars and test its effectiveness on the low-luminosity red giant HD127195. Results. We detect signals that are accurately modelled by Keplerian curves in the RV data of the three stars: one on HD 125136, two on HD 127195, and one on HD 220218. While the signals on the first two stars seem to be of planetary origin, the signal on the third one shows several signs of stellar activity. We therefore identify a planetary companion around HD125136 with a minimum mass of 2.26 MJup on an 850 d orbit, and on HD127195 we identify a system composed of planets with 0.66 MJup and 0.78 MJup with orbital periods of 535 d and 834 d, respectively. Conclusions. We detect three massive planets around two low-luminosity red giant stars in a region of the parameter space that is poorly populated in both stellar mass and planetary orbital periods. The dedicated observing campaign on HD127195 showcases how stellar pulsations can be efficiently averaged out to below 5 m/s in low-luminosity giant stars.

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arXiv2026

Photodynamical modeling of TOI-4504 reveals its deeply resonant state and similarity to GJ 876

The K-dwarf TOI-4504 hosts two giant planets in 2:1 mean-motion resonance, with orbital periods of 41.3 days (planet d) and 82.8 days (planet c). They exhibit among the largest known absolute transit-timing variations, with respective peak-to-node amplitudes up to 5 and 3 days. Newer TESS data show that the previously non-transiting planet d has now precessed into transiting, and we derive updated system parameters with significant discrepancies with the discovery paper. The revised parameters place planets d and c deep in the resonance and close to or in the fully-relaxed limit-cycle state, with the resonant and secular modes interfering nonlinearly to induce non-zero relaxed free eccentricities which precess at the same rate as the forced eccentricities and the longitude of conjunctions, in turn enabling precise measurement of the full eccentricities and apsidal angles. We discuss the predictions of linear theory and how it can be used to understand the true state of the system revealed by N-body integrations, and more generally why it is that the posteriors of systems more compact than 2:1 tend to suffer from significant eccentricity degeneracy. We show that the extraordinary dynamical states of the giant pairs orbiting TOI-4504 and the M-dwarf GJ 876 are remarkably similar, in spite of the significant difference in their host-star masses, and discuss the implications for damping timescales during the relatively gentle formation process of Type II migration.

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arXiv2025

A decade of transit photometry for K2-19: Revised system architecture

The star K2-19 hosts a pair of Neptunian planets deep inside the 3:2 resonance. They induce strong transit-timing variations with two incommensurate frequencies. Previous photodynamical modeling of 3.3 years of transit and radial velocity data produced mass estimates of 32.4 +/- 1.7 M_E and 10.8 +/- 0.6 M_E for planets b and c, respectively, and corresponding eccentricity estimates of 0.20 +/- 0.03 and 0.21 +/- 0.03. These high eccentricities raise questions about the formation origin of the system, and this motivated us to extend the observing baseline in an attempt to better constrain their values. We present a photodynamical analysis of 10 years of transit data that confirms the previous mass estimates (30.8 +/- 1.3 M_E and 11.1 +/- 0.4 M_E), but reduces the median eccentricities to 0.04 +/- 0.02 and 0.07 +/- 0.02 for b and c, respectively. These values are more consistent with standard formation models, but still involve nonzero free eccentricity. The previously reported high eccentricities appear to be due to a single transit for which measurements taken at twilight mimicked ingress. This resulted in a 12-minute error in the midtransit time. The data that covered 1.3 and 5 so-called super and resonant periods were used to match a Fourier analysis of the transit-timing variation signal with simple analytic expressions for the frequencies and amplitudes to obtain planet mass estimates within 2% of the median photodynamical values, regardless of the eccentricities. Theoretical details of the analysis are presented in a companion paper. Additionally, we identified a possible planet candidate situated exterior to the b-c pair. Finally, in contrast to a previous study, our internal structure modeling of K2-19 b yields a metal mass fraction that is consistent with core accretion.

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arXiv2025

Architecture of planetary systems with and without outer giant planets I. Inner planet detections around HD 23079, HD 196067, and HD 86226

Understanding the link between outer giant planets (OGPs) and inner light planets (ILPs) is key to understanding planetary system formation and architecture. The correlation between these two populations of planets is debated both theoretically -- different formation models predict either a correlation or an anticorrelation -- and observationally. Several recent attempts to constrain this correlation have yielded contradictory results, due to small-number statistics and heterogeneous samples. We present an ongoing long-term observational effort with CORALIE, HARPS, and ESPRESSO to probe the ILP occurrence in systems with and without OGP. In this first article of a series, we discuss how, from the design to the observations, we ensured the homogeneity of the samples, both in terms of stellar properties and observing strategy. We also present the first three detections of ILPs in our OGP host sample. We find a 8.3 mE planet at 5.75 d around HD 23079, a 10.4 mE planet at 4.6 d around HD 196067, and we confirm the 7.5 mE planet at 3.98 d around HD 86226. While a rigorous statistical analysis of our samples will be performed in subsequent studies, the relatively low number of detections in our sample seems to contradict previous studies that found a strong OGP-ILP correlation.

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arXiv2025

Three Hot Jupiters transiting K-dwarfs with a significant heavy element mass

Albeit at a lower frequency than around hotter stars, short-period gas giants around low-mass stars ($T_\mathrm{eff} < 4965$ K) do exist, despite predictions from planetary population synthesis models that such systems should be exceedingly rare. By combining data from TESS and ground-based follow-up observations, we seek to confirm and characterize giant planets transiting K dwarfs, particularly mid/late K dwarfs. Photometric data were obtained from the TESS mission, supplemented by ground-based imaging- and photometric observations, as well as high-resolution spectroscopic data from the CORALIE spectrograph. Radial velocity (RV) measurements were analyzed to confirm the presence of companions. We report the confirmation and characterization of three giants transiting mid-K dwarfs. Within the TOI-2969 system, a giant planet of $1.16\pm 0.04\,M_\mathrm{Jup}$ and a radius of $1.10 \pm 0.08\,R_\mathrm{Jup}$ revolves around its K3V host in 1.82 days. The system of TOI-2989 contains a $3.0 \pm 0.2\,M_\mathrm{Jup}$ giant with a radius of $1.12 \pm 0.05\,R_\mathrm{Jup}$, which orbits its K4V host in 3.12 days. The K4V TOI-5300 hosts a giant of $0.6 \pm 0.1\,M_\mathrm{Jup}$ with a radius of $0.88 \pm 0.08\,R_\mathrm{Jup}$ and an orbital period of 2.3 days. The equilibrium temperatures of the companions range from 1001 to 1186 K, classifying them as Hot Jupiters. However, they do not present radius inflation. The estimated heavy element masses in their interior, inferred from the mass, radius, and evolutionary models, are $90 \pm 30\,M_\oplus$, $114 \pm 30\,M_\oplus$, and $84 \pm 21\,M_\oplus$, respectively. The heavy element masses are significantly higher than most reported heavy elements for K-dwarf Hot Jupiters. These mass characterizations contribute to the poorly explored population of massive companions around low-mass stars.

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arXiv2025

CORALIE radial-velocity search for companions around evolved stars (CASCADES) IV: New planetary systems around HD 87816, HD 94890, and HD 102888 and an update on HD 121056

With around 200 detections of exoplanets around giant stars to date, our knowledge of the population of exoplanets orbiting evolved hosts more massive than the Sun remains limited. The CORALIE radial-velocity search for companions around evolved stars (CASCADES) was launched in 2006 with the aim of improving our understanding of the demographics of exoplanets around intermediate-mass stars, by studying them once they have evolved off the main sequence. We intend to refine the current sample of known exoplanets orbiting intermediate-mass (1.5 - 5 M$_\odot$) giant stars of spectral types G and early K. We searched for exoplanets orbiting the four stars HD 87816, HD 94890, HD 102888, and HD 121056. We used data obtained with the CORALIE spectrograph, mounted on the Leonhard Euler Swiss telescope located at La Silla Observatory in Chile. We gathered high-precision radial-velocity measurements over more than ten years for each of the aforementioned targets. We started by performing a search for periodic signals in the radial-velocity time series of the four targets by using periodograms. Following this, we fit for a Keplerian model using the significant peak with the highest power of the periodogram as the starting guess for the period. We then subtracted this model and repeated the procedure iteratively on the residuals until no significant peaks were found. Finally, to explore the posterior distribution of our models, the final solution was determined using a Markov chain Monte Carlo approach. We report the discovery of five new massive planets around HD 87816, HD 94890, and HD 102888 as well as the presence of a distant, potentially substellar, companion around HD 102888. We confirm the presence of a previously announced exoplanet orbiting the HD 121056 multi-object system with a period of 89 days and propose an update to the period of the outer companion.

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arXiv2022

Large Interferometer For Exoplanets (LIFE): I. Improved exoplanet detection yield estimates for a large mid-infrared space-interferometer mission

One of the long-term goals of exoplanet science is the atmospheric characterization of dozens of small exoplanets in order to understand their diversity and search for habitable worlds and potential biosignatures. Achieving this goal requires a space mission of sufficient scale. We seek to quantify the exoplanet detection performance of a space-based mid-infrared nulling interferometer that measures the thermal emission of exoplanets. For this, we have developed an instrument simulator that considers all major astrophysical noise sources and coupled it with Monte Carlo simulations of a synthetic exoplanet population around main-sequence stars within 20 pc. This allows us to quantify the number (and types) of exoplanets that our mission concept could detect over a certain time period. Two different scenarios to distribute the observing time among the stellar targets are discussed and different apertures sizes and wavelength ranges are considered. Within a 2.5-year initial search phase, an interferometer consisting of four 2 m apertures with a total instrument throughput of 5% covering a wavelength range between 4 and 18.5 $μ$m could detect up to ~550 exoplanets with radii between 0.5 and 6 R$_\oplus$ with an integrated SNR$\ge$7. At least ~160 of the detected exoplanets have radii $\le$1.5 R$_\oplus$. Depending on the observing scenario, ~25-45 rocky exoplanets (objects with radii between 0.5 and 1.5 $_{\oplus}$) orbiting within the empirical habitable zone (eHZ) of their host stars are among the detections. With an aperture size of 3.5 m, the total number of detections can increase to up to ~770, including ~60-80 rocky, eHZ planets. With 1 m aperture size, the maximum detection yield is ~315 exoplanets, including $\le$20 rocky, eHZ planets. In terms of predicted detection yield, such a mission can compete with large single-aperture reflected light missions. (abridged)

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