arXiv subjects

K. A. Collins

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

At least 37 records · Page 2Linked to original sources

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

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.

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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

The Hot Neptune Initiative (HONEI) II. TOI-5795 b: A hot super-Neptune orbiting a metal-poor star

The formation of Neptune planets with orbital periods less than 10\,days remains uncertain. They might have developed similarly to longer-period counterparts, emerged from rare collisions between smaller planets, or could be the remnant cores of stripped giant planets. Characterizing a large number of them is important to advance our understanding of how they form and evolve. We aimed at confirming the planetary nature and characterizing the properties of a close-in Neptune-type transiting exoplanet candidate revealed by TESS around the star TOI-5795 (V = 10.7 mag), 162 pc away from the Sun. We monitored TOI-5795 with the HARPS spectrograph for two months to quantify periodic variations in radial velocity (RV) to estimate the mass of the smaller companion. We combined these RV and TESS photometry. High-angular-resolution speckle and adaptive optics imaging excluded contamination from nearby sources. We found that the parent star is a metal-poor (${\rm [Fe/H]}=-0.27\pm0.07$), G3\,V star ($T_{\rm eff}=5718\pm50$\,K), with $R_{\star}=1.082\pm0.026\,R_{\sun}$, $M_{\star}=0.901^{+0.055}_{-0.037}\,M_{\sun}$ and $10.2^{+2.5}_{-3.3}$\,Gyr. We estimated that the planet has an orbital period of $P_{\rm orb}=6.1406325 \pm 0.0000054$ days and an orbital eccentricity compatible with zero. Having a mass of $23.66^{+4.09}_{-4.60}\,M_{\oplus}$, a radius of $5.62\pm 0.11\,R_{\oplus}$ and an equilibrium temperature of $1136\pm18$\,K, it can be considered as a hot super-Neptune at the edge of the Neptune desert. We simulated planet-formation processes but found almost no successful matches to the observed planet's mass and orbit, suggesting that post-formation dynamical events may have shaped its current state.

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arXiv2025

The Hot-Neptune Initiative (HONEI) I. Two hot sub-Neptunes on a close-in, eccentric orbit (TOI-5800 b) and a farther-out, circular orbit (TOI-5817 b)

Neptune-sized exoplanets are key targets for atmospheric studies, yet their formation and evolution remain poorly understood due to their diverse characteristics and limited sample size. The so-called "Neptune desert", a region of parameter space with a dearth of short-period sub- to super-Neptunes, is a critical testbed for theories of atmospheric escape and migration. The HONEI program aims to confirm and characterize the best Neptune-sized candidates for composition, atmospheric and population studies. By measuring planetary masses with high precision, we want to provide the community with optimal targets whose atmosphere can be effectively explored with the JWST or by ground-based high-resolution spectroscopy. For this purpose, we started a radial velocity follow-up campaign, using the twin high-precision spectrographs HARPS and HARPS-N, to measure the masses of TESS Neptune-sized candidates and confirm their planetary nature. In this first paper of the series, we confirm the planetary nature of two candidates: TOI-5800b and TOI-5817b. TOI-5800b is a hot sub-Neptune ($R_p=2.44\pm0.29$ $R_\oplus$, $M_p=9.4\pm1.8$ $M_\oplus$, $T_{eq} = 1108\pm20$ K) located at the lower edges of the Neptune desert ($P=2.628$ days) and is the most eccentric planet ($e\sim0.3$) ever found within $P<3$ d. TOI-5800b is expected to be still in the tidal migration phase with its parent star, a K3 V dwarf ($V=9.6$ mag), although its eccentricity could arise from interactions with another object in the system. Having a high-transmission spectroscopy metric ($TSM\sim103$), it represents a prime target for future atmospheric characterization. TOI-5817b is a relatively hot sub-Neptune ($R_p=3.08\pm0.14$ $R_\oplus$, $M_p=10.3\pm1.4$ $M_\oplus$, $T_{eq}=950\pm21$ K) located in the Neptune savanna ($P=15.610$ d) [...]

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arXiv2025

TOI-2407 b: a warm Neptune in the desert

We present the validation of TOI-2407 b, a warm Neptune-sized planet with a radius of 4.26 $\pm$ 0.26 R$_\oplus$, orbiting an early M-type star with a period of 2.7 days and an equilibrium temperature of 705 $\pm$ 12 K. The planet was identified by TESS photometry and validated in this work through multi-wavelength ground-based follow-up observations. We include an observation with the novel CMOS-based infrared instrument SPIRIT at the SPECULOOS Southern Observatory. The high-precision transit data enabled by CMOS detectors underscore their potential for improving the detection and characterisation of exoplanets orbiting M-dwarfs, particularly in the infrared, where these stars emit most of their radiation. TOI-2407 b lies within the boundaries of the period-radius Neptune desert, an apparent scarcity of Neptune-sized planets at short orbits. Further characterisation of TOI-2407 b, such as radial velocity measurements, will refine its position within planetary demographic trends. This system also provides a comparison case for the well-studied Neptune-sized planet Gliese 436 b, of similar radius, period and stellar type. Comparison studies could aid the understanding of the formation and evolution of Neptune-like planets around M-dwarfs.

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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

TOI-5005 b: A super-Neptune in the savanna near the ridge

The Neptunian desert and savanna have recently been found to be separated by a ridge, an overdensity of planets in the period range of $\simeq$3-5 days. These features are thought to be shaped by dynamical and atmospheric processes, but their roles are not yet well understood. Our aim was to confirm and characterize the super-Neptune TESS candidate TOI-5005.01, which orbits a moderately bright (V = 11.8) solar-type star (G2 V) with an orbital period of 6.3 days. We confirm TOI-5005 b to be a transiting super-Neptune with a radius of $R_{\rm p}$ = $6.25\pm 0.24$ $\rm R_{\rm \oplus}$ ($R_{\rm p}$ = $0.558\pm 0.021$ $\rm R_{\rm J}$) and a mass of $M_{\rm p}$ = $32.7\pm 5.9$ $\rm M_{\oplus}$ ($M_{\rm p}$ = $0.103\pm 0.018$ $\rm M_{\rm J}$), which corresponds to a mean density of $ρ_{\rm p}$ = $0.74 \pm 0.16$ $\rm g \, cm^{-3}$. Our internal structure modelling indicates that the overall metal mass fraction is well constrained to a value slightly lower than that of Neptune and Uranus ($Z_{\rm planet}$ = $0.76^{+0.04}_{-0.11}$). We also estimated the present-day atmospheric mass-loss rate of TOI-5005 b, but found contrasting predictions depending on the choice of photoevaporation model. At a population level, we find statistical evidence ($p$-value = $0.0092^{+0.0184}_{-0.0066}$) that planets in the savanna such as TOI-5005 b tend to show lower densities than planets in the ridge, with a dividing line around 1 $\rm g \, cm^{-3}$, which supports the hypothesis of different evolutionary pathways populating the two regimes. TOI-5005 b is located in a key region of the period-radius space to study the transition between the Neptunian ridge and the savanna. It orbits the brightest star of all such planets, which makes it a target of interest for atmospheric and orbital architecture observations that will bring a clearer picture of its overall evolution.

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arXiv2025

TOI-3493 b: A planet with a Neptune-like density transiting a bright G0-type star

We report the discovery of TOI-3493 b, a sub-Neptune-sized planet on an 8.15-d orbit transiting the bright (V=9.3) G0 star HD 119355 (aka TIC 203377303) initially identified by NASA's TESS space mission. With the aim of confirming the planetary nature of the transit signal detected by TESS and determining the mass of the planet, we performed an intensive Doppler campaign with the HARPS spectrograph, collecting radial velocity measurements. We found that TOI-3493 b lies in a nearly circular orbit and has a mass of 9.0+/-1.2 M_earth and a radius of 3.22+/-0.08 R_earth, implying a bulk density of 1.47+/-0.23 g/cm^3, consistent with a composition comprising a small solid core surrounded by a thick H/He dominated atmosphere.

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arXiv2025

TESS and HARPS-N unveil two planets transiting TOI-1453. A super-Earth and one of the lowest mass sub-Neptunes

We report on the validation and characterisation of two transiting planets around TOI-1453, a K-dwarf star in the TESS northern continuous viewing zone. In addition to the TESS data, we used ground-based photometric, spectroscopic, and high-resolution imaging follow-up observations to validate the two planets. We obtained 100 HARPS-N high-resolution spectra over two seasons and used them together with the TESS light curve to constrain the mass, radius, and orbit of each planet. TOI-1453 b is a super-Earth with an orbital period of $P_b$=4.314 days, a radius of $R_b$=1.17$\pm$0.06$R_{\oplus}$, and a mass lower than 2.32$M_{\oplus}$ (99$\%$). TOI-1453 c is a sub-Neptune with a period of $P_c$=6.589 days, radius of $R_c$=2.22$\pm$0.09$R_{\oplus}$, and mass of $M_c$=2.95$\pm$0.84$M_{\oplus}$. The two planets orbit TOI-1453 with a period ratio close to 3/2, although they are not in a mean motion resonance (MMR) state. We did not detect any transit timing variations in our attempt to further constrain the planet masses. TOI-1453 c has a very low bulk density and is one of the least massive sub-Neptunes discovered to date. It is compatible with having either a water-rich composition or a rocky core surrounded by a thick H/He atmosphere. However, we set constraints on the water mass fraction in the envelope according to either a water-rich or water-poor formation scenario. The star TOI-1453 belongs to the Galactic thin disc based on Gaia kinematics and has a sub-solar metallicity. This system is orbited by a fainter stellar companion at a projected distance of about 150 AU, classifying TOI-1453 b and c of S-type planets. These various planetary and stellar characteristics make TOI-1453 a valuable system for understanding the origin of super-Earths and sub-Neptunes.

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arXiv2025

TOI-6508b: A massive transiting brown dwarf orbiting a low-mass star

We report the discovery of a transiting brown dwarf orbiting a low-mass star, TOI-6508b. Today, only ~50 transiting brown dwarfs have been discovered. TOI-6508b was first detected with data from the Transiting Exoplanet Survey Satellite (TESS) in Sectors 10, 37, and 63. Ground-based follow-up photometric data were collected with the SPECULOOS-South and LCOGT-1.0m telescopes, and RV measurements were obtained with the Near InfraRed Planet Searcher (NIRPS) spectrograph. We find that TOI-6508b has a mass of Mp=72.5+7.6-5.1MJup and a radius of Rp=1.03+/-0.03RJup. Our modeling shows that the data are consistent with an eccentric orbit of 19day and an eccentricity of e=0.28+0.09-0.08. TOI-6508b has a mass ratio of M_BD/Ms=0.40, makes it the second highest mass ratio brown dwarf that transits a low-mass star. The host has a mass of Ms=0.174+/-0.004M_Sun, a radius of Rs=0.205+/-0.006R_Sun, an effective temperature of Teff=2930+/-70K, and a metallicity of [Fe/H]=-0.22+/-0.08. This makes TOI-6508b an interesting discovery that has come to light in a region still sparsely populated.

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arXiv2025

TOI-2015b: a sub-Neptune in strong gravitational interaction with an outer non-transiting planet

TOI-2015 is a known exoplanetary system around an M4 dwarf star, consisting of a transiting sub-Neptune planet in a 3.35-day orbital period, TOI-2015b, accompanied by a non-transiting companion, TOI-2015c. High-precision RV measurements were taken with the MAROON-X spectrograph, and high-precision photometric data were collected several networks. We re-characterize the target star by combining optical spectr, Bayesian Model Averaging (BMA) and Spectral Energy Distribution (SED) analysis. The TOI-2015 host star is a K=10.3mag M4-type dwarf with a sub-solar metallicity of [Fe/H]=-0.31+/-0.16, and a Teff=3200K. Our photodynamical analysis of the system strongly favors the 5:3 mean motion resonance and in this scenario the planet b has an orbital period of 3.34days, a mass of Mp=9.02+/-0.34Me, a radius of Rp=3.309+/-0.012Re, resulting in a density of rhop= 1.40+/-0.06g/cm3, indicative of a Neptune like composition. Its transits exhibit large (>1hr) timing variations indicative of an outer perturber in the system. We performed a global analysis of the high-resolution RV measurements, the photometric data, and the TTVs, and inferred that TOI-2015 hosts a second planet, TOI-2015c, in a non-transiting configuration. TOI-2015c has an orbital period of Pc=5.583days and a mass of Mp=8.91+0.38-0.40Me. The dynamical configuration of TOI-2015b and TOI-2015c can be used to constrain the system's planetary formation and migration history. Based on the mass-radius composition models, TOI-2015b is a water-rich or rocky planet with a hydrogen-helium envelope. Moreover, TOI-2015b has a high transmission spectroscopic metric (TSM=149), making it a favorable target for future transmission spectroscopic observations with JWST to constrain the atmospheric composition of the planet. Such observations would also help to break the degeneracies in theoretical models of the planet's interior structure.

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arXiv2024

Characterisation of TOI-406 as showcase of the THIRSTEE program: A 2-planet system straddling the M-dwarf density gap

The exoplanet sub-Neptune population currently poses a conundrum, as to whether small-size planets are volatile-rich cores without an atmosphere, or rocky cores surrounded by a H-He envelope. To test the different hypotheses from an observational point of view, a large sample of small-size planets with precise mass and radius measurements is the first step. On top of that, much more information will likely be needed, including atmospheric characterisation and a demographic perspective on their bulk properties. We present here the concept and strategy of the THIRSTEE project, which aims to shed light on the composition of the sub-Neptune population across stellar types by increasing their number and improving the accuracy of bulk density measurements, as well as investigating their atmospheres and performing statistical, demographic analysis. We report the first results of the program, characterising a new two-planet system around the M-dwarf TOI-406. We analyse TESS and ground-based photometry, together with ESPRESSO and NIRPS/HARPS RVs to derive the orbital parameters and investigate the internal composition of the 2 planets orbiting TOI-406, which have radii and masses of $R_c = 1.32 \pm 0.12 R_{\oplus}$, $M_c = 2.08_{-0.22}^{+0.23} M_{\oplus}$ and $R_b = 2.08_{-0.15}^{+0.16} R_{\oplus}$, $M_b = 6.57_{-0.90}^{+1.00} M_{\oplus}$, and periods of $3.3$ and $13.2$ days, respectively. Planet c is consistent with an Earth-like composition, while planet b is compatible with multiple internal composition models, including volatile-rich planets without H/He atmospheres. The 2 planets are located in 2 distinct regions in the mass-density diagram, supporting the existence of a density gap among small exoplanets around M dwarfs. With an T$_{\rm eq}$ of only 368 K, TOI-406 b stands up as a particularly interesting target for atmospheric characterisation with JWST in the low-temperature regime.

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arXiv2024

Characterization of seven transiting systems including four warm Jupiters from SOPHIE and TESS

We present the study of seven systems, three of which TOI-2295, TOI-2537, and TOI-5110 are newly discovered planetary systems. Through the analysis of TESS photometry, SOPHIE radial velocities, and high-spatial resolution imaging, we found that TOI-2295b, TOI-2537b, and TOI-5110b are transiting warm Jupiters with orbital periods ranging from 30 to 94 d, masses between 0.9 and 2.9 MJ, and radii ranging from 1.0 to 1.5 RJ. Both TOI-2295 and TOI-2537 each harbor at least one additional, outer planet. Their outer planets TOI-2295c and TOI-2537c are characterized by orbital periods of 966.5 +/- 4.3 and 1920^{+230}_{-140} d, respectively, and minimum masses of 5.61^{+0.23}_{-0.24} and 7.2 +/- 0.5 MJ, respectively. We also investigated and characterized the two recently reported warm Jupiters TOI-1836b and TOI-5076b, which we independently detected in SOPHIE RVs. Additionally, we study the planetary candidates TOI-4081.01 and TOI-4168.01. For TOI-4081.01, despite our detection in radial velocities, we cannot rule out perturbation by a blended eclipsing binary and thus exercise caution regarding its planetary nature. On the other hand, we identify TOI-4168.01 as a firm false positive. Finally, we highlight interesting characteristics of these new planetary systems. The transits of TOI-2295b are highly grazing, with an impact parameter of 1.056$^{+0.063}_{-0.043}$. TOI-2537b, in turn, is a temperate Jupiter with an effective temperature of 307+/-15 K and can serve as a valuable low-irradiation control for models of hot Jupiter inflation anomalies. We also detected significant transit timing variations (TTVs) for TOI-2537b, which are likely caused by gravitational interactions with the outer planet TOI-2537c. Finally, TOI-5110b stands out due to its orbital eccentricity of 0.75+/- 0.03, one of the highest planetary eccentricities discovered thus far.

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arXiv2024

A joint effort to discover and characterize two resonant mini Neptunes around TOI-1803 with TESS, HARPS-N and CHEOPS

We present the discovery of two mini Neptunes near a 2:1 orbital resonance configuration orbiting the K0 star TOI-1803. We describe their orbital architecture in detail and suggest some possible formation and evolution scenarios. Using CHEOPS, TESS, and HARPS-N datasets we can estimate the radius and the mass of both planets. We used a multidimensional Gaussian Process with a quasi-periodic kernel to disentangle the planetary components from the stellar activity in the HARPS-N dataset. We performed dynamical modeling to explain the orbital configuration and performed planetary formation and evolution simulations. For the least dense planet, we define possible atmospheric characterization scenarios with simulated JWST observations. TOI-1803 b and TOI-1803 c have orbital periods of $\sim$6.3 and $\sim$12.9 days, respectively, residing in close proximity to a 2:1 orbital resonance. Ground-based photometric follow-up observations revealed significant transit timing variations (TTV) with an amplitude of $\sim$10 min and $\sim$40 min, respectively, for planet -b and -c. With the masses computed from the radial velocities data set, we obtained a density of (0.39$\pm$0.10) $ρ_{earth}$ and (0.076$\pm$0.038) $ρ_{earth}$ for planet -b and -c, respectively. TOI-1803 c is among the least dense mini Neptunes currently known, and due to its inflated atmosphere, it is a suitable target for transmission spectroscopy with JWST. We report the discovery of two mini Neptunes close to a 2:1 orbital resonance. The detection of significant TTVs from ground-based photometry opens scenarios for a more precise mass determination. TOI-1803 c is one of the least dense mini Neptune known so far, and it is of great interest among the scientific community since it could constrain our formation scenarios.

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arXiv2024

The GAPS Programme at TNG. LXV. Precise density measurement of TOI-1430 b, a young planet with an evaporating atmosphere

Small-sized exoplanets in tight orbits around young stars (10-1000 Myr) give us the opportunity to investigate the mechanisms that led to their formation, the evolution of their physical and orbital properties and, especially, of their atmospheres. Thanks to the all-sky survey carried out by TESS, many of these exoplanets have been discovered and have subsequently been characterized with dedicated follow-up observations. In the context of a collaboration among the GAPS, TKS and CPS teams, we measured with a high level of precision the mass and the radius of TOI-1430 b, a young (~700 Myr) exoplanet with an escaping He atmosphere orbiting the K-dwarf star HD 235088 (TOI-1430). By adopting appropriate stellar parameters, which were measured in this work, we were able to simultaneously model the signals due to strong stellar activity and the transiting planet TOI-1430 b in both photometric and spectroscopic series. This allowed us to measure the density of the planet with high precision, and reconstruct the evolution of its atmosphere. TOI-1430 is an active K-dwarf star born 700+/-150 Myr ago and rotates in ~12 d. It hosts a mini-Neptune whose orbital period is Pb=7.434133+/-0.000004 d. Thanks to long-term monitoring of this target performed with TESS, HARPS-N, HIRES, and APF, we estimated a radius Rb=1.98+/-0.07 $R_{\oplus}$, a mass Mb=4.2+/-0.8 $M_{\oplus}$, and thus a planetary density $ρ$b=0.5+/-0.1 $ρ_{\oplus}$. TOI-1430 b is hence a low-density mini-Neptune with an extended atmosphere, at the edge of the radius gap. Because this planet is known to have an evaporating atmosphere of He, we reconstructed its atmospheric history. Our analysis supports the scenario in which, shortly after its birth, TOI-1430 b may have been super-puffy, with a radius 5x-13x and a mass 1.5x-2x that of today; in ~200 Myr from now, TOI-1430 b should lose its envelope, showing its Earth-size core.

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arXiv2024

The GAPS programme at TNG LXIV: An inner eccentric sub-Neptune and an outer sub-Neptune-mass candidate around BD+00 444 (TOI-2443)

We examined in depth the star BD+00 444 (GJ 105.5, TOI-2443; V = 9.5 mag; d = 23.9 pc), with the aim of characterizing and confirming the planetary nature of its small companion, the planet candidate TOI-2443.01, which was discovered by TESS. We monitored BD+00 444 with the HARPS-N spectrograph for 1.5 years to search for planet-induced radial-velocity (RV) variations, and then analyzed the RV measurements jointly with TESS and ground-based photometry. We determined that the host is a quiet K5 V, and we revealed that the sub-Neptune BD+00 444 b has a radius of $R_b=2.36\pm0.05 R_{\oplus}$, a mass of $M_b=4.8\pm1.1 M_{\oplus}$ and, consequently, a rather low-density value of $ρ_b=2.00+0.49-0.45$ g cm-3, which makes it compatible with both an Earth-like rocky interior with a thin H-He atmosphere and a half-rocky, half-water composition with a small amount of H-He. Having an orbital period of about 15.67 days and an equilibrium temperature of about 519 K, BD+00 444 b has an estimated transmission spectroscopy metric of about 159, which makes it ideal for atmospheric follow-up with the JWST. Notably, it is the second most eccentric inner transiting planet, $e=0.302+0.051-0.035$, with a mass below 20 $M_{\oplus}$, among those with well-determined eccentricities. We estimated that tidal forces from the host star affect both planet b's rotation and eccentricity, and strong tidal dissipation may signal intense volcanic activity. Furthermore, our analysis suggests the presence of a sub-Neptune-mass planet candidate, BD+00 444 c, having an orbital period of $P=96.6\pm1.4$ days, and a minimum mass $M\sin{i}=9.3+1.8-2.0 M_{\oplus}$. With an equilibrium temperature of about 283 K, BD+00 444 c is right inside the habitable zone; however, this candidate necessitates further observations and stronger statistical evidence to be confirmed. [...]

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