arXiv subjects

K. A. Collins

Publications and source records attributed to K. A. Collins.

At least 19 recordsLinked to original sources

arXiv2026

The TASSIE Program. II: Three Close-In Companions Orbiting Sun-Like Stars

We present three southern transiting giant planet candidates alerted by the Transiting Exoplanet Survey Satellite (TESS) mission and investigated at the University of Tasmania Greenhill Observatory (UTGO). The candidate planets are orbiting thin disk G-dwarf main-sequence stars with roughly solar metallicity, possessing orbital periods between 2.9 - 3.3 days and radii of 1.1 - 1.3 $R_{J}$. We performed ground-based follow-up photometry primarily with the UTGO Harlingten 50 cm, then gathered reconnaissance spectra, high angular resolution imaging and high-precision radial velocities to rule out false positive scenarios. We confirmed that two of these systems host true exoplanets and constrained their masses. TOI-3053b is a typical hot Jupiter, with $M_{3053b} = 0.85 \pm 0.12$ M$_{J}$ and a bulk density of $\rho_{3053b} = 0.64 \pm 0.10$ g cm$^{-3}$. TOI-3278b / HATS-78b is a hot Saturn-mass planet ($M_{3278b} = 0.30 \pm 0.07$ $M_{J}$) with a highly inflated atmosphere and a low density of $\rho_{3278b} = 0.21 \pm 0.05$ g cm$^{-3}$. The other candidate (TOI-3272.01) remains unconfirmed, but appears consistent with being a hot Jupiter. TOI-3272.01 is notable as a candidate planet orbiting a potentially young to intermediate age star, with a rotational analysis indicating an age estimate of $T_{3272} = 1.1 \pm 0.2$ Gyr. These systems add to a growing sample of hot giant planets from TESS that may provide constraints on the migration pathways and radius inflation of the broader close-in exoplanet population.

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arXiv2026

CAFE follow-up of TESS hot Jupiter candidates left behind: I. Five newly confirmed planets and a false positive

Hot Jupiters are key targets for understanding planet formation, migration, and atmospheres. Yet, most ground-based follow-up resources for the TESS mission are focused on confirming low-mass planet candidates, leaving many giant planets without mass determinations or definitive confirmation. We use the \cafe{} spectrograph at Calar Alto Observatory to monitor the radial velocity of stars hosting hot-Jupiter candidates that have received little follow-up, aiming to confirm their planetary nature. We present results for seven candidates. We monitored the radial velocity of TOI-603, TOI-1137, TOI-1837, TOI-2114, TOI-4492, TOI-5806, and TOI-5811, jointly modeling the CAFE radial velocities and TESS photometry to determine the nature and properties of the transiting objects. We confirm five new planets: TOI-603 b ($33.0^{+6.5}_{-6.2}$ M$_{\oplus}$, $16.2$ d), TOI-2114 b ($1.01^{+0.14}_{-0.12}$ M$_{\rm Jup}$, $6.2$ d), TOI-4492 b ($5.92^{+0.67}_{-0.64}$ M$_{\rm Jup}$, $4.4$ d), TOI-5806 b ($2.77^{+0.34}_{-0.32}$ M$_{\rm Jup}$, $3.2$ d), and TOI-5811 B b ($0.81^{+0.11}_{-0.10}$ M$_{\rm Jup}$, $6.3$ d). TOI-603 b lies in the "Neptune savanna", whereas the other four are hot Jupiters orbiting slightly evolved stars. We find TOI-5811.01 to be a planet transiting the nearby bound companion TOI-5811 B (hence TOI-5811 B b), and identify a stellar companion to TOI-5806 at a projected separation of 248 au, making both S-type planetary systems. TOI-1837.01 is an eclipsing binary, while TOI-1137.01 remains inconclusive. The five confirmed planets orbit bright stars (${\rm G}=8.6-10.2$~mag), and four are excellent targets for atmospheric studies, with transmission spectroscopy metrics above 90. These results highlight the importance of intensive follow-up observations to establish the nature of transiting planet candidates.

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arXiv2026

The GAPS programme at TNG: LXXVI. TOI-1533: a compact system hosting a super-Neptune-mass pair with disparate radii

The present-day architecture of planetary systems contains information about their formation and migration histories. The origin of hot Jupiters (HJs, P $\lesssim$ 10 d, $R_{\rm p} > 8 R_\oplus$) has long been a matter of debate. While most of them are found to be ``lonely'', there is a rare population of HJs hosting small companions on inner orbits (eight known as of May 2026). Their peculiar architecture suggests a gentle disc-migration mechanism. In this study, we present the discovery and characterisation of the multi-planet system TOI-1533, comprising an inner sub-Neptune (TOI-1533 b, $P_{\rm orb} = 3.63$ d, $R_{\rm p} = 3.15 R_\oplus$) and an outer hot giant planet (TOI-1533 c, $P_{\rm orb} = 8.06$ d, $R_{\rm p} > 7.5 R_\oplus$) with substantial H/He by mass ($\rho_{\rm p} < 0.48$ g cm$^{-3}$), both transiting an active K-dwarf star ($T_{\rm eff} \approx$ 5130 K; $V$ (mag) $\approx$ 11). Our joint modelling of stellar activity and planetary signals from radial velocities (HARPS-N) and transits (TESS) allows us to detect their Keplerian signals (approximately $10~\sigma$) and to isolate the stellar modulation. The inclusion of simultaneous photometry in the multi-dimensional Gaussian processes formalism was a fundamental addition to the spectroscopic activity indicators, enabling the disentanglement of stellar activity from planetary signals. The mass ratio of the two confirmed planets ($M_{\rm b} / M_{\rm c}$ about 0.8), together with the super-Neptune mass of the large outer companion ($M_{\rm c} \approx 40 M_\oplus$), makes this system unusual compared to the other few HJs with low-mass inner companions.

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arXiv2026

TOI-159 b: an eccentric hot-Jupiter planet around a young, pulsating $\gamma$ Doradus star

Fast-rotating hot stars are challenging targets for exoplanet searches due to rotational broadening and stellar variability. Moreover, hot stars often exhibit pulsations, an additional source of scatter in both photometric and spectroscopic series. Because of these challenges, such stars remain a relatively unexplored environment for planetary architecture and evolution studies. In this study, we present the confirmation and preliminary atmospheric characterisation of a giant planet orbiting a young ($\approx$ 150 Myr), pulsating $\gamma$ Doradus star. TOI-159 b ($P_{\rm orb} \simeq 3.7$ d, $R_{\rm p} \simeq 1.6~R_{\rm J}$, $M_{\rm p} \simeq 3.5 M_{\rm J}$) is an S-type planet in a close binary system and is the hottest ($T_{\rm eq} \simeq 1900$ K) hot Jupiter with a significant eccentricity ($e = 0.24 \pm 0.04$) ever detected. Our joint modelling of radial velocities (HARPS and CORALIE), transits (\textit{TESS}), and spectro-photometry (IMACS) allows us to detect its Keplerian signal at high significance ($13 \sigma$), place strong constraints on its eccentricity ($6 \sigma$), disentangle the stellar rotational modulation and pulsation periods, and generate a low-resolution transmission spectrum, on which we conduct an exploratory analysis to constrain the presence of a planetary atmosphere using combined star-planet retrievals. Whilst our spectrum appears to display some modulation, the data is too coarse to allow for any conclusive detections at this stage. Higher-resolution observations are needed to confirm or refute these features and, if genuine, determine whether they originate from contamination from the star or a planetary atmosphere.

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arXiv2026

A gem system with a lava world and a habitable zone sub-Neptune orbiting TOI-1752

The Transiting Exoplanet Survey Satellite (TESS) has delivered a large number of transiting planet candidates around nearby stars by identifying periodic decreases in stellar brightness. Establishing the planetary nature of these signals and determining their fundamental properties is a necessary step toward detailed studies of their internal structure, atmospheres, and formation pathways. In this work, we investigate the planetary nature of the TOI-1752 system (M1 V, $103.02\pm0.34$ pc), which hosts two TESS candidates: TOI-1752 b, a short-period object consistent with a lava-world scenario, and TOI-1752 c, a sub-Neptune-size planet candidate located in the optimistic habitable zone. We obtained ground-based multi-color photometric follow-up observations of TOI-1752, which we combined with TESS photometry to assess the nature of both signals. We performed a formal statistical validation using the TRICERATOPS framework, while independently vetting the candidates with the neural-network-based classifier WATSON-Net, which provides a machine-learning assessment of their planetary likelihood based on light-curve morphology, centroid diagnostics, and auxiliary vetting features. We validate TOI-1752 b as a bona fide planet with a radius of $1.69\pm0.07 R_{\oplus}$ and an orbital period of $0.935186^{+0.000001}_{-0.000002}$ days, and TOI-1752 c with a radius of $2.29^{+0.13}_{-0.14} R_{\oplus}$ and an orbital period of $32.7144\pm0.0004$ days. The combined analysis confirms TOI-1752 as a new planetary system, places TOI-1752 c within the optimistic habitable zone of its host star, and identifies TOI-1752 b as a promising target for atmospheric characterization, with an estimated emission spectroscopy metric (ESM) of up to $\sim8$.

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arXiv2026

TOI-4616 b: a benchmark Earth-sized planet transiting a nearby M4 dwarf

Rocky exoplanets are particularly abundant around M-type stars. Their small radii and low luminosities provide favourable conditions for detecting transiting terrestrial planets and probing their atmospheric properties. We report the discovery and statistical validation of TOI-4616 b, an Earth-sized planet transiting a nearby mid-M dwarf observed by the Transiting Exoplanet Survey Satellite (TESS). We confirm the planetary nature of the signal and determine the system parameters by combining TESS photometry with ground-based multi-band transit observations, high-resolution imaging, and optical and near-infrared spectroscopy. The host star lies at a distance of 28.10 +(-) 0.07 pc and has a radius of 0.1889 +(-)0.0096 solar radii, a mass of 0.1881 +(-) 0.0094 solar masses, and an effective temperature of 3150 +(-) 75 K. TOI-4616 b has a radius of 1.22 Earth radii and an orbital period of 1.55 days. The planet receives an incident flux of approximately 40 times that of Earth, corresponding to an equilibrium temperature of about 525 K. This places TOI-4616 b in a regime intermediate between Earth-sized planets orbiting early M dwarfs and those around ultra-cool hosts. Statistical validation with the TRICERATOPS framework, supported by high-resolution imaging and chromatic transit constraints, yields a false-positive probability of 0.0135, below the recommended validation threshold of 0.015, confirming TOI-4616 b as a validated planet. Owing to its proximity to Earth, well-constrained stellar properties, and extensive multi-band follow-up, TOI-4616 b constitutes a valuable benchmark system for comparative studies of terrestrial planets around mid-M dwarfs and for future atmospheric investigations.

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arXiv2026

TOI-1080 b: a temperate, rocky planet orbiting a quiet M4V host

We present the detection and validation of a small, temperate transiting exoplanet orbiting TOI-1080 every 3.9652482$^{+0.0000014}_{-0.0000015}$ days. The host is a quiet M4V star at 25.6 pc. The planet signal was first detected by TESS and validated using TESS and ground-based observations. By fitting the available light curves, the planet radius is measured to be 1.200+- 0.058 Rearth and its equilibrium temperature of 368$^{+12}_{-10}$ K. With NIRPS radial velocities, we are able to place a 3-sigma upper limit on the mass of TOI-1080 b of 10.7 Mearth. Our injection-recovery tests enable us to discard additional transiting planets in the TOI-1080 system with radii down to 0.9 Rearth and periods between 0.5 and 7.7 days, and planets with radii larger than 1.4 Rearth for periods up to 19 days. We demonstrate that it is highly amenable to characterisation of its mass and putative atmosphere. In particular, we find that TOI-1080 b is an exceptional target for the ongoing JWST+HST Rocky Worlds DDT programme, having a priority score that is higher than four out of nine targets currently being investigated by the programme. TOI-1080 b can be added to the sample of nearby benchmark planets accessible for detailed study with JWST.

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arXiv2026

The GAPS Programme at the TNG: LXX. TOI-5734b: A hot sub-Neptune orbiting a relatively young K dwarf with an Earth-like density

Increasing interest in young exoplanets is leading to a growing effort to understand the formation and evolutionary processes responsible for their different architectures. One interesting target is TOI-5734, a relatively young K3-K4 dwarf star ($500_{-150}^{+300}$ Myr) showing a transiting candidate in photometric observations followed up with high-resolution spectroscopic data. Using Transiting Exoplanet Survey Satellite (TESS) photometry and High Accuracy Radial velocity Planet Searcher for the Northern hemisphere (HARPS-N) radial-velocity (RV) data, we aim to validate the presence of the companion TOI-5734b, measure its planetary mass, size, and its orbital parameters after having characterised its host star. We then aim to study its possible planetary composition and atmospheric evolution. By simultaneously modelling photometry and high-cadence RVs, we measured the radius, mass, and density of TOI-5734b precisely. In particular, we employed Gaussian processes (GPs) with a flexible kernel to discriminate between the stellar activity of the young host and planetary signals. We confirmed the planetary nature of TOI-5734b and measured its orbital period ($P_{\rm b}\sim6.18$ d), radius ($R_{\rm b} = 2.10^{+0.12}_{-0.12}$ $R_\oplus$), and mass ($M_{\rm b}=9.1^{+2.6}_{-2.6}$ $M_\oplus$). By measuring its density ($\rho_{\rm b}=0.98_{-0.30}^{+0.36}$ $\rho_\oplus$), we infer that TOI-5734b is close to having a rocky composition and an almost completely depleted primary envelope. Our results point toward the possibility of considering the target for atmospheric studies with present and future ground- and space-based facilities.

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arXiv2026

Hidden Gems in TESS: sherlock finds two new rocky planets around nearby M dwarfs

The Hidden Gems project searches the TESS data for additional planets transiting low-mass stars in confirmed systems. Our goal is to identify planet candidates that are below the detection threshold set by the SPOC and QLP pipelines using sherlock, a specialized pipeline for robust detection and vetting of transit signals in TESS data. We present the discovery of two inner rocky planets in the TOI-237 and TOI-4336 A systems, confirmed with ground-based photometry from the TRAPPIST, SPECULOOS, ExTrA, and LCO facilities. TOI-237 c has a radius of 1.21 +/- 0.04Re, orbits its mid-M host star every 1.74 days, and is close to a 3:1 mean-motion resonance with TOI-237 b. TOI-4336 A c has a radius of 1.17 +/- 0.06Re, and orbits with a period of 7.58 days an M3.5 host star which is part of a hierarchical triple system. We performed model comparison to search for non-zero eccentricities, and found that the circular transit models are statistically favored. Dynamical simulations show that both systems are in stable configurations, and the TTVs expected for the TOI-237 system are of the order of seconds. TOI-237 c and TOI-4336 A c join the high-interest population of warm likely super-Earths below the so-called "radius valley". In particular, TOI-237 c is a good candidate for phase curve observations with JWST/MIRI thanks to the small radius of the host star and its short period.

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arXiv2026

Characterization of two new transiting sub-Neptunes and a terrestrial planet around M-dwarf hosts

We report the confirmation of three transiting exoplanets orbiting TOI-1243 (LSPM~J0902+7138), TOI-4529 (G~2--21), and TOI-5388 (Wolf~346) that were initially detected by TESS through ground-based photometry and radial velocity follow-up measurements with CARMENES. The planets present short orbital periods of $4.65$, $5.88$, and $2.59$ days, and they orbit early-M dwarfs (M2.0V, M1.5V, and M3.0V, respectively). We were able to precisely determine the radius of all three planets with a precision of $< 7\, \%$, the mass of TOI-1243 b with a precision of $19\, \%$, and upper mass limits for TOI-4529 b and TOI-5388 b. The radius of TOI-1243 b is $2.33\pm0.12\, {R_{\oplus}}$, its mass is $7.7 \pm 1.5\,{M_{\oplus}}$, and the mean density is $0.61 \pm 0.15 \, {\rho_\oplus}$. The radius of TOI-4529 b is $1.77 ^{+0.09}_{-0.08} \, {R_{\oplus}}$, the $3 {\sigma}$ upper mass limit is $4.9 \, {M_{\oplus}}$, and the $3 {\sigma}$ upper density limit is $0.88\, {\rho_\oplus}$. The third planet, TOI-5388 b, is Earth-sized with a radius of $0.99 ^{+0.07}_{-0.06} \, {R_{\oplus}}$, a $3 {\sigma}$ upper mass limit of $2.2 \, {M_{\oplus}}$, and a $3 {\sigma}$ upper density limit of $2.2\, {\rho_\oplus}$. While TOI-5388 b is most probably rocky, given its Earth-like radius, TOI-1243 b and TOI-4529 b are located in a highly degenerate region in the mass-radius space. TOI-4529 b appears to lean toward a water-world composition. TOI-1243 b has enough mass to host a significant H-He envelope, although a water-world and pure rocky compositions are also consistent with the data. Our analysis indicates that future atmospheric observations using JWST can aid in determining their real composition. The sample of small planets around M dwarfs is widely used to understand planet formation and composition theories, and our study adds three planets to this sample.

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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

The GAPS programme at TNG LXXI. A sub-Neptune suitable for atmospheric characterization in a multiplanet and mutually inclined system orbiting the bright K dwarf TOI-5789 (HIP 99452)

Sub-Neptunes with planetary radii of $R_{p} \simeq 2-4 R_{\oplus}$ are the most common planets around solar-type stars in short-period ($P<100$ d) orbits. It is still unclear, however, what their most likely composition is, that is whether they are predominantly gas dwarfs or water worlds. The sub-Neptunes orbiting bright host stars are very valuable because they are suitable for atmospheric characterization, which can break the well-known degeneracy in planet composition from the planet bulk density, when combined with a precise and accurate mass measurement. Here we report on the characterization of the sub-Neptune TOI-5789 c, which transits in front of the bright ($V=7.3$ mag and $K_{s}=5.35$ mag) and magnetically inactive K1V dwarf HIP 99452 every 12.93 days, thanks to TESS photometry and 141 high-precision radial velocities obtained with the HARPS-N spectrograph. We find that its radius, mass, and bulk density are $R_{c}=2.86^{+0.18}_{-0.15} R_\oplus$, $M_{c}=5.00 \pm 0.50 M_\oplus$, and $\rho_{c}=1.16 \pm 0.23$ g cm$^{-3}$, and we show that TOI-5789 c is a promising target for atmospheric characterization with both JWST and, in the future, Ariel. By analyzing the HARPS-N radial velocities with different tools, we also detected three additional non-transiting planets, namely TOI-5789 b, d, and e, with orbital periods and minimum masses of $P_{b}=2.76$ d, $M_{b}\sin{i}=2.12 \pm 0.28 M_\oplus$, $P_{d}=29.6$ d, $M_{d}\sin{i}=4.29 \pm 0.68 M_\oplus$, and $P_{e}=63.0$ d, $M_{e}\sin{i}=11.61 \pm 0.97 M_\oplus$. TOI-5789 is a mutually inclined system as the difference between the orbital inclinations of planets b and c must be higher than $\sim4$ deg. Nevertheless, from sensitivity studies based on both the HARPS-N and archival HIRES radial-velocity measurements, we can exclude that these relatively high mutual inclinations are due to the perturbation by an outer gaseous giant planet.

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arXiv2025

MANGOS II: Five new giant planets orbiting low-mass stars

Giant planets orbiting low-mass stars on short orbits present a conundrum, as in the most extreme cases their existence cannot be reconciled with current models of core accretion. Therefore, surveys dedicated to finding these rare planets have a key role to play by growing the sample to overcome small number statistics. In this work we present MANGOS, a programme dedicated to the search for giant objects (planets, brown dwarfs, and low-mass stars) orbiting M dwarfs. We report on the discovery of five new giant planets (TOI-3288 Ab, TOI-4666 b, TOI-5007 b, TOI-5292 Ab, TOI-5916 b) first detected by TESS, and confirmed using ground-based photometry and spectroscopy. The five planets have radii in the range 0.99-1.12 $\mathrm{R_{Jup}}$, masses between 0.49--1.69~$\mathrm{M_{Jup}}$, and orbital periods between 1.43 and 2.91 days. We reveal that TOI-3288 and TOI-5292 are wide binaries, and in the case of TOI-5292 we are able to characterise both stellar components. We demonstrate that the planets presented are suitable for further characterisation of their obliquities and atmospheres. We detect a small but significant eccentricity for TOI-5007 b, although for this to be more robust, more observations are needed to fully sample the orbit. Finally, we reveal a correlation between stellar metallicity and planet bulk density for giant planets orbiting low-mass stars.

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arXiv2025

A transiting hot Jupiter with two outer siblings orbiting an intermediate-mass post main-sequence star

Exoplanetary systems with multiple giant planets present an opportunity to understand planet formation, migration processes, and long-term system-wide dynamical interactions. In particular, they provide constraints to distinguish between smooth disk-driven migration or more dynamically excited system evolution pathways. We report the discovery and characterization of a unique multi-planet system hosting three gas giant planets orbiting the post-main sequence star TOI-375. The innermost planet, TOI-375 b, was initially detected by the TESS mission and then confirmed with photometric follow-up observations conducted using MEarth and LCOGT, and radial velocity measurements obtained with FEROS and CHIRON. The radial velocity data revealed the presence of two additional planetary candidates, TOI-375 c and TOI-375 d. We find that TOI-375 b is a hot Jupiter with an orbital period of $9.45469 \pm 0.00002$ days, mass $0.745 \pm 0.053,M_\mathrm{J}$, radius $0.961 \pm 0.043, R_\mathrm{J}$, and eccentricity $0.087 \pm 0.042$. The outer two planets, TOI-375 c and TOI-375 d, are warm-cold and cold Jupiters with orbital periods of $115.5^{+2.0}_{-1.6}$ days and $297.9^{+28.9}_{-18.6}$ days, and minimum masses of $2.11 \pm 0.22, M_\mathrm{J}$ and $1.40 \pm 0.28, M_\mathrm{J}$, respectively. In terms of formation and overall system architecture, the physical properties of TOI-375 b are consistent with the core accretion scenario, while the current configuration of the system could be explained by both disk-driven and high-eccentricity migration scenarios. The discovery of TOI-375 as the first known system hosting three or more fully evolved gas giants, with at least one transiting planet, makes it an excellent candidate for testing formation and migration theories.

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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

Sibling Sub-Neptunes Around Sibling M Dwarfs: TOI-521 and TOI-912

Sub-Neptunes are absent in the Solar System, yet they are commonly found in our Galaxy. They challenge the internal structure models and prompt investigation on their formation, evolution, and atmospheres. We report the characterisation of new sub-Neptunes orbiting two similar M dwarfs, TOI-521 (T_eff=3544 K), and TOI-912 (T_eff=3572 K). Both stars host a candidate identified by TESS and are part of the THIRSTEE follow-up program, which aims at understanding the sub-Neptune population through precise characterisation studies on a population level. We analysed light curves, ground-based photometry and ESPRESSO, HARPS and IRD RVs to infer precise orbital and physical parameters. The two stars host nearly identical planets in terms of mass and radius. TOI-521 b is a transiting sub-Neptune in a 1.5-d orbit with radius and mass of R=1.98+/-0.14 R_e and M=5.3+/-1.0 M_e respectively. Moreover, we identified an additional candidate at 20.3 d, with a minimum mass of Msini=10.7+/-2.4 M_e currently not detected to transit. Similarly, TOI-912 b is a 4.7-d sub-Neptune with R=1.93+/-0.13 R_e and M=5.1+/-0.5 M_e. Interestingly, TOI-912 b likely has an unusually high eccentricity (e=0.58+/-0.02), and it is probably undergoing strong tidal dissipation. If such eccentricity is confirmed, it would make it one of the most eccentric sub-Neptunes known to date. TOI-521 b and TOI-912 b have very similar densities (4 g/cm^3) and they lie in the degenerate region of the mass-radius diagram where different compositions are plausible, including a volatile-rich composition, or a rocky core surrounded by a H-He envelope. Our sample supports the division of sub-Neptunes into two distinct populations divided by a density gap. Both planets are interesting targets for atmospheric follow-up in the context of understanding the temperature-atmospheric feature trend that starts to emerge thanks to JWST observations.

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arXiv2025

Two warm Earth-sized exoplanets and an Earth-sized candidate in the M5V-M6V binary system TOI-2267

We report two warm Earth-sized exoplanets orbiting the close binary TOI-2267 (M5+M6, separation ~8 au). Data from TESS and ground-based facilities confirm the planets, but we cannot determine which star they orbit. The planets have radii of 1.00+/-0.11 R_Earth (TOI-2267 b, P=2.28 d) and 1.14+/-0.13 R_Earth (TOI-2267 c, P=3.49 d) if around TOI-2267A, or 1.22+/-0.29 R_Earth and 1.36+/-0.33 R_Earth if around TOI-2267B. TESS also shows a candidate signal (TOI-2267.02, P=2.03 d, 0.95+/-0.12 or 1.13+/-0.30 R_Earth). Dynamical analysis shows all three cannot orbit one star; the most stable configuration has planets b and c (near a 3:2 resonance) orbiting one star and the candidate the other. This scenario would make TOI-2267 the most compact binary system known to host planets, with both components harbouring transiting worlds, offering a unique benchmark for studying planet formation and evolution in compact binary.

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arXiv2025

TOI-1743 b, TOI-5799 b, TOI-5799 c and TOI-6223 b: TESS discovery and validation of four super-Earth to Neptune-sized planets around M dwarfs

We present the discovery by the TESS mission of one transiting Neptune-sized planet, TOI-6223 b and two transiting super-Earths, TOI-1743 b and TOI-5799 b. We validate these planets using a statistical validation method, multi-color light curves and other ancillary observations. We combined TESS and ground-based photometric data to constrain the physical properties of the planets. TOI-6223-b is slightly larger than Neptune ($R_p=5.12^{+0.24}_{-0.25}$ $R_\oplus$) orbiting an early M dwarf in 3.86 days, and it has an equilibrium temperature of $T_{\rm eq}=714\pm14$ K. TOI-1743 b orbits its M4V star every 4.27 days. It has a radius of $R_p=1.83^{+0.11}_{-0.10}$ $R_\oplus$ and an equilibrium temperature of $T_{\rm eq}=485^{+14}_{-13}$ K. TOI-5799 b has a radius of $R_p=1.733^{+0.096}_{-0.090}$ $R_\oplus$, and an equilibrium temperature of $T_{\rm eq}=505\pm16$ K orbits an M2 dwarf in 4.17 days. We also present the discovery of an additional transiting planet, TOI-5799 c, that we identified in the TESS data and validated using the SHERLOCK pipeline. TOI-5799 c is a super-Earth with a radius of $R_p=1.76^{+0.11}_{-0.10}$ $R_\oplus$. Its orbital period and its equilibrium temperature are 14.01 days and $T_{\rm eq}=337\pm11$ K, which place it near the inner edge of the habitable zone of its star.We show that these planets are suitable for both radial velocity follow-up and atmospheric characterization. They orbit bright (< 11 $K_{mag}$) early M dwarfs, making them accessible for precise mass measurements. The combination of the planet sizes and stellar brightness of their host stars also make them suitable targets for atmospheric exploration with the JWST. Such studies may provide insights into planet formation and evolution, as TOI-1743-b, TOI-5799-b, and TOI-5799-c lie within the so-called radius valley, while TOI-6223-b is located on the Neptunian ridge in the period-radius plane.

astro-ph.EP↗