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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. 

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. 

Abstract We present a ground-based transit detection of HIP 41378 f, a long-period (P= 542 days), extremely low-density (0.09 ± 0.02 g cm⁻³) giant exoplanet in a dynamically complex system. Using photometry fromTierras, TRAPPIST-North, and multiple Las Cumbres Observatory Global Telescope sites, we constrain the transit center time toT_C,6 = 2460438.891 ± 0.052 BJD TDB. This marks only the second ground-based detection of HIP 41378 f, currently the longest-period and longest-duration transiting exoplanet observed from the ground. We use this new detection, along with a recently published transit time from Rossiter–McLaughlin observations, to update the transit timing variation (TTV) solution for HIP 41378 f. We predict the next two transits will occur at $T_{C,7}=2460980.793_{-0.129}^{+0.098}$BJD TDB (2025 November 1) and $T_{C,8}=2461522.653_{-0.238}^{+0.213}$BJD TDB (2027 April 27). Incorporating new TESS Sector 88 data, we also rule out the 101 days orbital period alias for HIP 41378 d, and find that the remaining viable solutions are centered on the 278, 371, and 1113 days aliases. The latter two imply dynamical configurations that challenge the canonical view of planet e as the dominant perturber of planet f. Our results suggest that HIP 41378 d may instead play the leading role in shaping the TTV of HIP 41378 f. 

Abstract We measure the true obliquity of TOI-2364, a K dwarf with a sub-Saturn-mass (M_p = 0.18M_J) transiting planet on the upper edge of the hot-Neptune desert. We used new Rossiter–McLaughlin observations gathered with the Keck Planet Finder to measure the sky-projected obliquityλ = 7° + 10°–11°. Combined with a stellar rotation period of 23.47 ± 0.29 days measured with photometry from theTierrasObservatory, this yields a stellar inclination of 90° ± 13° and a true obliquityψ = 15 $\stackrel{\text{°}}{.}$6 + 7 $\stackrel{\text{°}}{.}$7–7 $\stackrel{\text{°}}{.}$3, indicating that the planet’s orbit is well aligned with the rotation axis of its host star. The determination ofψis important for investigating a potential bimodality in the orbits of short-period sub-Saturns around cool stars, which tend to be either aligned with or perpendicular to their host stars’ spin axes. 

Abstract Young planets with mass measurements are particularly valuable in studying atmospheric mass-loss processes, but these planets are rare and their masses difficult to measure due to stellar activity. We report the discovery of a planetary system around TOI-6109, a young, 75 Myr-old Sun-like star in the Alpha Persei cluster. It hosts at least two transiting Neptune-like planets within 10 day orbital periods. Using three TESS sectors, 30 CHEOPS orbits, and photometric follow-up observations from the ground, we confirm the signals of the two planets. TOI-6109 b has an orbital period ofP= $5.6904_{-0.0004}^{+0.0004}$days and a radius ofR= $4.87_{-0.12}^{+0.16}$R_⊕. The outer planet, TOI-6109 c has an orbital period ofP= $8.5388_{-0.0005}^{+0.0006}$days and a radius ofR= $4.83_{-0.06}^{+0.07}$R_⊕. These planets orbit just outside a 3:2 mean motion resonance. The near-resonant configuration presents the opportunity to measure the planet’s mass via TTV measurements and to bypass difficult RV measurements. Measuring the masses of the planets in this system will allow us to test theoretical models of atmospheric mass loss. 

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.