Olga Suarez

We report the confirmation and characterisation of two moderate-period sub-Jovian planets transiting the bright F-type star HD 148797 ( G = 9.4 mag, T _eff = 6441 ± 51 K). Using photometric time series from TESS and CHEOPS, we determined orbital periods of 42.1 d for HD 148797 b and 68.2 d for HD 148797 c, putting the period ratio very close to the golden mean at 1.619 and therefore near several strong harmonics, and we measured planetary radii of 8.25 ± 0.37 R _E and 8.37 ± 0.38 R _E , respectively. We detected significant anti-correlated transit-timing variations for both planets, which contain enough harmonic information to yield photodynamical masses of 39.3 _−8.5 ⁺¹³ M _E for HD 148797 b and 39.6 ± 9.3 M _E for HD 148797 c. The corresponding bulk densities, 0.39 ± 0.12 and 0.377 ± 0.084 g cm ⁻³ , place both planets among the low-density sub-Jovians of the Neptunian savanna. The architecture of HD 148797 is not unusual within this regime: we find that detected multi-system fractions in the savanna remain at ∼70–90%, and that most savanna multi-planet systems contain at least one adjacent planet pair with P _out / P _in < 3. This pattern suggests that savanna sub-Jovians are commonly found in dynamically cold systems, consistent with smoother migration pathways such as disk-driven migration rather than disruptive high-eccentricity tidal migration. As a bright, co-evolved system hosting two warm savanna sub-Jovians with similar radii and masses, HD 148797 is also a promising target for comparative atmospheric characterisation.

Long-period transiting planets are essential edge-cases for understanding exoplanet formation and evolution. Their detection is challenging due to the infrequent nature of their transits, making every observation of these objects very valuable. Our goal is to confirm and further characterise the long-period planetary candidate TOI-4409,b (initially identified by TESS) through additional observations using the Antarctica-based ASTEP telescope, supplemented with CHAT, OMES, LCOGT, and PEST light-curve data and radial-velocity (RV) measurements collected with the HARPS, FEROS, and PFS instruments. We jointly analysed the photometric data from eight TESS, four ASTEP, one CHAT, two OMES, four LCOGT, and one PEST light curve(s), and RV data from the HARPS, FEROS, and PFS instruments, covering observations from 2018 to 2024. TOI-4409,b is a bona fide puffy warm super-Neptune exoplanet with a planet radius of 7.44 ± 0.19,R_⊕, and a mass of 0.047 ± J ,(3σ upper limit <0.095,M_ J) orbiting a low-mass main-sequence star (effective temperature of 4928 ± 48, and a stellar radius of 0.720 ± 0.018, _⊙) with a period of 92.49179 ± 0.00010 days. The integration of various observational methods and consistent transit signals across multiple instruments confirms the planetary nature of TOI-4409,b. The combined transit, imaging, chromaticity, and RV evidence supports the confirmation of the planet. K R With a radius of 7.44 ± 0.19,R_⊕ and a low bulk density of 0.20 ± 0.07 -3 $, TOI-4409,b occupies a sparsely populated region of parameter space among warm, puffy super-Neptunes on long-period orbits. The detection of candidate transit timing variations with an ∼10-minute semi-amplitude hints at the presence of an additional body in the system. The favourable host-star brightness and extended transit duration ($∼7 hours) make TOI-4409,b a promising target for atmospheric characterisation with JWST and Ariel.

We present the analysis of five long-period TESS Objects of Interest (TOIs), , with orbital periods exceeding one month. Initially identified by the Transiting Exoplanet Survey Satellite (TESS), we extensively monitored these targets with the Antarctic Search for Transiting Exoplanets (ASTEP), supported by other facilities in the TESS Follow-up Observing Program (TFOP) network. all orbiting Sun-like stars These targets occupy a relatively underexplored region of the period-radius parameter space, offering valuable primordial probes for planetary formation and migration as warm planets better maintain their evolutionary fingerprints. To characterise these systems, we leveraged high-resolution speckle imaging to search for nearby stellar companions, and refine stellar parameters using both reconnaissance spectroscopy and spectral energy distribution (SED) fitting. We combined TESS photometry with high-precision ground-based observations from ASTEP, and when available, included additional photometry and radial velocity data. We applied statistical validation to assess the planetary nature of each candidate and used to jointly model the photometric and spectroscopic datasets. We validate the planetary nature of three TOIs, including the two warm Saturns TOI-4507,b (8.2, 104,d) and TOI-3457,b (10.0, 32.6,d), as well as the warm sub-Neptune TOI-707,b (2.4, eclipsing binaries, namely TOI-2404 and TOI-4404. 52.8,d). The remaining two candidates are most consistent with These results help populate the sparse regime of warm planets, which serve as key tracers of planetary evolution, and demonstrate ASTEP’s effectiveness as a ground-based follow-up instrument for long-period systems.

We identify two large-radius planets around the F-type star HD 114082 as the longest-period young transiting exoplanets known. From the first transit, detected by NASA’s Transiting Exoplanet Survey Satellite (TESS), and a second dip, spotted by the Next-Generation Transit Survey (NGTS), we predicted midtransit times for HD 114082 b (planet b). We pinpoint its orbit (period P _b = 225.5504 ± 0.0004 days) from a third transit captured with the ESA’s CHaracterising ExOplanet Satellite and the upgraded Antarctic Search for Transiting ExoPlanets telescope (ASTEP+), alongside orbit-discriminating observations. Another dimming partly covered by ASTEP+ completes the four-transit series. We support with dynamical evidence the planetary nature of a deeper transit detected with TESS and NGTS, identifying planet c. Additionally, we reexamine the debris disk, fitting its excess emission with two dust components. Fundamental stellar parameters are inferred from stellar evolution models, while a joint modeling of photometric and radial velocity time series yields the planetary parameters, with masses further constrained using an N-body code. For planet b, the semimajor axis a _b = 0.791 ± 0.008 au, eccentricity e _b ≈0, inclination i _b = 89 . ° 791 ±0.014, radius R _b = 1.046 ± 0.014 R _J , and 95% confidence upper limit on its mass M _95%,b = 1.6 M _J . For planet c, a _c = 0.99 − 0.04 + 0.03 au, e _c ≈0, i _c = 89 . ° 701 ±0.011, R _c = 1.36±0.03 R _J , and M _95%,c = 2.0 M _J (0.24 M _J if adding transit-timing-variation constraints). They seem to be moderate-to-low-mass giants in nearly resonant, coplanar, circular orbits that formed in situ, or beyond the snow line, and migrated inward, shaping the disk.

We present the combined JWST/NIRSpec/G395H and NIRISS/SOSS transmission spectrum of a warm mini-Neptune, TOI-1130 b (3.66 R _⊕ , 19.8 M _⊕ , and T _eq ∼ 825 K). It is part of a rare and unique multiplanet system, TOI-1130, which hosts an inner mini-Neptune and an outer hot Jupiter locked in a 2:1 mean motion resonance. From the transmission spectrum of TOI-1130 b we detect multiple molecules—H ₂ O (7.5 σ ), CO ₂ (3.3 σ ), and SO ₂ (3.6 σ ), as well as a tentative detection of CH ₄ (∼2 σ ). We find a strong optical slope in the NIRISS/SOSS spectrum, which is consistent with TESS and CHEOPS transit depth measurements. From equilibrium chemistry retrievals we measure the atmospheric metallicity ( log Z / Z ⊙ = 1 . 8 − 0.3 + 0.4 ) and C/O ratio (σ level confidence) and constrain the atmospheric mean molecular weight, μ = 5.5 − 0.8 + 1.3 amu. These constraints are consistent with self-consistent forward model grids. We detect no significant He I 1.083 μ m absorption signal and find a mass-loss rate upper limit of 10 ¹¹ g s ⁻¹ . The volatile-rich high mean molecular weight atmosphere of TOI-1130 b along with the “pebble-filtering” effect of the outer hot Jupiter supports the ex situ formation scenario beyond the water ice line and subsequent migration, coherent with its present orbital architecture. A volatile-rich formation scenario could also potentially explain the location of TOI-1130 b at the edge of the “radius cliff.” This result hints that the mini-Neptune population may not have a homogeneous formation history; rather, volatile-rich ex situ formation also contributes to its population.

Studying planetary interactions in exoplanet systems informs theories of planet formation and evolution, providing essential context for understanding our own solar system. We combine spectroscopy, transit photometry, transit timing variations, and astrometry to characterize the TOI-201 system. The cotransiting system consists of a super-Earth, warm Jupiter, and massive companion at 5.8-, 53-, and 2900-day orbital periods, respectively. We perform dynamical simulations to study the past and future of the system. von-Zeipel-Kozai-Lidov oscillations emerge as the most plausible scenario to explain the outer companion’s high orbital eccentricity, with planet-planet scattering a possible but less likely contender. Because of nonzero mutual inclinations between the planets, the system is visibly evolving on very short timescales, with the current cotransiting configuration ending in 200 years.

TOI-1232 is a G dwarf star with a mass of 1.0 6 − 0.06 + 0.07 M ⊙ , a radius of 1.07 ± 0.05 R _⊙ , and a slightly higher metallicity than solar of Fe/H = 0.18 ± 0.05. The star hosts a transiting warm Jovian-mass planet, TOI-1232 b, with an orbital period of P b = 14.25 6 − 0.001 + 0.001 days, identified with data from multiple sectors of the TESS space telescope. The TESS light curve of TOI-1232 is complex, as it is contaminated by a background eclipsing binary with a period of 1.37 days. TOI-1232 b was firmly confirmed by ground-based transit follow-up campaigns from the Las Cumbres, Hazelwood, Brierfield, and ASTEP observatories. Additionally, the TESS transits of TOI-1232 b exhibit strong transit-timing variations (TTVs) with a superperiod of 235.5 ± 0.7 days and a semiamplitude of 27 minutes. Radial velocity (RV) follow-up with the FEROS spectrograph confirms the planetary nature of the transiting candidate, while a self-consistent N -body analysis of RVs and TTVs pinpoints the presence of a second outer Saturn-mass companion, TOI-1232 c with a period of P c = 30.35 6 − 0.012 + 0.010 days. The TOI-1232 warm-giant system is particularly important due to the evidence of two massive planets that reside near the 2:1 commensurability but are not locked in a mean-motion resonance. Thanks to TESS, we have revealed a handful of these rare systems. Hence, TOI-1232 is an important addition to understanding the formation and dynamical evolution of such compact, massive, warm giant planets.

We report the discovery of TOI-4507 b, a transiting sub-Saturn with a density −3 on a 105 days prograde orbit around a 700 Myr old F star. The transits were detected using data from TESS as well as the Antarctic telescope ASTEP. A joint analysis of the light curves and radial velocities from HARPS, FEROS, and CORALIE confirmed the planetary nature of the signal, by limiting the mass to be below 20 M _⊕ at 95% confidence. The radial velocities also exhibit the Rossiter–McLaughlin effect and imply that the planet orbits the star in a prograde orbit with a sky-projected obliquity λ = − 15 − 44 + 50 ° (∣ λ ∣ < 80° at 3 σ ). With these characteristics, TOI-4507 is one of the longest-period systems for which the stellar obliquity has been measured, and the planet is among the longest-period and youngest “superpuff” planets yet discovered.

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.