arXiv subjects

S. Udry

Publications and source records attributed to S. Udry.

At least 37 records · Page 2Linked to original sources

arXiv2025

TOI-7510: A solar-analog system of three transiting giant planets near a Laplace resonance chain

We report the confirmation and initial characterization of a compact and dynamically rich multiple giant planet system orbiting the solar analog TOI-7510. The system was recently identified as a candidate two-planet system in a machine-learning search of the TESS light curves. Using TESS data and photometric follow-up observations with ASTEP, CHEOPS, and EulerCam, we show that one transit was initially misattributed and that the system consists of three transiting giant planets with orbital periods of 11.5, 22.6, and 48.9 days. The planets have radii of 0.65, 0.96, and 0.94 R_J, making them the largest known trio of transiting planets. The system architecture lies near a 4:2:1 mean motion resonant chain, inducing large transit timing variations for all three planets. Photodynamical modeling gives mass estimates of 0.057, 0.41, and 0.60 M_J and favors low eccentricities and mutual inclinations. TOI-7510 is an interesting system for investigating the dynamical interactions and formation histories of compact systems of giant planets.

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arXiv2025

HARPS-N, TESS, and CHEOPS discover a transiting sub-Neptune and two outer companions around the bright solar analogue HD 85426

We provide a detailed characterisation of the planetary system orbiting HD 85426 (TOI-1774). This bright G-type star ($M_{\ast}$: 0.99 $\text{M}_{\odot}$; $R_{\ast}$: 1.13 $\text{R}_{\odot}$; age: 7.4 Gyr; V mag: 8.25) hosts a transiting sub-Neptune, HD 85426 b, with an orbital period of 16.71 days and a blackbody equilibrium temperature of $824^{+11}_{-11}$ K. By jointly analysing HARPS-N RVs, TESS, and CHEOPS photometric data and using two different stellar activity mitigation techniques, we constrain planet b's mass to $6.0^{+1.5}_{-1.6}$ $\text{M}_{\oplus}$ and $8.5^{+1.3}_{-1.4} $ $\text{M}_{\oplus}$, depending on the mitigation technique. We investigate the dependence of these results on the priors, data selection, and inclusion of other Keplerians in the modelling. Using this approach, we identify the presence of two non-transiting planetary companions with minimum masses near 10 $\text{M}_{\oplus}$ and orbital periods of 35.7 and 89 days. Additionally, we reject the initial hypothesis that the 35.7-day periodic signal was due to stellar activity. We also determine HD 85426 b's radius to be $2.78^{+0.05}_{-0.04}$ $\text{R}_{\oplus}$ and compute a transmission spectroscopy metric in the range of 82 to 115, making this planet a highly valuable target for atmospheric characterisation.

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arXiv2025

Transit Timing Variations in HIP 41378: CHEOPS and TESS confirm a non-transiting sixth planet in the system

In multiple-planet systems, gravitational interactions of exoplanets could lead to transit timing variations (TTVs), whose amplitude becomes significantly enhanced when planets are in or near mean-motion resonances (MMRs). In cases where both TTVs and radial velocity (RV) measurements are available, combined analysis can break degeneracies and provide robust planetary and system characterization, even detecting non-transiting planets. In this context, HIP 41378 hosts five confirmed transiting planets with periods ranging from 15 to over 542 days, providing a unique dynamical laboratory for investigating wide multi-planet systems analogous to the Solar System. In this study, we present an intensive space-based photometric follow-up of HIP 41378, combining 15 new CHEOPS observations with eight TESS sectors, alongside data from K2, Spitzer, HST, and HARPS. We dynamically modeled the TTVs and RV signals of the two inner sub-Neptunes via N-body integration. These planets, HIP 41378 b ($P_{b}$ = 15.57 days) and HIP 41378 c ($P_{c}$ = 31.71 days), are close to ($Δ\sim1.8$ %) a 2:1 period commensurability. We report a clear detection of TTVs with amplitudes of 20 mins for planet b and greater than 3 hrs for planet c. We dynamically confirm the planetary nature of HIP 41378 g, a non-transiting planet with a period of about 64 days and a mass of about 7 $M_{\oplus}$, close to a 2:1 commensurability with planet c, suggesting a possible MMR chain in the inner system. Our precise determination of the masses, eccentricities, and radii of HIP 41378 b and c enabled us to investigate their possible volatile-rich compositions. Finally, by leveraging on the last TESS sectors we constrained the period of HIP 41378 d to three possible aliases ($P_{d} =$ 278, 371, and 1113 days) suggesting that the system could be placed in a double quasi resonant chain, highlighting its complex dynamical architecture.

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arXiv2025

A Decade of Solar High-Fidelity Spectroscopy and Precise Radial Velocities from HARPS-N

We recently released 10 years of HARPS-N solar telescope and the goal of this manuscript is to present the different optimisations made to the data reduction, to describe data curation, and to perform some analyses that demonstrate the extreme RV precision of those data. By analysing all the HARPS-N wavelength solutions over 13 years, we bring to light instrumental systematics at the 1 m/s level. After correction, we demonstrate a peak-to-peak precision on the HARPS-N wavelength solution better than 0.75 m/s over 13 years. We then carefully curate the decade of HARPS-N re-reduced solar observations by rejecting 30% of the data affected either by clouds, bad atmospheric conditions or well-understood instrumental systematics. Finally, we correct the curated data for spurious sub-m/s RV effects caused by erroneous instrumental drift measurements and by changes in the spectral blaze function over time. After curation and correction, a total of 109,466 HARPS-N solar spectra and respective RVs over a decade are available. The median photon-noise precision of the RV data is 0.28 m/s and, on daily timescales, the median RV rms is 0.49 m/s, similar to the level imposed by stellar granulation signals. On 10-year timescales, the large RV rms of 2.95 m/s results from the RV signature of the Sun's magnetic cycle. When modelling this long-term effect using the Magnesium II activity index, we demonstrate a long-term RV precision of 0.41 m/s. We also analysed contemporaneous HARPS-N and NEID solar RVs and found the data from both instruments to be of similar quality and precision, with an overall RV differece rms of 0.79 m/s. This decade of high-cadence HARPS-N solar observations with short- and long-term precision below 1 m/s represents a crucial dataset to further understand stellar activity signals in solar-type stars , and to advance other science cases requiring such an extreme precision.

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arXiv2025

TOI-283 b: A transiting mini-Neptune in a 17.6-day orbit discovered with TESS and ESPRESSO

Super-Earths and mini-Neptunes are missing from our Solar System, yet they appear to be the most abundant planetary types in our Galaxy. A detailed characterization of key planets within this population is important for understanding the formation mechanisms of rocky and gas giant planets and the diversity of planetary interior structures. In 2019, NASA's TESS satellite found a transiting planet candidate in a 17.6-day orbit around the star TOI-283. We started radial velocity (RV) follow-up observations with ESPRESSO to obtain a mass measurement. Mass and radius are measurements critical for planetary classification and internal composition modeling. We used ESPRESSO spectra to derive the stellar parameters of the planet candidate host star TOI-283. We then performed a joint analysis of the photometric and RV data of this star, using Gaussian processes to model the systematic noise present in both datasets. We find that the host is a bright K-type star ($d = 82.4$ pc, $\mathrm{T}_\mathrm{eff} = 5213 \pm 70$ K, $V = 10.4$ mag) with a mass and radius of $\mathrm{M}_\star = 0.80 \pm 0.01\; \mathrm{M}_\odot$ and $\mathrm{R}_\star = 0.85 \pm 0.03\; \mathrm{R}_\odot$. The planet has an orbital period of $P = 17.617$ days, a size of $\mathrm{R}_\mathrm{p} = 2.34 \pm 0.09\; \mathrm{R}_\oplus$, and a mass of $\mathrm{M}_\mathrm{p} = 6.54 \pm 2.04\; \mathrm{M}_\oplus$. With an equilibrium temperature of $\sim$600 K and a bulk density of $ρ_\mathrm{p} = 2.81 \pm 0.93$ g cm$^{-3}$, this planet is positioned in the mass-radius diagram where planetary models predict H$_2$O- and H/He-rich envelopes. The ESPRESSO RV data also reveal a long-term trend that is probably related to the star's activity cycle. Further RV observations are required to confirm whether this signal originates from stellar activity or another planetary body in the system.

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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

Detection and characterisation of a 106-day transiting Jupiter : TOI-2449 b / NGTS-36 b

Only a handful of transiting giant exoplanets with orbital periods longer than 100 days are known. These warm exoplanets are valuable objects as their radius and mass can be measured leading to an in-depth characterisation of the planet's properties. Thanks to low levels of stellar irradiation and large orbital distances, the atmospheric properties and orbital parameters of warm exoplanets remain relatively unaltered by their host star, giving new insights into planetary formation and evolution. We aim at extending the sample of warm giant exoplanets with precise radii and masses. Our goal is to identify suitable candidates in the Transiting Exoplanet Survey Satellite (TESS) data and perform follow-up observations with ground-based instruments. We use the Next Generation Transit Survey (NGTS) to detect additional transits of planetary candidates in order to pinpoint their orbital period. We also monitored the target with several high-resolution spectrographs to measure the planetary mass and eccentricity. We report the discovery of a 106-day period Jupiter-sized planet around the G-type star TOI-2449 / NGTS-36. We jointly modelled the photometric and radial velocity data and find that the planet has a mass of 0.70 Mj and a radius of 1.002 Rj. The planetary orbit has a semi-major axis of 0.449 au and is slightly eccentric. We detect an additional 3-year signal in the radial velocity data likely due to the stellar magnetic cycle. Based on the planetary evolution models considered here, we find that TOI-2449 b / NGTS-36 b contains 11 Me of heavy elements and has a marginal planet-to-star metal enrichment of 3.3. Assuming a Jupiter-like Bond albedo, TOI-2449 b / NGTS-36 b has an equilibrium temperature of 400 K and is a good target for understanding nitrogen chemistry in cooler atmospheres.

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arXiv2025

The star HIP 41378 potentially misaligned with its cohort of long-period planets

The obliquity between the stellar spin axis and the planetary orbit, detected via the Rossiter-McLaughlin (RM) effect, is a tracer of the formation history of planetary systems. While obliquity measurements have been extensively applied to hot Jupiters and short-period planets, they remain rare for cold and long-period planets due to observational challenges, particularly their long transit durations. We report the detection of the RM effect for the 19-hour-long transit of HIP 41378 f, a temperate giant planet on a 542-day orbit, observed through a worldwide spectroscopic campaign. We measure a slight projected obliquity of 21 $\pm$ 8 degrees and a significant 3D spin-orbit angle of 52 $\pm$ 6 degrees, based on the measurement of the stellar rotation period. HIP 41378 f is part of a 5-transiting planetary system with planets close to mean motion resonances. The observed misalignment likely reflects a primordial tilt of the stellar spin axis relative to the protoplanetary disk, rather than dynamical interactions. HIP 41378 f is the first non-eccentric long-period (P>100 days) planet observed with the RM effect, opening new constraints on planetary formation theories. This observation should motivate the exploration of planetary obliquities across a longer range of orbital distances through international collaboration.

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arXiv2025

Improved characterization of the TOI-2141 system: a dense sub-Neptune with non-transiting inner and outer companions

We aim to refine the fundamental parameters of the TOI-2141 planetary system, which includes a transiting sub-Neptune orbiting a Sun-like star in a relatively long orbit of 18.26 days, by combining new photometric and spectroscopic observations. We analyze new space-based photometry from TESS and CHEOPS as well as 61 radial velocity measurements from HARPS-N. We perform individual and joint photometric and RV analyses using several modeling tools within a Bayesian model comparison framework. We refine the radius and mass of the transiting planet TOI-2141 b to 3.15 $\pm$ 0.04 $R_\oplus$ and 20.1 $\pm$ 1.6 $M_\oplus$, respectively, five and two times more precise than the previously reported values. Our radial velocity analysis reveals two additional non-transiting companions with orbital periods of 5.46 and 60.45 days. Despite the innermost planet's high geometric transit probability, we find no evidence for transits in the photometric data. The bulk properties of TOI-2141 b suggest a significant volatile envelope atop an Earth-like core, with modeling indicating a hydrogen-rich atmosphere that may have experienced mild photoevaporation over the system's history. Planets b and c must exhibit a modest mutual inclination of at least 2.4 degrees.

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arXiv2025

TOI-2322: two transiting rocky planets close to the stellar rotation period and its first harmonic

Context. Active regions on the stellar surface can induce quasi-periodic radial velocity (RV) variations that can mimic planets and mask true planetary signals. These spurious signals can be problematic for RV surveys such as those carried out by the ESPRESSO consortium. Aims. Using ESPRESSO and HARPS RVs and activity indicators, we aim to confirm and characterize two candidate transiting planets from TESS orbiting a K4 star with strong activity signals. Methods. From the ESPRESSO FWHM, TESS photometry, and ASAS-SN photometry, we measure a stellar rotation period of 21.28 $\pm$ 0.08 d. We jointly model the TESS photometry, ESPRESSO and HARPS RVs, and activity indicators, applying a multivariate Gaussian Process (GP) framework to the spectroscopic data. Results. We are able to disentangle the planetary and activity components, finding that TOI-2322 b has a $11.307170^{+0.000085}_{-0.000079}$ d period, close to the first harmonic of the rotation period, a $\leq 2.03 M_\oplus$ mass upper limit and a $0.994^{+0.057}_{-0.059}$ $\mathrm{R_\oplus}$ radius. TOI-2322 c orbits close to the stellar rotation period, with a $20.225528^{+0.000039}_{-0.000044}$ d period; it has a $18.10^{+4.34}_{-5.36}$ $\mathrm{M_\oplus}$ mass and a $1.874^{+0.066}_{-0.057}$ $\mathrm{R_\oplus}$ radius. Conclusions. The multivariate GP framework is crucial to separating the stellar and planetary signals, significantly outperforming a one-dimensional GP. Likewise, the transit data is fundamental to constraining the periods and epochs, enabling the retrieval of the planetary signals in the RVs. The internal structure of TOI-2322 c is very similar to that of Earth, making it one of the most massive planets with an Earth-like composition known.

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arXiv2025

Discovery of a multi-planetary system orbiting the aged Sun-like star HD 224018

In 2016, Kepler/K2 detected a system of two sub-Neptunes transiting the star HD 224018, one of them showing a mono-transit event. In 2017, we began a spectroscopic follow-up with HARPS-N to measure the dynamical masses of the planets using radial velocities, and collected additional transit observations using CHEOPS. We measured the fundamental physical parameters of the host star, which is an ``old Sun'' analogue. We analysed radial velocities and photometric time series, also including data by TESS, to provide precise ephemerides, radii, masses, and bulk densities of the two planets, and possibly modeling their internal structure and composition. The system turned out to be more crowded than shown by K2. Radial velocities revealed the presence of two additional bodies: a candidate cold companion on an eccentric orbit with a minimum mass nearly half that of Jupiter (eccentricity $0.60^{+0.07}_{-0.08}$; semi-major axis 8.6$^{+1.5}_{-1.6}$ au), and an innermost super-Earth (orbital period 10.6413$\pm$0.0028 d; mass 4.1$\pm$0.8 Me) for which we discovered previously undetected transit events in K2 photometry. TESS revealed a second transit of one of the two companions originally observed by K2. This allowed us to constrain its orbital period to a grid of values, the most likely being $\sim$138 days, which would imply a mass less than 9 Me, at a 3$σ$ significance level. Given the level of precision of our measurements, we were able to constrain the internal structure and composition of the second-most distant planet from the host star, a warm sub-Neptune with a bulk density of 3.9$\pm$0.5 g/cm$^{3}$. HD 224018 hosts three close-in transiting planets in the super-Earth-to-sub-Neptune regime, and a candidate cold and eccentric massive companion. Additional follow-up is needed to better characterise the physical properties of the planets and their architecture.

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arXiv2025

Characterizing planetary systems with SPIRou: Detection of a sub-Neptune in a 6-day period orbit around the M dwarf Gl 410

The search for exoplanets around nearby M dwarfs represents a crucial milestone in the census of planetary systems in the vicinity of our Solar System. Since 2018 our team is carrying a radial-velocity blind search program for planets around nearby M dwarfs with the near-IR spectro-polarimeter and velocimeter SPIRou at the CFHT and the optical velocimeter SOPHIE at the OHP in France. Here we present our results on Gl 410, a 0.55 Msun 480+-150 Myr old active M dwarf distant 12 pc. We used the line-by-line (LBL) technique to measure the RVs with SPIRou and the template matching method with SOPHIE. Three different methods were employed, two based on principal component analysis (PCA), to clean the SPIRou RVs for systematics. We applied Gaussian processes (GP) modeling to correct the SOPHIE RVs for stellar activity. The l1 and apodize sine periodogram analysis was used to search for planetary signals in the SPIRou data taking into account activity indicators. We analyzed TESS data and searched for planetary transits. We report the detection of a M sin(i)=8.4+-1.3 Mearth sub-Neptune planet at a period of 6.020+-0.004 days in circular orbit with SPIRou. The same signal, although with lower significance, was also retrieved in the SOPHIE RV data after correction for activity using a GP trained on SPIRou's longitudinal magnetic field (Bl) measurements. The TESS data indicate that the planet is not transiting. Within the SPIRou wPCA RVs, we find tentative evidence for two additional planetary signals at 2.99 and 18.7 days. In conclusion, infrared RVs are a powerful method to detect extrasolar planets around active M dwarfs. Care should be taken however to correct/filter systematics generated by residuals of the telluric correction or small structures in the detector plane. The LBL technique combined with PCA offers a promising way to reach this objective. Further monitoring of Gl 410 is necessary.

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arXiv2025

The CHEOPS view of HD 95338b: refined transit parameters, and a search for exomoons

Despite the ever-increasing number of known exoplanets, no uncontested detections have been made of their satellites, known as exomoons. The quest to find exomoons is at the forefront of exoplanetary sciences. Certain space-born instruments are thought to be suitable for this purpose. We show the progress made with the CHaracterizing ExOPlanets Satellite (CHEOPS) in this field using the HD 95338 planetary system. We present a novel methodology as an important step in the quest to find exomoons. We utilize ground-based spectroscopic data in combination with Gaia observations to obtain precise stellar parameters. These are then used as input in the analysis of the planetary transits observed by CHEOPS and the Transiting Exoplanet Survey Satellite (TESS). In addition, we search for the signs of satellites primarily in the form of additional transits in the Hill sphere of the eccentric Neptune-sized planet HD 95338b in a sequential approach based on four CHEOPS visits. We also briefly explore the transit timing variations of the planet. We present refined stellar and planetary parameters, narrowing down the uncertainty on the planet-to-star radius ratio by a factor of $10$. We also pin down the ephemeris of HD 95338b. Using injection/retrieval tests, we show that a $5 σ$ detection of an exomoon would be possible at $R_{\rm Moon} = 0.8$~$R_\oplus$ with the methodology presented here. We exclude the transit of an exomoon in the system with $R_{\rm Moon} \approx 0.6$~$R_\oplus$ at the $1σ$ level. The algorithm used for finding the transit-like event can be used as a baseline for other similar targets, observed by CHEOPS or other missions.

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arXiv2025

A comprehensive study on radial velocity signals using ESPRESSO: Pushing precision to the 10 cm/s level

We analyse ESPRESSO data for the stars HD10700, HD20794, HD102365, and HD304636 acquired via its Guaranteed Time Observations (GTO) programme. We characterise the stars' radial velocity (RV) signals down to a precision of 10 cm/s on timescales ranging from minutes to planetary periods falling within the host's habitable zone (HZ). We study the RV signature of pulsation, granulation, and stellar activity, inferring the potential presence of planets around these stars. Thus, we outline the population of planets that while undetectable remain compatible with the available data. A simple model of stellar pulsations successfully reproduced the intra-night RV scatter of HD10700 down to a few cm/s. For HD102365 and HD20794, an additional source of scatter at the level of several 10 cm/s remains necessary to explain the data. A kima analysis was used to evaluate the number of planets supported by the nightly averaged time series of each of HD10700, HD102365, and HD304636, under the assumption that a quasi-periodic Gaussian process (GP) regression is able to model the activity signal. While a frequency analysis of HD10700 RVs is able to identify a periodic signal at 20d, when it is modelled along with the activity signal the signal is formally non-significant. ESPRESSO data on their own do not provide conclusive evidence for the existence of planets around these three stars. ESPRESSO is shown to reach an on-sky RV precision of better than 10 cm/s on short timescales (<1h) and of 40 cm/s over 3.5 yr. A subdivision of the datasets showcases a precision reaching 20-30 cm/s over one year. These results impose stringent constraints on the impact of granulation mechanisms on RV. In spite of no detections, our analysis of HD10700 RVs demonstrates a sensitivity to planets with a mass of 1.7M$_{\oplus}$ for periods of up to 100 d, and a mass of 2-5M$_{\oplus}$ for the star's HZ. (abridged)

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arXiv2025

The KELT-7b atmospheric thermal-inversion conundrum revisited with CHEOPS, TESS, and additional data

Ultrahot Jupiters are predicted to show inverted temperature-pressure (T-P) profiles in the presence of optical absorbers such as TiO and VO. An inverted T-P profile of KELT-7b was recently detected, in line with these predictions, but such diagnoses are known to be model-dependent. We used CHEOPS, TESS, and literature data to characterize the atmosphere of KELT-7b, reassess its T-P profile, measure its albedo, and search for distortions in its CHEOPS transit light curve due to stellar rotation. We jointly fitted CHEOPS and TESS data to measure the occultation depths and modeled CHEOPS transits including gravity darkening. Emission and transmission retrievals were performed, and the albedo was calculated in the CHEOPS and TESS passbands. Thermochemical-equilibrium retrievals yield a non-inverted T-P profile, while free-chemistry retrievals yield an inverted profile with likely unphysical TiO/VO abundances. A 3D GCM supports a TiO-driven inversion. We report a low geometric albedo of $A_\mathrm{g} = 0.05 \pm 0.06$, consistent with inefficient heat redistribution and supported by a GCM with magnetic drag. CHEOPS data provide no constraint on the sky-projected orbital obliquity. Retrieval results strongly depend on the chemical framework. Free-chemistry fits are better but risk unphysical solutions for ultrahot Jupiters. We applied a coherent stellar variability correction to CHEOPS and TESS data; future observations would benefit from similar treatment.

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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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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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