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1. The OATMEAL Survey. II. The 3D Spin–Orbit Obliquity of an Eccentric Transiting Brown Dwarf in the Ruprecht 147 Open Cluster

   https://doi.org/10.3847/1538-3881/ae19e8  

   Carmichael, Theron W; Giacalone, Steven; Vowell, Noah; Huber, Daniel; Wang, Xian-Yu; Bossett, Malik; Handley, Luke; Householder, Aaron; Li, Yaguang; Fulton, Benjamin J; et al (December 2025, The Astronomical Journal)

   Abstract We present a new analysis of the CWW 89 system as part of the Orbital Architectures of Transiting Massive Exoplanets And Low-mass stars (OATMEAL) survey. The CWW 89 system is a member of the 2.8 Gyr old Ruprecht 147 (NGC 6774) cluster and consists of two stars, CWW 89A (EPIC 219388192) and CWW 89B, with the primary hosting a transiting brown dwarf, CWW 89Ab. We use in-transit, highly precise radial velocity measurements with the Keck Planet Finder to characterize the Rossiter–McLaughlin (RM) effect and measure the projected spin–orbit obliquity ∣λ∣ = 1 $\stackrel{\text{°}}{.}$ 4 ± 2 $\stackrel{\text{°}}{.}$ 5 and the full 3D spin–orbit obliquity of the brown dwarf to be $\psi =15.1_{-10.9}^{+15.0^{\circ }}$ . This value ofλimplies that the brown dwarf’s orbit is prograde and well-aligned with the equator of the host star, continuing the trend of transiting brown dwarfs showing a preference for spin–orbit alignment (λ ≈ 0°) regardless of the stellar effective temperature. This contrast with the transiting giant planet population, whose spin–orbit alignments depend on hostT_eff, shows an increasingly clear distinction in the formation and orbital migration mechanisms between transiting giant planets and transiting brown dwarfs like CWW 89Ab. For this system in particular, we find it plausible that the brown dwarf may have undergone coplanar high-eccentricity migration influenced by CWW 89B. 

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2. Searching for GEMS: Discovery and Characterization of Two Brown Dwarfs Around M Dwarfs*

   https://doi.org/10.3847/1538-3881/adbb54  

   Larsen, Alexander; Swaby, Tera N; Kobulnicky, Henry A; Cañas, Caleb I; Kanodia, Shubham; Libby-Roberts, Jessica; Monson, Andrew; Gupta, Arvind F; Cochran, William; Mahadevan, Suvrath; et al (April 2025, The Astronomical Journal)

   Abstract Brown dwarfs bridge the gap between stars and planets, providing valuable insight into both planetary and stellar-formation mechanisms. Yet the census of transiting brown-dwarf companions, in particular around M-dwarf stars, remains incomplete. We report the discovery of two transiting brown dwarfs around low-mass hosts using a combination of space- and ground-based photometry along with near-infrared radial velocities. We characterize TOI-5389Ab ( $68.0_{-2.2}^{+2.2}{M}_{\mathrm{J}}$ ) and TOI-5610b ( $40.4_{-1.0}^{+1.0}{M}_{\mathrm{J}}$ ), two moderately massive brown dwarfs orbiting early M-dwarf hosts (T_eff = 3569 ± 59 K and 3618 ± 59 K, respectively). For TOI-5389Ab, the best fitting parameters are periodP = 10.40046 ± 0.00002 days, radius $R_{\mathrm{BD}}=0.824_{-0.031}^{+0.033}$ R_J, and low eccentricity $e=0.0962_{-0.0046}^{+0.0027}$ . In particular, this constitutes one of the most extreme substellar-stellar companion-to-host mass ratios ofq= 0.150. For TOI-5610b, the best-fitting parameters are periodP = 7.95346 ± 0.00002 days, radius $R_{\mathrm{BD}}=0.887_{-0.031}^{+0.031}$ R_J, and moderate eccentricity $e=0.354_{-0.012}^{+0.011}$ . Both targets are expected to have shallow, but potentially observable, occultations: ≲500 ppm in the JohnsonKband. A statistical analysis of M-dwarf/BD systems reveals for the first time that those at short orbital periods (P < 13 days) exhibit a dearth of 13M_J < M_BD < 40M_Jcompanions (q < 0.1) compared to those at slightly wider separations. 

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3. The Aligned Orbit of a Hot Jupiter around the M Dwarf TOI-4201

   https://doi.org/10.3847/2041-8213/ad5967  

   Gan, Tianjun; Wang, Sharon X; Dai, Fei; Winn, Joshua N; Mao, Shude; Xu, Siyi; Pallé, Enric; Bean, Jacob L; Brady, Madison; Brown, Nina; et al (July 2024, The Astrophysical Journal Letters)

   Abstract Measuring the obliquities of stars hosting giant planets may shed light on the dynamical history of planetary systems. Significant efforts have been made to measure the obliquities of FGK stars with hot Jupiters, mainly based on observations of the Rossiter–McLaughlin effect. In contrast, M dwarfs with hot Jupiters have hardly been explored because such systems are rare and often not favorable for such precise observations. Here, we report the first detection of the Rossiter–McLaughlin effect for an M dwarf with a hot Jupiter, TOI-4201, using the Gemini-North/MAROON-X spectrograph. We find TOI-4201 to be well aligned with its giant planet, with a sky-projected obliquity of $\lambda =-{3.0}_{-3.2}^{+3.7}°$ and a true obliquity of $\psi ={21.3}_{-12.8}^{+12.5}°$ with an upper limit of 40^◦at a 95% confidence level. The result agrees with dynamically quiet formation or tidal obliquity damping that realigned the system. As the first hot Jupiter around an M dwarf with its obliquity measured, TOI-4201b joins the group of aligned giant planets around cool stars (T_eff< 6250 K), as well as the small but growing sample of planets with relatively high planet-to-star mass ratio (M_p/M_*≳ 3 × 10⁻³) that also appear to be mostly aligned. 

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4. Stellar Obliquities of Young Systems, Atmospheres Undergoing Contraction and Escape (SOYSAUCE): A Likely Aligned Orbit for the 3 Myr Planet TIDYE-1 b

   https://doi.org/10.3847/2041-8213/ae2004  

   Barber, Madyson G; Mann, Andrew W; Johnson, Marshall C; Mori, Mayuko; Livingston, John; Krolikowski, Daniel M; Narita, Norio; Fukui, Akihiko; Hirano, Teruyuki; Vanderburg, Andrew; et al (November 2025, The Astrophysical Journal Letters)

   Abstract Despite the wide range of planet–star (mis)alignments in the mature population of transiting exoplanets, the small number of known young transiting planets are nearly all aligned with the rotation axes of their host stars, as determined by the sky-projected obliquity angle. The small number of young systems with measured obliquities limits statistical conclusions. Here we determine the sky-projected obliquity (λ) of the 3 Myr transiting planet with a misaligned outer protoplanetary disk, TIDYE-1 b (IRAS 04125+2902b), using the Rossiter–McLaughlin (RM) effect. Our dataset lacks a pretransit baseline and ingress, complicating a blind RM fit. Instead, we use contemporaneous spectra and photometry from a mass-measurement campaign to model the stellar activity trend across the transit and provide an external prior on the velocity baseline. We determine $\mid \lambda \mid =11.8_{-5.0}^{+5.9}°$ . Combined with the published rotational velocity of the star, we find a true three-dimensional obliquity of $\psi =15.2_{-5.7}^{+7.3}°$ . Our result is consistent with an aligned orbit, suggesting the planet remains aligned to its star even though the outer disk is misaligned, though additional RM observations are needed to exclude the low-probability tail of misaligned (>30°) scenarios present in our posterior. 

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5. TOI-5344 b: A Saturn-like Planet Orbiting a Super-solar Metallicity M0 Dwarf

   https://doi.org/10.3847/1538-3881/ad09c2  

   Han, Te; Robertson, Paul; Kanodia, Shubham; Cañas, Caleb; Lin, Andrea S.; Stefánsson, Gumundur; Libby-Roberts, Jessica E.; Larsen, Alexander; Kobulnicky, Henry A.; Mahadevan, Suvrath; et al (December 2023, The Astronomical Journal)

   Abstract We confirm the planetary nature of TOI-5344 b as a transiting giant exoplanet around an M0-dwarf star. TOI-5344 b was discovered with the Transiting Exoplanet Survey Satellite photometry and confirmed with ground-based photometry (the Red Buttes Observatory 0.6 m telescope), radial velocity (the Habitable-zone Planet Finder), and speckle imaging (the NN-Explore Exoplanet Stellar Speckle Imager). TOI-5344 b is a Saturn-like giant planet (ρ= 0.80 ${}_{-0.15}^{+0.17}$ g cm⁻³) with a planetary radius of 9.7 ± 0.5R_⊕(0.87 ± 0.04R_Jup) and a planetary mass of ${135}_{-18}^{+17}{M}_{\oplus }$ (0.42 ${}_{-0.06}^{+0.05}{M}_{\mathrm{Jup}}$ ). It has an orbital period of ${3.792622}_{-0.000010}^{+0.000010}$ days and an orbital eccentricity of ${0.06}_{-0.04}^{+0.07}$ . We measure a high metallicity for TOI-5344 of [Fe/H] = 0.48 ± 0.12, where the high metallicity is consistent with expectations from formation through core accretion. We compare the metallicity of the M-dwarf hosts of giant exoplanets to that of M-dwarf hosts of nongiants (≲8R_⊕). While the two populations appear to show different metallicity distributions, quantitative tests are prohibited by various sample caveats. 

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