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Context. The Neptunian desert and savanna have recently been found to be separated by a ridge, an overdensity of planets in the period range of ≃3–5 days. These features are thought to be shaped by dynamical and atmospheric processes. However, their roles are not yet well understood. Aims. 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. With these properties, TOI-5005.01 is located in the Neptunian savanna near the ridge. Methods. We used Bayesian inference to analyse 38 HARPS radial velocity measurements, three sectors of TESS photometry, and two PEST and TRAPPIST-South transits. We tested a set of models involving eccentric and circular orbits, long-term drifts, and Gaussian processes to account for correlated stellar and instrumental noise. We computed the Bayesian evidence to find the model that best represents our dataset and infer the orbital and physical properties of the system. Results. We confirm TOI-5005 b to be a transiting super-Neptune with a radius of Rp = 6.25 ± 0.24 R⊕ (Rp = 0.558 ± 0.021 RJ) and a mass of Mp = 32.7 ± 5.9 M⊕ (Mp = 0.103 ± 0.018 MJ), which corresponds to a mean density of ρp = 0.74 ± 0.16 g cm−3. Our internal structure modelling indicates that the core mass fraction (CMF = 0.74−0.45+0.05) and envelope metal mass fraction (Zenv = 0.08−0.06+0.41) of TOI-5005 b are degenerate, but the overall metal mass fraction is well constrained to a value slightly lower than that of Neptune and Uranus (Zplanet = 0.76−0.11+0.04). The Zplanet /Zstar ratio is consistent with the well-known mass-metallicity relation, which suggests that TOI-5005 b was formed via core accretion. 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 (0.013 ± 0.008 M⊕ Gyr−1 vs. 0.17 ± 0.12 M⊕ Gyr−1). At a population level, we find statistical evidence (p-value = 0.0092−0.0066+0.0184) 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 g cm−3 , which supports the hypothesis of different evolutionary pathways populating the two regimes. Conclusions. TOI-5005 b is located in a region of the period-radius space that is key to studying the transition between the Neptunian ridge and the savanna. It orbits the brightest star of all such planets known today, which makes it a target of interest for atmospheric and orbital architecture observations that will bring a clearer picture of its overall evolution. [ABSTRACT FROM AUTHOR]

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 ± 0.019 pc away, with a radius of 0.2409−0.0065+0.0066 R⊙, a mass of 0.2105−0.0048+0.0049 M⊙, and an effective temperature of 3229−57+77 K. The second star (TOI-5713) is located 40.946 ± 0.032 pc away, with a radius of 0.2985−0.0072+0.0073 R⊙, a mass of 0.2653 ± 0.0061 M⊙, and an effective temperature of 3225−40+41 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 1.65−0.19+0.22 R⊕ and receives 1.77−0.110.16S⊕. TOI-5713 b has a radius of 1.77−0.11+0.13 R⊕ and receives 2.42 ± 0.11S⊕. 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. [ABSTRACT FROM AUTHOR]

The TESS mission searches for transiting exoplanets by monitoring the brightness of hundreds of thousands of stars across the entire sky. M-type planet hosts are ideal targets for this mission due to their smaller size and cooler temperatures, which makes it easier to detect smaller planets near or within their habitable zones. Additionally, M dwarfs have a smaller contrast ratio between the planet and the star, making it easier to measure the planet's properties accurately. Here, we report the validation analysis of 13 TESS exoplanet candidates orbiting around M dwarfs. We studied the nature of these candidates through a multi-colour transit photometry transit analysis using several ground-based instruments (MuSCAT2, MuSCAT3, and LCO-SINISTRO), high-spatial resolution observations, and TESS light curves. We present the validation of five new planetary systems: TOI-1883b, TOI-2274b, TOI-2768b, TOI-4438b, and TOI-5319b, along with compelling evidence of a planetary nature for TOIs 2781b and 5486b. We also present an empirical definition for the Neptune desert boundaries. The remaining six systems could not be validated due to large true radius values overlapping with the brown dwarf regime or, alternatively, the presence of chromaticity in the MuSCAT2 light curves. [ABSTRACT FROM AUTHOR]

Context. 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. Aims. 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. Methods. We validated 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. Results. The newly discovered exoplanet TOI-4336 A b has a radius of 2.1 ± 0.1 R⊕. Its host star is an M3.5-dwarf star with a mass of 0.33 ± 0.01 M⊙ and a radius of 0.33 ± 0.02 R⊙, and is a 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, which is 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. [ABSTRACT FROM AUTHOR]

We report the discovery by the TESS mission of a super-Earth on a 4.8-days 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⊙, mass of 0.1800 ± 0.0044 M⊙, 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 1.466−0.049+0.063R⊕ 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). [ABSTRACT FROM AUTHOR]