Cristobal Petrovich

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.

Context . The wide cavity in the PDS 70 protoplanetary disk harbors two directly imaged confirmed protoplanets. Several studies have proposed the existence of a third inner planet candidate at ~13 au, labeled as PDS 70 d. While its motion is consistent with a Keplerian orbit, its unusually blue spectrum challenges a planetary interpretation. Aims . We investigated the presence and nature of a third inner planet using new SPHERE and GRAVITY observations. Methods . Using the star-hopping strategy, we obtained new coronagraphic SPHERE/IRDIS observations of PDS 70 in dual-polarization imaging mode in the H band, as well as non-coronagraphic observations with SPHERE/IRDIFS covering the YJHK bands. We also searched for a planetary-like signal using GRAVITY+ in astrometric mode with the four-unit-telescope configuration. Results . We consistently detect two inner emission features with SPHERE: one corresponding to the previously proposed planet candidate at ~13 au and another that appears to share the same orbit but leads it by ~120° (clockwise) with a more elongated morphology. Both features exhibit dust-scattered light spectra while displaying different colors, which may indicate differences in dust grain sizes. We show that such a configuration is consistent with co-orbital dust accumulated at the stable Lagrangian regions of a yet undetected planet, distinct from the previously proposed candidate. The analysis of GRAVITY data at the predicted position of this newly proposed planet has resulted in a marginal (3 σ ) detection located between the two clumps along the same orbit ( ρ = 76.2 ± 0.29 mas, and position angle PA = 226.50 ± 0.21°), and consistent with a ~3 M _Jup planet. This planet-like signal aligns with a narrow shadow detected in the outer disk with SPHERE. Additionally, with SPHERE we detect polarized emission very close to the star, which likely arise from the inner disk, with an inclination of 50° and a PA of ~135°. The fact that the two dust clumps appear embedded within this polarized emission motivates an inner disk-related alternative scenario. Conclusions . We conclude that the emission from the previously reported third planet candidate could arise either from a dust clump trailing a yet undetected planet along the same orbit, or from a rotating substructure within the inner disk. Additional observations are required to further test these two proposed scenarios. In particular, confirming the new GRAVITY planet-like signal would support the use of co-orbital substructures as indirect tracers of embedded planets.

A growing population of short-period Neptune-like planets has nonzero eccentricities and, in some cases, large stellar obliquities, suggestive of high-eccentricity migration. Modeling this evolution requires a prescription for tidal dissipation, which in Neptune-like planets may be dominated by rocky or icy cores rather than by extended gaseous envelopes as often assumed for gas giants. We study the coupled orbital and thermal evolution of eccentric Neptune-like planets whose tidal dissipation is controlled by a viscoelastic Maxwell core. We compute the full harmonic tidal response, follow the equilibrium spin state, and evolve the core temperature; the changing thermal state feeds back on the orbit by modifying the viscosity and hence the frequency-dependent tidal response. We find that the coupled evolution is self-regulated: tidal heating initially drives cold, weakly dissipative cores toward efficient dissipation, but the resulting temperature increase lowers the viscosity, shifts the tidal response toward the fluid-like side of the Maxwell peak, and slows the subsequent migration. This feedback drives the system toward a quasi-steady heating-cooling balance, produces long-lived eccentric phases, and weakens the otherwise steep dependence of circularization time on final orbital distance. Thermally regulated tides therefore offer a natural explanation for how observed hot Neptunes can remain eccentric across a broad range of orbital distances, where a single fixed tidal efficiency would either erase eccentricity too efficiently close in or fail to damp it farther out.

Context. The detection of likely thermal ultraviolet emission from a few old neutron stars suggests that at least one internal heating mechanism is present in these stars. One such proposed mechanism is rotochemical heating, which describes a scenario where the continuous contraction of the neutron star due to its spin-down produces chemical imbalances that induce Urca reactions, resulting in the latter depositing heat in the neutron star core. If the protons in the star are superconducting, their energy gap suppresses the reactions, except in microscopic magnetized regions (such as quantized flux tubes), where the protons act as if they were normal. Therefore, the strength of the internal magnetic field controls the rate at which reactions proceed and thus affects the thermal evolution of the neutron star. Aims. Here, we present the first comprehensive study of the effect of an internal magnetic field in the superconducting interior on rotochemical heating. Methods. We simulated the evolution of neutron stars for different internal magnetic field strengths and neutron energy gaps, and we compared the results to Hubble Space Telescope observations of old neutron stars. Results. Within the proposed model, the observationally inferred temperatures of the millisecond pulsar (MSP) PSR J0437−4715 and the classical pulsar (CP) PSR B0950+08 as well as the upper limits for the MSP PSR J2124−3358 and the CPs PSR J0108−1431 and PSR J2144−3933 can be accounted for if the proton energy gap is large (∼1.5 MeV) and the neutron energy gap is small (≲0.1 MeV) or vanishing, while the MSP PSR J0437−4715 needs to have a very weak internal magnetic field. Conclusions. Our results suggest that rotochemical heating alone can account for the observed thermal emission of old neutron stars if neutron-star cores are characterized by a large proton pairing gap and a small or vanishing neutron gap, and MSPs have very weak internal magnetic fields.

Stellar obliquities provide a fossil record of hot-Jupiter (HJ) migration. An emerging observational trend in single-star systems is that strongly misaligned HJs are largely confined to short orbital periods, while longer-period HJs are preferentially aligned. This pattern cannot be explained by tidal dissipation in the star and may instead preserve clues to the migration pathway. We show that secular high-eccentricity migration driven by a distant planetary companion naturally produces such an obliquity–period correlation. In our simulations, the shortest-period HJs tend to be produced by the von Zeipel–Lidov–Kozai mechanism driven by highly inclined companions, which results in a broad range of final stellar obliquities. The longest-period HJs, on the other hand, are produced over longer timescales by coplanar high-eccentricity migration, which preserves low obliquities. The transition between these two limits is not abrupt, with intermediate-period HJs displaying a moderate range of obliquities. According to this interpretation, we predict that the shortest-period HJs should have distant planetary companions with broadly distributed mutual inclinations, whereas the companions of longer-period HJs should reside in nearly coplanar orbits. Upcoming Gaia astrometric constraints will provide a key test of this picture.

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.

Passively cooling neutron stars (NSs) are expected to reach undetectably low surface temperatures, T _s < 10 ⁴ K, within less than 10 ⁷ yr. However, Hubble Space Telescope (HST) observations have revealed likely thermal ultraviolet emission from the gigayear-old millisecond pulsars PSR J0437−4715 and PSR J2124−3358 and the ∼10 ^7 − 8 year-old classical pulsars PSR B0950+08 and PSR J0108−1431, implying temperatures of T _s ∼ 10 ⁵ K and thus suggesting the presence of some heating mechanism. In this work, the thermal evolution for each of these NSs was computed considering rotochemical heating in the NS core with normal or Cooper-paired matter, vortex creep in the inner crust, and crustal heating through nuclear processes. The results were contrasted with the observations while also including the stringent upper limit on the temperature of PSR J2144−3933. No single heating mechanism alone was found to account for all the observations. The high temperature of PSR J0437−4715 can be explained by rotochemical heating in the presence of a large Cooper pairing gap, Δ _i ∼ 1.5 MeV, for either neutrons or protons (or an equivalent combination of both), but this mechanism would require an unrealistically short initial rotation period, P ₀ ≲ 1.8 ms, to account for the high temperature of the classical pulsar PSR B0950+08. Conversely, the latter can be explained by rotochemical heating with modified Urca reactions in normal matter or by vortex creep with an excess angular momentum parameter, J ∼ 3 × 10 ⁴³ erg s, but these models are insufficient to account for the former. However, a model that includes rotochemical heating with a large Cooper pairing gap together with vortex creep is consistent with the temperature measurements of these two pulsars as well as the upper limits for the other three. Moreover, this scenario predicts that the temperatures of the other three pulsars should be close to these upper limits, suggesting that deeper observations and/or a wider wavelength coverage for these and other old nearby pulsars should yield a strong probe of this model.

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%.

The current populations trapped in Neptune’s main mean motion resonances in the Kuiper Belt, Plutinos in the 3:2 and Twotinos in the 2:1, contain some of the best-characterized minor objects in the solar system, given their dynamical importance. In particular, Twotinos may hide evidence of Neptune’s early migration. However, these populations vary in time, declining at a rate that has not previously been clearly established. In this work, we use numerical simulations to study the long-term evolution of the Plutino and Twotino populations. We use two data sources: the most up-to-date observations and the theoretical debiased model of the Kuiper Belt known as L7. In addition to studying the giant planets’ effect on these populations over 4 Gyr, we analyze the additional impact produced by the ten most massive trans-Neptunian objects (TNOs) trapped in these resonances, as well as the effect of Pluto on the 2:1 population. We find that the decay rate in each resonance can be modeled as a stochastic process well described by an exponential decay with an offset determined by an underlying long-term stable population. The most massive TNOs, particularly Pluto, influence this decay rate significantly, as expected for the 3:2 resonance. Remarkably, Pluto also strongly influences the 2:1 resonance’s evolution.