arXiv subjects

Cristobal Petrovich

Publications and source records attributed to Cristobal Petrovich.

At least 19 recordsLinked to original sources

arXiv2026

POSEIDON III: The Aligned Orbit of the Hot Neptune Around the Hot Star WASP-195

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 effect in the hot-star/hot-Neptune system WASP-195 ($T_{\rm eff}=6470\pm100$ K, $v\sin{i_\star}=10.5\pm1.1$ 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 $λ=-10\pm7^\circ$, 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 $5σ$ 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 Rossiter-McLaughlin effect, a feature that could help to widen the planet confirmation bottleneck while expanding the obliquity census of small planets around hot stars.

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arXiv2026

Planet-Planet Secular Migration Predicts a Stellar Obliquity-Period Anti-Correlation

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.

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arXiv2026

High-Eccentricity Tidal Migration Driven by Secular Chaos in Wide-Binary Systems

High-eccentricity tidal migration driven by a distant stellar companion offers a natural pathway for producing some hot Jupiters; yet, most theoretical work has relied on an idealized three-body configuration whose simplicity makes the problem especially tractable. In reality, many cold-Jupiter systems may host additional planets or substellar objects, whose interactions can dramatically alter the pathways to secularly excite extreme eccentricities. We investigate how secular chaos can drive high-eccentricity tidal migration in hierarchical ``3+1'' systems--stellar binaries hosting a planet and an additional intermediate companion orbiting the primary star. We show that the onset of secular chaos is regulated by the ratio of the von-Zeipel-Lidov-Kozai (ZLK) timescales of the inner and outer orbits $\mathcal{R}$. When $\mathcal{R}\sim 0.5-2$, most systems can undergo migration even when their mutual inclinations remain modest--below the $39.2^\circ$ critical angle for ZLK oscillations--with diffusion timescales spanning a broad range, up to thousands of inner orbit ZLK timescales. For larger mutual inclinations, secular migration operates over a much broader region of parameter space with $\mathcal{R} \sim 0.05-100$, but most evolutionary pathways become non-secular and potentially unstable--behavior recently identified as an alternative pathway to tidal migration. Our model predicts hot Jupiters in nearly polar orbits relative to both the host star's stellar equator (stellar obliquities $\sim 60^\circ-120^\circ$) and the orbits of the outer two companions. Future Gaia releases and long-term radial velocity campaigns are likely to uncover additional ``3+1'' systems, providing valuable opportunities to test this migration pathway.

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arXiv2026

Thermally Regulated Viscoelastic Tidal Migration of Eccentric 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.

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arXiv2026

POSEIDON II: The Anti-Aligned Orbit of the Warm Neptune TOI-1710 A b

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 ($P\sim24$ days), and our observations reveal that it orbits in the opposite direction to the stellar spin, with a sky-projected obliquity $λ=179\pm19^{\circ}$. Combined with information about the rotation period of the host star, we measure a true obliquity $ψ=158_{-13}^{+11}\,^{\circ}$. The host star has an M-dwarf companion at a separation of $\sim3600$ 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 $\sim5\,M_J$ planet on a $\sim15$ au orbit that is nearly aligned with the transiting planet's orbit.

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arXiv2026

POSEIDON I: The Dynamical Origins of Transiting Neptunes

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/PFS and WIYN/NEID. TOI-181 b is on a 4.5-day orbit with a sky-projected spin-orbit misalignment $λ= 32.0_{-6.5}^{+6.3}\,^{\circ}$ and a low eccentricity ($e<0.12$ with $2σ$ confidence). TOI-883 b has a longer orbital period of 10 days with $λ= 22_{-14}^{+15}\,^{\circ}$ and eccentricity $e = 0.16 \pm 0.03$. 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.

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arXiv2026

Planetesimal-Driven Instabilities in Resonant Chains of Cold Neptunes and Their Dynamical Outcomes

Cold Neptunes and sub-Neptunes are among the most common products of planet formation and likely dominate the angular-momentum budgets in most planetary systems, yet their dynamical impact on planetary architectures remains poorly understood. Using N-body simulations, we investigate the evolution of multi-Neptune systems assembled into resonant chains during the gas-disk phase and later coupled to remnant planetesimal disks. We show that planetesimal disks containing $\simeq 1$-$4\%$ of the planetary mass efficiently disrupt resonant chains and trigger global dynamical instabilities on timescales of $1~\mathrm{Myr}$-$1~\mathrm{Gyr}$, providing a pathway for delayed instability long after gas-disk dispersal, albeit with instability timescales that are highly sensitive to disk mass. The ensuing instability drives large-scale orbital rearrangement and loss of planets through collisions, tidal disruption, and ejections. Notably, in most systems at least one planet is scattered inward to $\sim 0.1~\mathrm{au}$ on $\sim 10$-$100$ Myr timescales (for $\sim 5$-$50\; M_\oplus$ planets) following instability onset, with a substantial fraction undergoing tidal capture or disruption. This tidal capture can provide a natural pathway to hot Neptune formation, while compact inner chains, if present, would be destroyed on $\sim 100~\mathrm{Myr}$ timescales by cold sub-Neptunes, naturally explaining the observed decline in the resonant fraction. We argue that the predictions of our model, which yields mass-segregated planets and corresponding relative abundances of cold, wide-orbit, and free-floating planets, can be tested by ongoing and upcoming microlensing surveys.

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arXiv2026

The Effect of Massive Trans-Neptunian Objects in the Long-term Evolution and Leaking Rates of Neptune's 3:2 and 2:1 Mean Motion Resonances

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 been previously 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.

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arXiv2025

A Cold and Super-Puffy Planet on a Prograde Orbit

We report the discovery of TOI-4507 b, a transiting sub-Saturn with a density $<$ 0.2 g/cm$^3$ on a 105-day prograde orbit around a 700 Myr old F star. The transits were detected using data from TESS as well as the Antarctic telescope ASTEP. A joint analysis of the light curves and radial velocities from HARPS, FEROS, and CORALIE confirmed the planetary nature of the signal by limiting the mass to be below 20 $M_\oplus$ at 95% confidence. The radial velocities also exhibit the Rossiter-McLaughlin effect and imply that the planet orbits the star in a prograde orbit with a sky-projected obliquity $λ=-15_{-44}^{+50}$ deg ($|λ|<80$ deg at $3σ$). With these characteristics, TOI-4507 is one of the longest-period systems for which the stellar obliquity has been measured, and the planet is among the longest-period and youngest ''super-puff'' planets yet discovered.

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arXiv2025

Early Evidence for Polar Orbits of Sub-Saturns Around Hot Stars

Sub-Saturns have been reported to preferentially occupy near-polar orbits, but this conclusion has so far been based primarily on systems with cool host stars; obliquity measurements for sub-Saturns orbiting hot stars remain scarce. Expanding the census into the hot-star regime is essential to test whether the polar preference persists across the Kraft break and to diagnose the underlying excitation mechanisms. In this work, we present Rossiter-McLaughlin observations of TOI-1135 b, a sub-Saturn orbiting a hot star with $T_{\rm eff}=6320\pm120$ K, using WIYN/NEID. We confirm its near-polar architecture, measuring a sky-projected obliquity of $λ=-68.1^{+7.5}_{-5.3}$ degrees and a true obliquity of $ψ=72.2^{+6.4}_{-6.6}$ degrees. Coupling our new measurement with stellar-obliquity data from the literature, we find that sub-Saturns and hot Jupiters around cool stars are unlikely to be drawn from the same parent distribution at the $5.2σ$ level, consistent with weaker tidal realignment induced by lower-mass planets. Of the two known misaligned sub-Saturns around hot stars, both are near-polar, suggesting that the polar preference may extend above the Kraft break. Moreover, their obliquities lie near $\sim 65$ degrees, supporting predictions from secular resonance crossing for sub-Saturns around rapidly rotating hot stars.

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arXiv2025

The vertical structure of debris discs and the role of disc gravity: A primer using a simplified model

Debris discs provide valuable insights into the formation and evolution of exoplanetary systems. Their structures are commonly attributed to planetary perturbations, serving as probes of as-yet-undetected planets. However, most studies of planet-debris disc interactions ignore the disc's gravity, treating it as a collection of massless planetesimals. Here, using an analytical model, we investigate how the vertical structure of a back-reacting debris disc responds to secular perturbations from an inner, inclined planet. Considering the disc's axisymmetric potential, we identify two dynamical regimes: planet-dominated and disc-dominated, which may coexist, separated by a secular-inclination resonance. In the planet-dominated regime ($M_d/m_p\ll1$), we recover the classical result: a transient warp propagates outward until the disc settles into a box-like structure centered around the planetary orbit's initial inclination $I_p(0)$, with a distance-independent aspect ratio $\mathcal{H}(R)\approx I_p(0)$. In contrast, in the disc-dominated regime ($M_d/m_p\gtrsim1$), the disc exhibits dynamical rigidity, remaining thin and misaligned, with significantly suppressed inclinations and a sharply declining aspect ratio, $\mathcal{H}(R)\propto I_p(0)R^{-7/2}$. In the intermediate regime ($M_d/m_p\lesssim1$), the system exhibits a secular-inclination resonance, leading to long-lived, warp-like structures and a bimodal inclination distribution, containing both dynamically hot and cold populations. We provide analytic formulae describing these effects as a function of system parameters. We also find that the vertical density profile is intrinsically non-Gaussian and recommend fitting observations with non-zero slopes of $\mathcal{H}(R)$. Our results may be used to infer planetary parameters and debris disc masses based on observed warps and scale heights, as demonstrated for HD 110058 and $β$ Pic.

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arXiv2025

The Influence of Cold Jupiters in the Formation of Close-in planets. II. Collisional Growth of Planetesimals

Exoplanet observations have shown that the occurrence and orbital architectures of close-in super-Earths and sub-Neptunes are shaped by the presence of outer gas giant planets. This influence may emerge during the formation stage or from later dynamical evolution by a yet elusive physical process. In this work, we investigate the early stages of planetesimal accretion, modeling the joint collisional and dynamical evolution of planetesimals under the gravitational influence of a cold Jupiter and a viscously-dissipating massive protoplanetary disk. We find that an initially extended planetesimal disk of small ($\sim 1-10$ km) bodies evolves into massive, compact ($Δa/a\lesssim 0.1$) rings of several Earth masses in Moon-sized objects centered at $\sim0.1-0.5$ au. This prevalent outcome is the result of an initial stage of planetesimal accretion over the first 10 kyrs, followed by orbital transport driven by a secular apsidal resonance sweeping inward on Myr timescales. Our findings highlight the crucial role of giant planets in redistributing solids within the inner disk. This redistribution of planetary building blocks may help explain why systems with giant companions often depart from the "peas-in-a-pod" architecture.

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arXiv2025

Destruction of "Peas in a Pod?" A Candidate Multi-planet System Around the Nearby, Bright Star, HD208487

We re-investigate the HD208487 system to test the reality of the proposed HD208487c world. We also search for additional companions using applied Bayesian statistics and 15+ years of new RV data from the HARPS and the PFS instruments that were taken post-discovery of HD208487b. The RV data was analyzed with GLS Periodograms, followed by Bayesian analysis using the EMPEROR code. We scrutinised various stellar activity indices to search for any corresponding peaks in the power spectra, correlations with the RV measurements, or significant signals from a Bayesian analysis methodology. Finally, photometric data was checked to test for any transits or possible activity manifestations that could lead to possible false RV signals or excess noise. Our analysis points towards a candidate second planet in the system, positioned near the period of a previously proposed and subsequently challenged signal. This signal, HD208487c, would relate to a cool Saturn with an orbital period of 923.06 +2.02 -2.76 d and a minimum mass of Mj sini = 0.32 +/- 0.01Mj. Our analysis also gives rise to a newly discovered candidate planet, HD208487d, which would be the result of a cool super-Neptune/sub-Saturn with a period of 1380.13 +19.20 -8.25 d and a minimum mass of Mj sini = 0.15 +/- 0.01Mj. Neither stellar activity indices nor photometric data show signals statistically matching these periods. We have uncovered a candidate three planet system that would consist of an inner gas giant, a central Saturn and an outer super-Neptune/sub-Saturn. A dynamical analysis suggests that gravitational scattering of an initially ordered, equally-spaced system in a long resonant chain of six Neptunes can explain the current proposed architecture of HD208487. More RVs may also shed light on the reality of a fourth Doppler signal uncovered in the data that sits close to the 2:1 period-ratio with signal of HD208487c.

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arXiv2025

TOI-1259Ab: A Warm Jupiter Orbiting a K-dwarf White-Dwarf Binary is on a Well-aligned Orbit

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 AGB stage gives it a "kick" that can initiate Eccentric Lidov-Kozai oscillations, potentially causing a planet around the secondary star to migrate inwards and perturbing 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 $λ= 6^{+21}_{-22}\,^\circ$. When combined with estimates of the stellar rotation period, radius, and projected rotation velocity, we find the true 3D obliquity to be $ψ= 24^{+14}_{-12}\,^\circ$ ($ψ< 48^\circ$ at 95% confidence), revealing that the orbit of TOI-1259Ab is well aligned with 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 well-aligned configuration. Alternatively, as we show with dynamical simulations, Eccentric Lidov-Kozai oscillations triggered by the evolution of the binary companion are expected to lead to a low obliquity with a probability of about $\sim$14%.

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arXiv2025

The Spin-Orbit Alignment of 8 Warm Gas Giant Systems

Essential information about the formation and evolution of planetary systems can be found in their architectures -- in particular, in stellar obliquity ($ψ$) -- as they serve as a signature of their dynamical evolution. Here, we present ESPRESSO observations of the Rossiter-Mclaughlin (RM) effect of 8 warm gas giants, revealing that independent of the eccentricities, all of them have relatively aligned orbits. Our 5 warm Jupiters -- WASP-106 b, WASP-130 b, TOI-558 b, TOI-4515 b, and TOI-5027 b -- have sky-projected obliquities $|λ|\simeq0-10$ deg while the 2 less massive warm Saturns -- K2-139 b and K2-329 A b -- are slightly misaligned having $|λ|\simeq15-25$ deg. Furthermore, for K2-139 b, K2-329 A b, and TOI-4515 b, we also measure true 3D obliquities $ψ\simeq15-30$ deg. We also report a non-detection of the RM effect produced by TOI-2179 b. Through hierarchical Bayesian modeling of the true 3D obliquities of hot and warm Jupiters, we find that around single stars, warm Jupiters are statistically more aligned than hot Jupiters. Independent of eccentricities, 95\% of the warm Jupiters have $ψ\lesssim30$ deg with no misaligned planets, while hot Jupiters show an almost isotropic distribution of misaligned systems. This implies that around single stars, warm Jupiters form in primordially aligned protoplanetary disks and subsequently evolve in a more quiescent way than hot Jupiters. Finally, we find that Saturns may have slightly more misaligned orbits than warm Jupiters, but more obliquity measurements are necessary to be conclusive.

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arXiv2025

Origin of the asymmetric gas distribution near the co-orbital Lagrange points of an embedded planet

Hydrodynamic simulations of planet-disk interactions often show material accumulation near the co-orbital Lagrange points $L_4$ and $L_5$ -- features that may correspond to observed crescents in protoplanetary disks. Intriguingly, these simulations also show an asymmetrical distribution of gas between $L_4$ and $L_5$, whose physical origin is not yet understood and could allow to further constrain the inner workings of planet-disk interactions. We performed 2D hydrodynamic simulations of a single, non-migrating planet embedded in a gaseous disk to investigate this effect. We find that the asymmetry is solely controlled by the sign of the radial temperature gradient with positive gradients enhancing the accumulation at $L_4$ and negative ones enhancing $L_5$. A symmetric distribution is recovered on globally isothermal disks. Furthermore, we find that the azimuthal locations of $L_4$ and $L_5$ deviate from the classical circular restricted three-body problem, following a monotonic trend with the disk pressure scale height $h_{\rm p}$: $ϕ_{\text{max}}\approx\pm60^{\circ}[1+0.18(h_{\rm p}^3M_\star/m_{\rm p})^{2/3}]$. Our simulations show that the longest-lived and largest-amplitude structures are produced by planets opening gaps with depths $Σ_{\rm gap}/Σ_0\lesssim 0.2$. We successfully reproduce the observed asymmetry using a semi-analytical model that incorporates the azimuthally asymmetric radial velocity background induced by the planet. Overall, our results suggest that asymmetries in the form of crescents and clumps inside of density gaps opened by planets can constrain the local thermodynamic properties of protoplanetary disks.

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arXiv2025

The chaotic history of the retrograde multi-planet system in K2-290A driven by distant stars

The equator of star K2-290A was recently found to be inclined by 124+/-6 degrees relative to the orbits of both its known transiting planets. The presence of a companion star B at ~100 au suggested that the birth protoplanetary disk could have tilted, thus providing an explanation for the peculiar retrograde state of this multi-planet system. In this work, we show that a primordial misalignment is not required and that the observed retrograde state is a natural consequence of the chaotic stellar obliquity evolution driven by a wider-orbit companion C at ~2000 au long after the disk disperses. The star C drives eccentricity and/or inclination oscillations on the inner binary orbit, leading to widespread chaos from the periodic resonance passages between the stellar spin and planetary secular modes. Based on a population synthesis study, we find that the observed stellar obliquity is reached in ~40-70% of the systems, making this mechanism a robust outcome of the secular dynamics,regardless of the spin-down history of the central star. This work highlights the unusual role that very distant companions can have on the orbits of close-in planets and the host star's spin evolution, connecting four orders of magnitude in distance scale over billions of orbits. We finally comment on the application to other exoplanet systems, including multi-planet systems in wide binaries.

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arXiv2024

Evidence for Primordial Alignment: Insights from Stellar Obliquity Measurements for Compact Sub-Saturn Systems

Despite decades of effort, the mechanisms by which the spin axis of a star and the orbital axes of its planets become misaligned remain elusive. Particularly, it is of great interest whether the large spin-orbit misalignments observed are driven primarily by high-eccentricity migration -- expected to have occurred for short-period, isolated planets -- or reflect a more universal process that operates across systems with a variety of present-day architectures. Compact multi-planet systems offer a unique opportunity to differentiate between these competing hypotheses, as their tightly-packed configurations preclude violent dynamical histories, including high-eccentricity migration, allowing them to trace the primordial disk plane. In this context, we report measurements of the sky-projected stellar obliquity ($λ$) via the Rossiter-McLaughlin effect for two sub-Saturns in multiple-transiting systems: TOI-5126 b ($λ=1\pm 48 ^\circ$) and TOI-5398 b ($λ=-8.1^{+5.3 \circ}_{-6.3}$). Both are spin-orbit aligned, joining a fast-growing group of just three other compact sub-Saturn systems, all of which exhibit spin-orbit alignment. In aggregate with archival data, our results strongly suggest that sub-Saturn systems are primordially aligned and become misaligned largely in the post-disk phase, as appears to be the case increasingly for other exoplanet populations.

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