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Two leading hypotheses for hot Jupiter migration are disk migration and high-eccentricity migration (HEM). Stellar obliquity is commonly used to distinguish them, as high obliquity often accompanies HEM. However, low obliquity does not guarantee disk migration, due to possible spin–orbit realignment or coplanar HEM. Seeking a proxy for disk migration, we investigate the idea that when the circularization timescale of a planet on circular orbit is longer than its age (τcir > τage), HEM would not have had sufficient time to complete, favoring disk migration. We empirically calibrate the reduced planetary tidal quality factor to be Qp=4.9−2.5+3.5×105 using the eccentricity distribution of 500+ Jovian mass (0.2MJ < Mp < 13MJ) planets with measured masses and radii, a value consistent with solar system Jupiter. We then calculate τcir and identify dozens of disk migration candidates (τcir > τage, e < 0.1). These planets show three notable trends. We first find a clear cutoff of obliquity at τcir ∼ τage, suggesting the primordial alignment of protoplanetary disks. Second, we find that among hot Jupiters (a < 0.1 au), nearby companions are preferentially found around disk migration candidates, suggesting that either HEM dominates hot Jupiter formation, or disk migration also disrupts nearby companions at short separations. Finally, we find a possible dearth of disk migration candidates around mass ratio logq∼−3.2 , consistent with a similar dip suggested at longer orbits from microlensing. The lack of planets across different orbital distance, if true, could be interpreted as a hint of runaway migration.

One of the possible signs of life on distant habitable exoplanets is the red-edge, which is a rise in the reflectivity of planets between visible and near-infrared (NIR) wavelengths. Previous studies suggested the possibility that the red-edge position for habitable exoplanets around M-dwarfs may be shifted to a longer wavelength than that for Earth. We investigated plausible red-edge position in terms of the light environment during the course of the evolution of phototrophs. We show that phototrophs on M-dwarf habitable exoplanets may use visible light when they first evolve in the ocean and when they first colonize the land. The adaptive evolution of oxygenic photosynthesis may eventually also use NIR radiation, by one of two photochemical reaction centers, with the other center continuing to use visible light. These “two-color” reaction centers can absorb more photons, but they will encounter difficulty in adapting to drastically changing light conditions at the boundary between land and water. NIR photosynthesis can be more productive on land, though its evolution would be preceded by the Earth-type vegetation. Thus, the red-edge position caused by photosynthetic organisms on habitable M-dwarf exoplanets could initially be similar to that on Earth and later move to a longer wavelength.

The youngest (<50 Myr) planets are vital to understand planet formation and early evolution. The 17 Myr system HIP 67522 is already known to host a giant (≃10R ⊕) planet on a tight orbit. In their discovery paper, Rizzuto et al. reported a tentative single-transit detection of an additional planet in the system using TESS. Here, we report the discovery of HIP 67522c, a 7.9 R ⊕ planet that matches with that single-transit event. We confirm the signal with ground-based multiwavelength photometry from Sinistro and MuSCAT4. At a period of 14.33 days, planet c is close to a 2:1 mean-motion resonance with b (6.96 days or 2.06:1). The light curve shows distortions during many of the transits, which are consistent with spot-crossing events and/or flares. Fewer stellar activity events are seen in the transits of planet b, suggesting that planet c is crossing a more active latitude. Such distortions, combined with systematics in the TESS light-curve extraction, likely explain why planet c was previously missed.

Spot-crossing transits offer a unique opportunity to probe spot properties such as temperature, size, and surface distribution. TOI-3884 is a rare system in which spot-crossing features are persistently observed during every transit. This is due to its unusual configuration: a nearly polar-orbit super-Neptune transits a pole-on mid-M dwarf, repeatedly crossing a polar spot. However, previous studies have reported discrepant values in key system parameters, such as stellar inclination and obliquity. To address this, we conducted multiband, multiepoch transit observations of TOI-3884 b using the MuSCAT instrument series, along with photometric monitoring with the Las Cumbres Observatory 1 m telescopes/Sinistro. We detected time-dependent variations in the spot-crossing signals, indicating that the spot is not exactly on the pole. From the monitoring data, we measured a stellar rotation period of 11.043−0.053+0.054 days with a modulation amplitude of ∼5% in the r band, consistent with the time variability in the spot-crossing features. Our analysis reconciles previous discrepancies and improves the constraints on the parameters of the system geometry ( i⋆=139.9−2.0+1.2 deg and λ=41.0−9.0+3.7 deg) and those of the spot properties (spot radius of 0.425−0.011+0.018R⋆ and a spot–photosphere temperature difference of 200−9+11 K). These results provide a critical context for interpreting upcoming transmission spectroscopy of TOI-3884 b, as well as yielding new insights into the magnetic activity and spin–orbit geometry of M dwarfs.

We present the Rossiter–McLaughlin measurement of the sub-Neptune TOI-1759A b with MAROON-X. A joint analysis with MuSCAT3 photometry and nine additional TESS transits produces a sky-projected obliquity of ∣λ∣ = 4° ± 18°. We also derive a true obliquity of ψ = 24° ± 12° making this planet consistent with full alignment albeit to <1σ. With a period of 18.85 days and an a/R* of 40, TOI-1759A b is the longest period single sub-Neptune to have a measured obliquity. It joins a growing number of smaller planets which have had this measurement made and, along with K2-25 b, is the only single, aligned sub-Neptune known to date. We also provide an overview of the emerging distribution of obliquity measurements for planets with R < 8 R⊕. We find that these types of planets tend toward alignment, especially the sub-Neptunes and super-Earths, implying a dynamically cool formation history. The majority of misaligned planets in this category have 4 < R ≤ 8 R⊕ and are more likely to be isolated than planets rather than in compact systems. We find this result to be significant at the 3σ level, consistent with previous studies. In addition, we conduct injection and recovery testing on available archival radial velocity data to put limits on the presence of massive companions in these systems. Current archival data is insufficient for most systems to have detected a giant planet.

It is relatively rare for gas giant planets to have resonant or near-resonant companions, but these systems are particularly useful for constraining planet formation and migration models. In this study, we examine Kepler-1624b, a sub-Saturn orbiting an M dwarf that was previously found to exhibit transit timing variations (TTVs) with an amplitude of approximately 2 minutes, suggesting the presence of a nearby nontransiting companion. We reanalyze the transits from archival Kepler data and extend the TTV baseline by 11 yr by combining TESS data with three new ground-based transit observations from Palomar and Las Cumbres Observatories. We jointly fit these datasets and find that the TTV amplitude is significantly weaker in our updated analysis. We calculate the Bayes factor for a one-planet versus two-planet model and find that the one-planet model is preferred. Our results highlight the need for careful analysis of systems with relatively low amplitude TTV signals that are identified in large automated catalogs.

Detailed chemical analyses of M dwarfs are scarce but necessary to constrain the formation environment and internal structure of planets being found around them. We present elemental abundances of 13 M dwarfs (2900 < T eff < 3500 K) observed in the Subaru/IRD planet search project. They are mid- to late-M dwarfs whose abundance of individual elements has not been well studied. We use the high-resolution (∼70,000) near-infrared (970–1750 nm) spectra to measure the abundances of Na, Mg, Si, K, Ca, Ti, V, Cr, Mn, Fe, and Sr by the line-by-line analysis based on model atmospheres, with typical errors ranging from 0.2 dex for [Fe/H] to 0.3–0.4 dex for other [X/H]. We measure radial velocities from the spectra and combine them with Gaia astrometry to calculate the Galactocentric space velocities UVW. The resulting [Fe/H] values agree with previous estimates based on medium-resolution K-band spectroscopy, showing a wide distribution of metallicity (−0.6 < [Fe/H] < +0.4). The abundance ratios of individual elements [X/Fe] are generally aligned with the solar values in all targets. While the [X/Fe] distributions are comparable to those of nearby FGK stars, most of which belong to the thin-disk population, the most metal-poor object, GJ 699, could be a thick-disk star. The UVW velocities also support this. The results raise the prospect that near-infrared spectra of M dwarfs obtained in the planet search projects can be used to grasp the trend of elemental abundances and the Galactic stellar population of nearby M dwarfs.

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, Rp = 7.5 R⊕). 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 λ=81°−22∘+23∘ , 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 λ=65°−24∘+32∘ . Additionally, we measured a stellar rotation period of Prot=26.4−0.8+0.9 days with photometry from the Tierras observatory, allowing us to deduce the three-dimensional stellar obliquity of ψ=85.°9−9.°2+8.°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.

As the intermediate-mass siblings of stars and planets, brown dwarfs (BDs) are vital to study for a better understanding of how objects change across the planet-to-star mass range. Here, we report two low-mass transiting BD systems discovered by TESS, TOI-4776 (TIC 196286578) and TOI-5422 (TI 80611440), located in an underpopulated region of the BD mass–period space. These two systems have comparable masses but different ages. The younger and larger BD is TOI-4776 b with 32.3−1.7+1.8MJup and 1.01 ± 0.05 RJup, orbiting a late-F star about 4.7−2.5+3.1 Gyr old in an ∼10.41 day period. The older TOI-5422 b has 28.0−1.2+1.6MJup and 0.81 ± 0.03 RJup in an ∼5.38 day orbit around a subgiant star about 7.6−2.6+2.5 Gyr old. Compared with substellar mass–radius evolution models, TOI-4776 b has an inflated radius. In contrast, TOI-5422 b is slightly “underluminous” with respect to model predictions, which is not commonly seen in the BD population. In addition, TOI-5422 shows apparent photometric modulations with a rotation period of 10.8 ± 0.5 days found by rotation analysis, and the stellar inclination angle is obtained to be I⋆=76−12+10 deg. Therefore, it is likely that TOI-5422 b is spinning up the host star and its orbit is aligned with the stellar spin axis.

M-dwarf stars provide us with an ideal opportunity to study nearby small planets. The HUnting for M Dwarf Rocky planets Using MAROON-X (HUMDRUM) survey uses the MAROON-X spectrograph, which is ideally suited to studying these stars, to measure precise masses of a volume-limited (<30 pc) sample of transiting M-dwarf planets. TOI-1450 is a nearby (22.5 pc) binary system containing a M3 dwarf with a roughly 3000 K companion. Its primary star, TOI-1450A, was identified by the Transiting Exoplanet Survey Satellite (TESS) to have a 2.04 days transit signal, and is included in the HUMDRUM sample. In this paper, we present MAROON-X radial velocities (RVs) which confirm the planetary nature of this signal and measure its mass at nearly 10% precision. The 2.04 days planet, TOI-1450A b, has R b = 1.13 ± 0.04 R ⊕ and M b = 1.26 ± 0.13 M ⊕. It is the second-lowest-mass transiting planet with a high-precision RV mass measurement. With this mass and radius, the planet’s mean density is compatible with an Earth-like composition. Given its short orbital period and slightly sub-Earth density, it may be amenable to JWST follow-up to test whether the planet has retained an atmosphere despite extreme heating from the nearby star. We also discover a nontransiting planet in the system with a period of 5.07 days and a Msinic=1.53±0.18M⊕ . We also find a 2.01 days signal present in the systems’s TESS photometry that likely corresponds to the rotation period of TOI-1450A’s binary companion, TOI-1450B. TOI-1450A, meanwhile, appears to have a rotation period of approximately 40 days, which is in line with our expectations for a mid-M dwarf.