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Abstract We present the confirmation of TOI-5573 b, a Saturn-sized exoplanet on an 8.79 days orbit around an early M dwarf (3790 K, 0.59R_⊙, 0.61M_⊙, 12.30 Jmag). TOI-5573 b has a mass of $112_{-19}^{+18}$M_⊕(0.35 ± 0.06M_Jup) and a radius of 9.75 ± 0.47R_⊕(0.87 ± 0.04R_Jup), resulting in a density of $0.66_{-0.13}^{+0.16}$g cm⁻³, akin to that of Saturn. The planet was initially discovered by the Transiting Exoplanet Survey Satellite (TESS) and confirmed using a combination of 11 transits from four TESS Sectors (20, 21, 47, and 74), ground-based photometry from the Red Buttes Observatory, and high-precision radial velocity data from the Habitable-zone Planet Finder and NN-EXPLORE Exoplanet Investigations with Doppler spectrographs, achieving a 5σprecision on the planet’s mass. TOI-5573 b is one of the coolest Saturn-like exoplanets discovered around an M-dwarf, with an equilibrium temperature of only 528 ± 10 K, making it a valuable target for atmospheric characterization. Saturn-like exoplanets around M dwarfs likely form through core accretion, with increased disk opacity slowing gas accretion and limiting their mass. The host star’s supersolar metallicity supports core accretion, but uncertainties in M-dwarf metallicity estimates complicate definitive conclusions. Compared to other GEMS (Giant Exoplanets around M-dwarf Stars) orbiting metal-rich stars, TOI-5573 b aligns with the observed pattern that giant planets preferentially form around M-dwarfs with supersolar metallicity. Further high-resolution spectroscopic observations are needed to explore the role of stellar metallicity in shaping the formation and properties of giant exoplanets like TOI-5573 b. 

Abstract Gaia astrometry of nearby stars is precise enough to detect the tiny displacements induced by substellar companions, but radial velocity (RV) data are needed for definitive confirmation. Here we present RV follow-up observations of 28 M and K stars with candidate astrometric substellar companions, which led to the confirmation of two systems, Gaia-4b and Gaia-5b, identification of five systems that are single lined but require additional data to confirm as substellar companions, and the refutation of 21 systems as stellar binaries. Gaia-4b is a massive planet (M = 11.8 ± 0.7M_J) in aP = 571.3 ± 1.4 day orbit with a projected semimajor axisa₀ = 0.312 ± 0.040 mas orbiting a 0.644 ± 0.02M_⊙star. Gaia-5b is a brown dwarf (M = 20.9 ± 0.5M_J) in aP = 358.62 ± 0.20 days eccentrice = 0.6423 ± 0.0026 orbit with a projected angular semimajor axis ofa₀ = 0.947 ± 0.038 mas around a 0.34 ± 0.03M_⊙star. Gaia-4b is one of the first exoplanets discovered via the astrometric technique, and is one of the most massive planets known to orbit a low-mass star. 

Abstract We confirm TOI-4201 b as a transiting Jovian-mass planet orbiting an early M dwarf discovered by the Transiting Exoplanet Survey Satellite. Using ground-based photometry and precise radial velocities from NEID and the Planet Finder Spectrograph, we measure a planet mass of ${2.59}_{-0.06}^{+0.07}$M_J, making this one of the most massive planets transiting an M dwarf. The planet is ∼0.4% of the mass of its 0.63M_⊙host and may have a heavy-element mass comparable to the total dust mass contained in a typical class II disk. TOI-4201 b stretches our understanding of core accretion during the protoplanetary phase and the disk mass budget, necessitating giant planet formation to take place either much earlier in the disk lifetime or perhaps through alternative mechanisms like gravitational instability. 

We report the discovery of TOI-4641b, a warm Jupiter transiting a rapidly rotating F-type star with a stellar effective temperature of 6560 K. The planet has a radius of 0.73 RJup, a mass smaller than 3.87 MJup(3σ), and a period of 22.09 d. It is orbiting a bright star (V=7.5 mag) on a circular orbit with a radius and mass of 1.73 R⊙ and 1.41 M⊙. Follow-up ground-based photometry was obtained using the Tierras Observatory. Two transits were also observed with the Tillinghast Reflector Echelle Spectrograph, revealing the star to have a low projected spin-orbit angle (λ=$$1.41^{+0.76}_{-0.76}$$°). Such obliquity measurements for stars with warm Jupiters are relatively few, and may shed light on the formation of warm Jupiters. Among the known planets orbiting hot and rapidly rotating stars, TOI-4641b is one of the longest period planets to be thoroughly characterized. Unlike hot Jupiters around hot stars which are more often misaligned, the warm Jupiter TOI-4641b is found in a well-aligned orbit. Future exploration of this parameter space can add one more dimension to the star–planet orbital obliquity distribution that has been well sampled for hot Jupiters. 

Abstract Giant exoplanets orbiting close to their host stars are unlikely to have formed in their present configurations¹. These ‘hot Jupiter’ planets are instead thought to have migrated inward from beyond the ice line and several viable migration channels have been proposed, including eccentricity excitation through angular-momentum exchange with a third body followed by tidally driven orbital circularization^2,3. The discovery of the extremely eccentric (e = 0.93) giant exoplanet HD 80606 b (ref. ⁴) provided observational evidence that hot Jupiters may have formed through this high-eccentricity tidal-migration pathway⁵. However, no similar hot-Jupiter progenitors have been found and simulations predict that one factor affecting the efficacy of this mechanism is exoplanet mass, as low-mass planets are more likely to be tidally disrupted during periastron passage^6–8. Here we present spectroscopic and photometric observations of TIC 241249530 b, a high-mass, transiting warm Jupiter with an extreme orbital eccentricity ofe = 0.94. The orbit of TIC 241249530 b is consistent with a history of eccentricity oscillations and a future tidal circularization trajectory. Our analysis of the mass and eccentricity distributions of the transiting-warm-Jupiter population further reveals a correlation between high mass and high eccentricity. 

Abstract We present the discovery of a new Jovian-sized planet, TOI-3757 b, the lowest-density transiting planet known to orbit an M dwarf (M0V). This planet was discovered around a solar-metallicity M dwarf, using Transiting Exoplanet Survey Satellite photometry and confirmed with precise radial velocities from the Habitable-zone Planet Finder (HPF) and NEID. With a planetary radius of 12.0 − 0.5 + 0.4 R ⊕ and mass of 85.3 − 8.7 + 8.8 M ⊕ , not only does this object add to the small sample of gas giants (∼10) around M dwarfs, but also its low density ( ρ = 0.27 − 0.04 + 0.05 g cm −3 ) provides an opportunity to test theories of planet formation. We present two hypotheses to explain its low density; first, we posit that the low metallicity of its stellar host (∼0.3 dex lower than the median metallicity of M dwarfs hosting gas giants) could have played a role in the delayed formation of a solid core massive enough to initiate runaway accretion. Second, using the eccentricity estimate of 0.14 ± 0.06, we determine it is also plausible for tidal heating to at least partially be responsible for inflating the radius of TOI-3757b b. The low density and large scale height of TOI-3757 b makes it an excellent target for transmission spectroscopy studies of atmospheric escape and composition (transmission spectroscopy measurement of ∼ 190). We use HPF to perform transmission spectroscopy of TOI-3757 b using the helium 10830 Å line. Doing this, we place an upper limit of 6.9% (with 90% confidence) on the maximum depth of the absorption from the metastable transition of He at ∼10830 Å, which can help constraint the atmospheric mass-loss rate in this energy-limited regime. 

Abstract The warm Neptune GJ 3470b transits a nearby (d= 29 pc) bright slowly rotating M1.5-dwarf star. Using spectroscopic observations during two transits with the newly commissioned NEID spectrometer on the WIYN 3.5 m Telescope at Kitt Peak Observatory, we model the classical Rossiter–McLaughlin effect, yielding a sky-projected obliquity of $\lambda ={98}_{-12}^{+15◦}$and a $v\sin i={0.85}_{-0.33}^{+0.27}\mathrm{km}{\mathrm{s}}^{-1}$. Leveraging information about the rotation period and size of the host star, our analysis yields a true obliquity of $\psi ={95}_{-8}^{+9◦}$, revealing that GJ 3470b is on a polar orbit. Using radial velocities from HIRES, HARPS, and the Habitable-zone Planet Finder, we show that the data are compatible with a long-term radial velocity (RV) slope of $\dot{\gamma }=-0.0022\pm 0.0011\mathrm{m}{\mathrm{s}}^{-1}{\mathrm{day}}^{-1}$over a baseline of 12.9 yr. If the RV slope is due to acceleration from another companion in the system, we show that such a companion is capable of explaining the polar and mildly eccentric orbit of GJ 3470b using two different secular excitation models. The existence of an outer companion can be further constrained with additional RV observations, Gaia astrometry, and future high-contrast imaging observations. Lastly, we show that tidal heating from GJ 3470b’s mild eccentricity has most likely inflated the radius of GJ 3470b by a factor of ∼1.5–1.7, which could help account for its evaporating atmosphere.