arXiv subjects

M. Ghachoui

Publications and source records attributed to M. Ghachoui.

At least 19 recordsLinked to original sources

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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arXiv2025

ATREIDES I. Embarking on a trek across the exo-Neptunian landscape with the TOI-421 system

The distribution of close-in exoplanets is shaped by the interplay between atmospheric and dynamical processes. The Neptunian Desert, Ridge, and Savanna illustrate the sensitivity of these worlds to such processes, making them ideal to disentangle their roles. Determining how many Neptunes were brought close-in by early disk-driven migration (DDM; maintaining primordial spin-orbit alignment) or late high-eccentricity migration (HEM; generating large misalignments) is essential to understand how much atmosphere they lost. We propose a unified view of the Neptunian landscape to guide its exploration, speculating that the Ridge is a hot spot for evolutionary processes. Low-density Neptunes would mainly undergo DDM, getting fully eroded at shorter periods than the Ridge, while denser Neptunes would be brought to the Ridge and Desert by HEM. We embark on this exploration via ATREIDES, which relies on spectroscopy and photometry of 60 close-in Neptunes, their reduction with robust pipelines, and their interpretation through internal structure, atmospheric, and evolutionary models. We carried out a systematic RM census with VLT/ESPRESSO to measure the distribution of 3D spin-orbit angles, correlate its shape with system properties and thus relate the fraction of aligned-misaligned systems to DDM, HEM, and atmospheric erosion. Our first target, TOI-421c, lies in the Savanna with a neighboring sub-Neptune TOI-421b. We measured their 3D spin-orbit angles (Psib = 57+11-15 deg; Psic = 44.9+4.4-4.1 deg). Together with the eccentricity and possibly large mutual inclination of their orbits, this hints at a chaotic dynamical origin that could result from DDM followed by HEM. ATREIDES will provide the community with a wealth of constraints for formation and evolution models. We welcome collaborations that will contribute to pushing our understanding of the Neptunian landscape forward.

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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

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-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

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

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 $\rho_{\rm p}$ = $0.74 \pm 0.16$ $\rm g \, cm^{-3}$. 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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arXiv2024

TESS discovery of two super-Earths orbiting the M-dwarf stars TOI-6002 and TOI-5713 near the radius valley

We present the validation of two TESS super-Earth candidates transiting the mid-M dwarfs TOI-6002 and TOI-5713 every 10.90 and 10.44 days, respectively. The first star (TOI-6002) is located $32.038\pm0.019$ pc away, with a radius of $0.2409^{+0.0066}_{-0.0065}$ \rsun, a mass of $0.2105^{+0.0049}_{-0.0048}$ \msun, and an effective temperature of $3229^{+77}_{-57}$ K. The second star (TOI-5713) is located $40.946\pm0.032$ pc away, with a radius of $0.2985^{+0.0073}_{-0.0072}$ \rsun, a mass of $0.2653\pm0.0061$ \msun, and an effective temperature of $3225^{+41}_{-40}$ K. We validated the planets using TESS data, ground-based multi-wavelength photometry from many ground-based facilities, as well as high-resolution AO observations from Keck/NIRC2. TOI-6002 b has a radius of $1.65^{+0.22}_{-0.19}$ \re\ and receives $1.77^{+0.16}_{-0.11} S_\oplus$. TOI-5713 b has a radius of $1.77_{-0.11}^{+0.13} \re$ and receives $2.42\pm{0.11} S_\oplus$. Both planets are located near the radius valley and near the inner edge of the habitable zone of their host stars, which makes them intriguing targets for future studies to understand the formation and evolution of small planets around M-dwarf stars.

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arXiv2024

The Discovery and Follow-up of Four Transiting Short-period Sub-Neptunes Orbiting M dwarfs

Sub-Neptunes with $2-3R_\oplus$ are intermediate in size between rocky planets and Neptune-sized planets. The orbital properties and bulk compositions of transiting sub-Neptunes provide clues to the formation and evolution of close-in small planets. In this paper, we present the discovery and follow-up of four sub-Neptunes orbiting M dwarfs (TOI-782, TOI-1448, TOI-2120, and TOI-2406), three of which were newly validated by ground-based follow-up observations and statistical analyses. TOI-782 b, TOI-1448 b, TOI-2120 b, and TOI-2406 b have radii of $R_\mathrm{p} = 2.740^{+0.082}_{-0.079}\,R_\oplus$, $2.769^{+0.073}_{-0.068}\,R_\oplus$, $2.120\pm0.067\,R_\oplus$, and $2.830^{+0.068}_{-0.066}\,R_\oplus$ and orbital periods of $P = 8.02$, $8.11$, $5.80$, and $3.08$\,days, respectively. Doppler monitoring with Subaru/InfraRed Doppler instrument led to 2$σ$ upper limits on the masses of $<19.1\ M_\oplus$, $<19.5\ M_\oplus$, $<6.8\ M_\oplus$, and $<15.6\ M_\oplus$ for TOI-782 b, TOI-1448 b, TOI-2120 b, and TOI-2406 b, respectively. The mass-radius relationship of these four sub-Neptunes testifies to the existence of volatile material in their interiors. These four sub-Neptunes, which are located above the so-called ``radius valley'', are likely to retain a significant atmosphere and/or an icy mantle on the core, such as a water world. We find that at least three of the four sub-Neptunes (TOI-782 b, TOI-2120 b, and TOI-2406 b) orbiting M dwarfs older than 1 Gyr, are likely to have eccentricities of $e \sim 0.2-0.3$. The fact that tidal circularization of their orbits is not achieved over 1 Gyr suggests inefficient tidal dissipation in their interiors.

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arXiv2024

TOI-4336 A b: A temperate sub-Neptune ripe for atmospheric characterization in a nearby triple M-dwarf system

Small planets transiting bright nearby stars are essential to our understanding of the formation and evolution of exoplanetary systems. However, few constitute prime targets for atmospheric characterization, and even fewer are part of multiple star systems. This work aims to validate TOI-4336 A b, a sub-Neptune-sized exoplanet candidate identified by the TESS space-based transit survey around a nearby M-dwarf. We validate the planetary nature of TOI-4336 A b through the global analysis of TESS and follow-up multi-band high-precision photometric data from ground-based telescopes, medium- and high-resolution spectroscopy of the host star, high-resolution speckle imaging, and archival images. The newly discovered exoplanet TOI-4336 A b has a radius of 2.1$\pm$0.1R$_{\oplus}$. Its host star is an M3.5-dwarf star of mass 0.33$\pm$0.01M$_{\odot}$ and radius 0.33$\pm$0.02R$_{\odot}$ member of a hierarchical triple M-dwarf system 22 pc away from the Sun. The planet's orbital period of 16.3 days places it at the inner edge of the Habitable Zone of its host star, the brightest of the inner binary pair. The parameters of the system make TOI-4336 A b an extremely promising target for the detailed atmospheric characterization of a temperate sub-Neptune by transit transmission spectroscopy with JWST.

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arXiv2024

TOI-2266 b: a keystone super-Earth at the edge of the M dwarf radius valley

We validate the Transiting Exoplanet Survey Satellite (TESS) object of interest TOI-2266.01 (TIC 348911) as a small transiting planet (most likely a super-Earth) orbiting a faint M5 dwarf ($V=16.54$) on a 2.33~d orbit. The validation is based on an approach where multicolour transit light curves are used to robustly estimate the upper limit of the transiting object's radius. Our analysis uses SPOC-pipeline TESS light curves from Sectors 24, 25, 51, and 52, simultaneous multicolour transit photometry observed with MuSCAT2, MuSCAT3, and HiPERCAM, and additional transit photometry observed with the LCOGT telescopes. TOI-2266 b is found to be a planet with a radius of $1.54\pm\0.09\,R_\oplus$, which locates it at the edge of the transition zone between rocky planets, water-rich planets, and sub-Neptunes (the so-called M~dwarf radius valley). The planet is amenable to ground-based radial velocity mass measurement with red-sensitive spectrographs installed in large telescopes, such as MAROON-X and Keck Planet Finder (KPF), which makes it a valuable addition to a relatively small population of planets that can be used to probe the physics of the transition zone. Further, the planet's orbital period of 2.33 days places it inside a `keystone planet' wedge in the period-radius plane where competing planet formation scenarios make conflicting predictions on how the radius valley depends on the orbital period. This makes the planet also a welcome addition to the small population of planets that can be used to test small-planet formation scenarios around M~dwarfs.

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arXiv2023

A hot mini-Neptune and a temperate, highly eccentric sub-Saturn around the bright K-dwarf TOI-2134

We present the characterisation of an inner mini-Neptune in a 9.2292005$\pm$0.0000063 day orbit and an outer mono-transiting sub-Saturn planet in a 95.50$^{+0.36}_{-0.25}$ day orbit around the moderately active, bright (mv=8.9 mag) K5V star TOI-2134. Based on our analysis of five sectors of TESS data, we determine the radii of TOI-2134b and c to be 2.69$\pm$0.16 R$_{e}$ for the inner planet and 7.27$\pm$0.42 R$_{e}$ for the outer one. We acquired 111 radial-velocity spectra with HARPS-N and 108 radial-velocity spectra with SOPHIE. After careful periodogram analysis, we derive masses for both planets via Gaussian Process regression: 9.13$^{+0.78}_{-0.76}$ M$_{e}$ for TOI-2134b and 41.86$^{+7.69}_{-7.83}$ M$_{e}$ for TOI-2134c. We analysed the photometric and radial-velocity data first separately, then jointly. The inner planet is a mini-Neptune with density consistent with either a water-world or a rocky core planet with a low-mass H/He envelope. The outer planet has a bulk density similar to Saturn's. The outer planet is derived to have a significant eccentricity of 0.67$^{+0.05}_{-0.06}$ from a combination of photometry and RVs. We compute the irradiation of TOI-2134c as 1.45$\pm$0.10 times the bolometric flux received by Earth, positioning it for part of its orbit in the habitable sone of its system. We recommend further RV observations to fully constrain the orbit of TOI-2134c. With an expected Rossiter-McLaughlin (RM) effect amplitude of 7.2$\pm$1.3 m/s, we recommend TOI-2134c for follow-up RM analysis to study the spin-orbit architecture of the system. We calculate the Transmission Spectroscopy Metric, and both planets are suitable for bright-mode NIRCam atmospheric characterisation.

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arXiv2023

TESS discovery of a super-Earth orbiting the M dwarf star TOI-1680

We report the discovery by the TESS mission of a super-Earth on a 4.8-d orbit around an inactive M4.5 dwarf (TOI-1680) validated by ground-based facilities. The host star is located 37.14 pc away, with a radius of 0.2100+/-0.0064 R_sun, mass of 0.1800+/-0.0044 M_sun and an effective temperature of 3211+/-100 K. We validated and characterized the planet using TESS data, ground-based multi-wavelength photometry from TRAPPIST, SPECULOOS, and LCO, as well as high-resolution AO observations from Keck/NIRC2 and Shane. Our analyses have determined the following parameters for the planet: a radius of 1.466+0.063/-0.049 R_earth and an equilibrium temperature of 404+/-14 K, assuming no albedo and perfect heat redistribution. Assuming a mass based on mass-radius relations, this planet is a promising target for atmospheric characterization with the James Webb Space Telescope (JWST).

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arXiv2023

TOI-2084 b and TOI-4184 b: two new sub-Neptunes around M dwarf stars

We present the discovery and validation of two TESS exoplanets orbiting nearby M dwarfs: TOI-2084b, and TOI-4184b. We characterized the host stars by combining spectra from Shane/Kast and Magellan/FIRE, SED (Spectral Energy Distribution) analysis, and stellar evolutionary models. In addition, we used Gemini-South/Zorro & -North/Alopeke high-resolution imaging, archival science images, and statistical validation packages to support the planetary interpretation. We performed a global analysis of multi-colour photometric data from TESS and ground-based facilities in order to derive the stellar and planetary physical parameters for each system. We find that TOI-2084b and TOI-4184b are sub-Neptune-sized planets with radii of Rp = 2.47 +/- 0.13R_Earth and Rp = 2.43 +/- 0.21R_Earth, respectively. TOI-2084b completes an orbit around its host star every 6.08 days, has an equilibrium temperature of T_eq = 527 +/- 8K and an irradiation of S_p = 12.8 +/- 0.8 S_Earth. Its host star is a dwarf of spectral M2.0 +/- 0.5 at a distance of 114pc with an effective temperature of T_eff = 3550 +/- 50 K, and has a wide, co-moving M8 companion at a projected separation of 1400 au. TOI-4184b orbits around an M5.0 +/- 0.5 type dwarf star (Kmag = 11.87) each 4.9 days, and has an equilibrium temperature of T_eq = 412 +/- 8 K and an irradiation of S_p = 4.8 +/- 0.4 S_Earth. TOI-4184 is a metal poor star ([Fe/H] = -0.27 +/- 0.09 dex) at a distance of 69 pc with an effective temperature of T_eff = 3225 +/- 75 K. Both planets are located at the edge of the sub-Jovian desert in the radius-period plane. The combination of the small size and the large infrared brightness of their host stars make these new planets promising targets for future atmospheric exploration with JWST.

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arXiv2023

TOI-1442 b and TOI-2445 b: two potentially rocky ultra-short period planets around M dwarfs

Context. Exoplanets with orbital periods of less than one day are known as ultra-short period (USP) planets. They are relatively rare products of planetary formation and evolution processes, but especially favourable for characterisation with current planet detection methods. At the time of writing, 125 USP planets have already been confirmed. Aims. Our aim is to validate the planetary nature of two new transiting planet candidates around M dwarfs announced by the NASA Transiting Exoplanet Survey Satellite (TESS), registered as TESS Objects of Interest (TOIs) TOI-1442.01 and TOI-2445.01. Methods. We used TESS data, ground-based photometric light curves, and Subaru/IRD spectrograph radial velocity (RV) measurements to validate both planetary candidates and to establish their physical properties. Results. TOI-1442 b is a validated exoplanet with an orbital period of $P$=0.4090682+/-0.0000004 d, a radius of $R_p$=1.15+/-0.06$R_{\oplus}$, and equilibrium temperature of $T_{p,eq}$=1357$_{-42}^{+49}$K. TOI-2445 b is also validated with an orbital period of $P$=0.3711286+/-0.0000004 d, a radius of $R_p$= 1.33+/-0.09$R_{\oplus}$, and equilibrium temperature of $T_{p,eq}$=1330$_{-56}^{+61}$K. Their physical properties align with current empirical trends and formation theories of USP planets. Based on the RV measurements, we set 3$σ$ upper mass limits of 8$M_{\oplus}$ and 20$M_{\oplus}$, thus confirming the non-stellar, sub-Jovian nature of both transiting objects. More RV measurements will be needed to constrain the planetary masses and mean densities, and the predicted presence of outer planetary companions. These targets extend the small sample of USP planets orbiting around M dwarfs up to 21 members. They are also among the 20 most suitable terrestrial planets for atmospheric characterisation via secondary eclipse with the JWST, according to a widespread emission spectroscopy metric.

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arXiv2023

A super-Earth and a mini-Neptune near the 2:1 MMR straddling the radius valley around the nearby mid-M dwarf TOI-2096

Several planetary formation models have been proposed to explain the observed abundance and variety of compositions of super-Earths and mini-Neptunes. In this context, multitransiting systems orbiting low-mass stars whose planets are close to the radius valley are benchmark systems, which help to elucidate which formation model dominates. We report the discovery, validation, and initial characterization of one such system, TOI-2096, composed of a super-Earth and a mini-Neptune hosted by a mid-type M dwarf located 48 pc away. We first characterized the host star by combining different methods. Then, we derived the planetary properties by modeling the photometric data from TESS and ground-based facilities. We used archival data, high-resolution imaging, and statistical validation to support our planetary interpretation. We found that TOI-2096 corresponds to a dwarf star of spectral type M4. It harbors a super-Earth (R$\sim1.2 R_{\oplus}$) and a mini-Neptune (R$\sim1.90 R_{\oplus}$) in likely slightly eccentric orbits with orbital periods of 3.12 d and 6.39 d, respectively. These orbital periods are close to the first-order 2:1 mean-motion resonance (MMR), which may lead to measurable transit timing variations (TTVs). We computed the expected TTVs amplitude for each planet and found that they might be measurable with high-precision photometry delivering mid-transit times with accuracies of $\lesssim$2 min. Moreover, measuring the planetary masses via radial velocities (RVs) is also possible. Lastly, we found that these planets are among the best in their class to conduct atmospheric studies using the James Webb Space Telescope (JWST). The properties of this system make it a suitable candidate for further studies, particularly for mass determination using RVs and/or TTVs, decreasing the scarcity of systems that can be used to test planetary formation models around low-mass stars.

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arXiv2021

HATS-74Ab, HATS-75b, HATS-76b and HATS-77b: Four Transiting Giant Planets around K and M Dwarfs

The relative rarity of giant planets around low mass stars compared with solar-type stars is a key prediction from core accretion planet formation theory. In this paper we report on the discovery of four gas giant planets that transit low mass late K and early M dwarfs. The planets HATS-74Ab (TOI 737b), HATS-75b (TOI 552b), HATS-76b (TOI 555b), and HATS-77b (TOI 730b), were all discovered from the HATSouth photometric survey and followed-up using TESS and other photometric facilities. We use the new ESPRESSO facility at the VLT to confirm and systems and measure their masses. We find that that planets have masses of 1.46 +- 0.14 MJ , 0.491 +- 0.039 MJ , 2.629 +- 0.089 MJ and 1.374 +0.100-0.074 MJ , respectively, and radii of 1.032 +- 0.021 RJ , 0.884 +- 0.013 RJ , 1.079 +- 0.031 RJ , and 1.165 +- 0.021 RJ, respectively. The planets all orbit close to their host stars with orbital periods ranging from 1.7319 d to 3.0876 d. With further work we aim to test core accretion theory by using these and further discoveries to quantify the occurrence rate of giant planets around low mass host stars.

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arXiv2021

A large sub-Neptune transiting the thick-disk M4V TOI-2406

Large sub-Neptunes are uncommon around the coolest stars in the Galaxy and are rarer still around those that are metal-poor. However, owing to the large planet-to-star radius ratio, these planets are highly suitable for atmospheric study via transmission spectroscopy in the infrared, such as with JWST. Here we report the discovery and validation of a sub-Neptune orbiting the thick-disk, mid-M dwarf star TOI-2406. We first infer properties of the host star by analysing the star's near-infrared spectrum, spectral energy distribution, and Gaia parallax. We use multi-band photometry to confirm that the transit event is on-target and achromatic, and we statistically validate the TESS signal as a transiting exoplanet. We then determine physical properties of the planet through global transit modelling of the TESS and ground-based time-series data. We determine the host to be a metal-poor M4V star, located at a distance of 56 pc, with a sub-solar metallicity $(\mathrm{[Fe/H] = -0.38 \pm 0.07})$, and a member of the thick disk. The planet is a relatively large sub-Neptune for the M-dwarf planet population, with $\mathrm{R_p = 2.94 \pm 0.17} \mathrm{R_\oplus}$ and $\mathrm{P = 3.077}$ d, producing transits of 2% depth. We note the orbit has a non-zero eccentricity to 3$\mathrmσ$, prompting questions about the dynamical history of the system. This system is an interesting outcome of planet formation and presents a benchmark for large-planet formation around metal-poor, low-mass stars. The system warrants further study, in particular radial velocity follow-up to determine the planet mass and constrain possible bound companions. Furthermore, TOI-2406 b is a good target for future atmospheric study through transmission spectroscopy, particularly in the category of warm sub-Neptunes.

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