Juan I. Espinoza-Retamal

Stellar obliquities provide important clues as to the formation and migration histories of planetary systems, but measurements remain scarce for Neptune-mass planets, especially those orbiting hot stars (above the Kraft break). Here we present observations of the Rossiter–McLaughlin (RM) effect in the hot-star/hot-Neptune system WASP-195 ( T _eff = 6470 ± 100 K, v sin i ⋆ = 10.5 ± 1.1 km s ⁻¹ ) obtained with the Keck Planet Finder and NEID spectrographs. A joint analysis of these observations, archival photometry, and archival radial velocities yields a sky-projected stellar obliquity of λ = −10° ± 7°, consistent with spin–orbit alignment. This makes WASP-195 one of the few hot-star/hot-Neptune systems with a measured obliquity. Archival radial velocities from SOPHIE exclude Jupiter-mass planets within approximately 3 au at 5 σ confidence. The aligned and nearly circular orbit is naturally consistent with a history of disk-driven migration, although coplanar high-eccentricity migration or Roche-lobe overflow cannot be ruled out. We also investigate why so few Neptunes around hot stars have measured obliquities. Their scarcity likely reflects a combination of the lower intrinsic occurrence of short-period Neptunes around hot stars and the difficulty of confirming planet candidates in this regime, where rapid stellar rotation broadens spectral lines and hampers conventional radial-velocity confirmation. Rapid rotation also increases the detectability of the RM effect, a feature that could help to widen the planet confirmation bottleneck while expanding the obliquity census of small planets around hot stars.

Ever since their discovery, hot Jupiters have been one of the most studied types of exoplanets to exist thanks to their significant size, their proximity to their host star, and their significant departure from anything present in our solar system. Yet, the details of their formation and evolution remain unclear, including their connection, if any, to the wider-orbiting warm-Jupiter population. In this work, we present the discovery of K2-232c, an eccentric cold Jupiter ( P = 195 0 − 120 + 140 days, e = 0.35 2 − 0.076 + 0.095 , M sin i = 5.3 1 − 0.45 + 0.48 M J ) companion in a known warm Jupiter ( P = 11.1684377 ± 0.0000010 days, e = 0.24 5 − 0.024 + 0.023 , M = 0.42 7 − 0.036 + 0.039 M J ) system. Placing this system in context with the literature, we find that cold-Jupiter eccentricities are generally higher in hot-Jupiter systems as compared to warm-Jupiter systems, suggesting the formation of hot Jupiters is more dynamically violent than warm Jupiters. This adds further evidence to the claim that these two populations are independent from one another with cold Jupiters appearing to play a crucial role in shaping the formation of both.

We present the first results from the POSEIDON survey, aimed at constraining the dynamical origins of transiting Neptunes through stellar obliquity measurements. We report Rossiter–McLaughlin observations of two Neptunes, TOI-181 b and TOI-883 b, obtained with high-resolution spectroscopy from Magellan/Planet Finder Spectrograph and WIYN/NEID. TOI-181 b is on a 4.5-day orbit with a sky-projected spin–orbit misalignment λ = 32 . ° 0 − 6. ° 5 + 6. ° 3 and a low eccentricity ( e < 0.12 with 2 σ confidence). TOI-883 b has a longer orbital period of 10 days with λ = 2 2 ° − 14 ° + 15 ° and eccentricity e = 0.16 ± 0.03. The significant misalignment of TOI-181 b and the significant eccentricity of TOI-883 b are suggestive of high-eccentricity migration for both systems. After adding these and other new measurements to the sample, we analyze the obliquity distribution of the host stars of transiting Neptunes. Earlier studies had suggested that the obliquity distribution is bimodal, with peaks corresponding to aligned orbits and polar orbits; the addition of more measurements has weakened the evidence for bimodality. The current sample appears to be consistent with a population of well-aligned systems and a smaller population with nearly random obliquities. This distribution resembles that observed for more massive planets, suggesting that transiting Jupiters and Neptunes originate from similar dynamical processes.

We present an observation of the Rossiter–McLaughlin effect for the TOI-1710 system with the NEID spectrograph on the WIYN 3.5 m telescope. The system hosts a warm Neptune ( P ∼ 24 days), and our observations reveal that it orbits in the direction opposite to the stellar spin, with a sky-projected obliquity λ = 179° ± 19°. Combined with information about the rotation period of the host star, we measure a true obliquity ψ = 15 8 − 13 + 11 ° . The host star has an M dwarf companion at a separation of ∼3600 au, but this companion is too distant to be solely responsible for misaligning the warm Neptune. The host star also shows a long-term radial velocity trend, indicative of a companion at intermediate separations. We show that such a companion can dynamically couple the warm Neptune to the distant M dwarf, enabling the transfer of inclination from the wide binary orbit to the planetary orbit. Assuming this scenario is correct, we predict the intermediate companion is a ∼5 M _J planet on a ∼15 au orbit that is nearly aligned with the transiting planet’s orbit.

We present the analysis of five long-period TESS Objects of Interest (TOIs), , with orbital periods exceeding one month. Initially identified by the Transiting Exoplanet Survey Satellite (TESS), we extensively monitored these targets with the Antarctic Search for Transiting Exoplanets (ASTEP), supported by other facilities in the TESS Follow-up Observing Program (TFOP) network. all orbiting Sun-like stars These targets occupy a relatively underexplored region of the period-radius parameter space, offering valuable primordial probes for planetary formation and migration as warm planets better maintain their evolutionary fingerprints. To characterise these systems, we leveraged high-resolution speckle imaging to search for nearby stellar companions, and refine stellar parameters using both reconnaissance spectroscopy and spectral energy distribution (SED) fitting. We combined TESS photometry with high-precision ground-based observations from ASTEP, and when available, included additional photometry and radial velocity data. We applied statistical validation to assess the planetary nature of each candidate and used to jointly model the photometric and spectroscopic datasets. We validate the planetary nature of three TOIs, including the two warm Saturns TOI-4507,b (8.2, 104,d) and TOI-3457,b (10.0, 32.6,d), as well as the warm sub-Neptune TOI-707,b (2.4, eclipsing binaries, namely TOI-2404 and TOI-4404. 52.8,d). The remaining two candidates are most consistent with These results help populate the sparse regime of warm planets, which serve as key tracers of planetary evolution, and demonstrate ASTEP’s effectiveness as a ground-based follow-up instrument for long-period systems.

The population of short-period exo-Neptunes is thought to be shaped by an interplay between different dynamical mechanisms, such as orbital migration and tidal effects, and photoevaporation. We can gain insight into these processes by studying observables such as the stellar obliquity. Here we study the Rossiter-McLaughlin (RM) effect and measure the projected obliquity, λ, of the Neptunian ridge planet WASP-156 b. We analyse new ESPRESSO and MAROON-X spectroscopic transit observations, and new NGTS photometry simultaneous to the ESPRESSO data. Our analyses show an aligned orbit (λ = −8 ± 16○, based on the ESPRESSO observations), in contrast to a previous report of a highly misaligned orbit. We also find the star’s projected rotational velocity to be vsin i⋆ ≤ 2 km s−1 from spectral line modelling and vsin i⋆ = 0.40 ± 0.11 km s−1 from the RM modelling. This is lower than the previously reported value of ∼4 km s−1, which could partly explain the previously derived polar orbit. We also update the system’s orbital parameters and rule out Jupiter-mass companions within 5 au using long-term radial velocity data. The planet’s aligned and circular orbit (e < 0.16 at 3σ), and lack of nearby massive companions, are consistent with in situ formation or early disc-driven migration. Our findings move WASP-156 b from a tentative cluster of close-in Neptunes in polar orbits to the group of aligned Neptunes.

The evolution of one member of a stellar binary into a white dwarf has been proposed as a mechanism that triggers the formation of close-in gas giant planets. The star’s asymmetric mass loss during the Asymptotic Giant Branch stage gives it a velocity recoil or “kick” that can initiate eccentric Lidov–Kozai oscillations, potentially causing a planet around the secondary star to migrate inward and perturb the eccentricity and inclination of its orbit. Here we present a measurement of the stellar obliquity of TOI-1259Ab, a gas giant in a close-in orbit around a K star with a white dwarf companion about 1650 au away. By using the NEID spectrograph to detect the Rossiter-McLaughlin effect during the planetary transit, we find the sky-projected obliquity to be λ = 7 ₋₂₁ ^+20° . When combined with estimates of the stellar rotation period, radius, and projected rotation velocity, we find the true 3D obliquity to be ψ = 24 ₋₁₂ ^+14° ( ψ < 47 ° at 95% confidence), revealing that the orbit of TOI-1259Ab is on a low-obliquity orbit with respect to the star’s equatorial plane. Because the planet’s orbit is too wide for tidal realignment to be expected, TOI-1259Ab might have formed quiescently in this low-obliquity configuration. Alternatively, as we show with dynamical simulations, eccentric Lidov–Kozai oscillations triggered by the evolution of the binary companion expect to lead to a low-obliquity configuration with a probability of ∼14%.

We present the discovery and confirmation of the ultrashort period (USP) planet TOI-2431 b orbiting a nearby ( d ~ 36 pc) late K star ( T _eff = 4109 ± 28 K) using observations from the Transiting Exoplanet Survey Satellite (TESS), precise radial velocities (RVs) with NEID and Habitable-zone Planet Finder (HPF) spectrographs, as well as ground-based high-contrast imaging from NESSI. TOI-2431 b has a period of 5 hours and 22 minutes, making it one of the shortest-period exoplanets known to date. TOI-2431 b has a radius of 1.534 ± 0.033 R _⊕ and a mass of 6.2 ± 1.6 M _⊕ , where the exact mass precision shows a slight dependence on the choice of prior. This suggests TOI-2431 b has a density compatible with an Earth-like composition and due to its high irradiation, it is likely to be a “lava-world” with a T _eq = 2063 ± 30 K. We estimate that the current orbital period is only 30% larger than the Roche-limit orbital period and that it has an expected orbital decay timescale of only ~31 Myr. Finally, due to the brightness of the host star ( V = 10.9, K = 7.6), we find that TOI-2431 b has a high emission spectroscopy metric (ESM) of 27, making it one of the best USP systems for atmospheric phase-curve analyses.

Recent observations with the LOw Frequency ARray (LOFAR) have revealed 19 nearby M dwarfs showing bright circularly polarized radio emission. One of the possible sources of such emission is through magnetic star-planet interactions (MSPIs) with unseen close-in planets. We present the initial results from a spectroscopic survey with the Habitable-zone Planet Finder (HPF) and NEID spectrographs designed to characterize this sample and further investigate the origin of the radio emission. We provide four new insights into the sample. I) We uniformly characterized the stellar properties, constraining their effective temperatures ( T _eff ), surface gravities (log g ), metallicities ([Fe/H]), projected rotational velocities ( v sin i _⋆ ), rotation periods ( P _rot ), stellar radii ( R _⋆ ), and stellar inclinations ( i _⋆ ) where possible. Further, from a homogeneous analysis of the HPF spectra, we inferred their chromospheric activity and spectroscopic multiplicity states. From this, we identified GJ 625, GJ 1151, and LHS 2395 as single, quiescent stars amenable to precise radial velocity follow-up, making them strong MSPI candidates. II) We show that the distribution of stellar inclinations are compatible with an isotropic distribution, providing no evidence for a preference to pole-on configurations. III) We refined the radial velocity solution for GJ 625 b, the only currently known close-in planet in the sample, reducing the uncertainty in its orbital period by a factor of three, to facilitate future phase-dependent radio analysis. IV) Finally, we identified GJ 3861 as a spectroscopic binary with an orbital period of P = 14.841181 _−0.00010 ^+0.00011 d and with a mass ratio of q = 0.7663 _−0.0018 ^+0.0020 , making it the only confirmed binary with a relatively short orbit in the sample, where we surmise the radio emission is likely related to magnetospheric interactions between the two stars. These results advance our understanding of radio-emitting M dwarfs and establish an observational foundation for identifying MSPIs.