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1. Spot-crossing Variations Confirm a Misaligned Orbit for a Planet Transiting an M Dwarf

   https://doi.org/10.3847/1538-3881/adf72f  

   Tamburo, Patrick; Yee, Samuel W; García-Mejía, Juliana; Charbonneau, David; Bieryla, Allyson; Collins, Karen A; Shporer, Avi (September 2025, The Astronomical Journal)

   Abstract TOI-3884 b is an unusual 6.4R_⊕planet orbiting an M4 host, whose transits display large and persistent spot-crossing events. We used theTierrasObservatory to monitor both the long-term photometric variability of TOI-3884 and changes in the spot-crossing events across multiple transits of the planet. We show that the star rotates with a period of 11.020 ± 0.015 days. We simultaneously model the rotational modulation of the star and variations in transit shapes that arise due to rotation of the spot, allowing us to determine the true stellar obliquity,ψ_⋆. The data are best described by a planet on a misaligned orbit around a highly inclined star (ψ_⋆ =  ${77\stackrel{\text{°}}{.}4}_{-2\stackrel{\text{°}}{.}5}^{+2\stackrel{\text{°}}{.}3}$ ;i_⋆ =  ${22\stackrel{\text{°}}{.}3}_{-1\stackrel{\text{°}}{.}6}^{+1\stackrel{\text{°}}{.}8}$ ) that hosts a large polar starspot (r_spot =  ${31.2^{\circ }}_{-1.9^{\circ }}^{+2.4^{\circ }}$ ;λ_spot =  80 $\stackrel{\text{°}}{.}$ 5 ± 1 $\stackrel{\text{°}}{.}$ 2). Archival photometry from the Zwicky Transient Facility suggests that this polar spot has persisted on TOI-3884 for at least seven years. The TOI-3884 system provides a benchmark for studying the evolution of a polar spot on an M dwarf. 

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2. 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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3. The Polar Orbit of TOI-2374 b, a Planet in the Neptunian Ridge

   https://doi.org/10.3847/1538-3881/ae070b  

   Yee, Samuel W; Tamburo, Patrick; Stefánsson, Gudmundur; García-Mejía, Juliana; Charbonneau, David; Barkaoui, Khalid; Collins, Karen A; Schwarz, Richard P; Narita, Norio; Fukui, Akihiko; et al (October 2025, The Astronomical Journal)

   Abstract The “Neptunian ridge” is a recently identified peak in the frequency of planets with sizes between that of Neptune and Saturn orbiting their host stars with periods between 3 and 6 days. These planets may have formed similarly to their larger, hot Jupiter counterparts in the “3 day pileup,” through a dynamically excited migration pathway. The distribution of stellar obliquities in hot Neptune systems may therefore provide a vital clue as to their origin. We report a new stellar obliquity measurement for TOI-2374b, a planet in the Neptunian ridge (P= 4.31 days,R_p = 7.5R_⊕). We observed a spectroscopic transit of TOI-2374b with the Keck Planet Finder, detecting the Rossiter–McLaughlin (RM) anomaly with an amplitude of 3 m s⁻¹, and measured a sky-projected obliquity of $\lambda ={81°}_{-22^{\circ }}^{+23^{\circ }}$ , indicating an orbit significantly misaligned with the spin axis of its host star. A reloaded RM analysis of the cross-correlation functions confirms this misalignment, measuring $\lambda ={65°}_{-24^{\circ }}^{+32^{\circ }}$ . Additionally, we measured a stellar rotation period of $P_{\mathrm{rot}}=26.4_{-0.8}^{+0.9}$ days with photometry from theTierrasobservatory, allowing us to deduce the three-dimensional stellar obliquity of $\psi ={85\stackrel{°}{.}9}_{-9\stackrel{°}{.}2}^{+8\stackrel{°}{.}6}$ . TOI-2374b joins a growing number of hot Neptunes on polar orbits. The high frequency of misaligned orbits for Neptunian ridge and desert planets, compared with their longer period counterparts, is reminiscent of patterns seen for the giant planets and may suggest a similar formation mechanism. 

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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. 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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