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Malena Rice

Publications and source records attributed to Malena Rice.

At least 37 records · Page 2Linked to original sources

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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A High-Precision, Differentiable Code for Solar System Ephemerides

We present jorbit, a python/JAX library designed to enable modern data-driven numerical studies of the solar system. Written entirely in JAX, an auto-differentiable and optionally GPU accelerated language behind many current large-scale machine learning efforts, jorbit includes an independent implementation of REBOUND's IAS15 integrator and the ability to parse precomputed ephemerides such as the JPL DE series. In its default behavior, jorbit maintains ~1 mas agreement with JPL Horizons on ~decade timescales for typical main-belt asteroids, enabling it to fully capitalize on high-precision astrometry and ranging data. We include details of the code's implementation and several worked examples, including illustrations of jorbit's ability to simulate N-body systems, forward model astrometric data, fit orbits, replicate the Minor Planet Center's "MPChecker" service, and contribute to modeling the effect of minor planets on stellar light curves.

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Do White Dwarfs Sample Water-Rich Planetary Material?

Polluted white dwarfs offer a unique way to directly probe the compositions of exoplanetary bodies. We examine the water content of accreted material using the oxygen abundances of 51 highly polluted white dwarfs. Within this sample, we present new abundances for three H-dominated atmosphere white dwarfs that showed promise for accreting water-rich material. Throughout, we explore the impact of the observed phase and lifetime of accretion disks on the inferred elemental abundances of the parent bodies that pollute each white dwarf. Our results indicate that white dwarfs sample a range of dry to water-rich material, with median uncertainties in water mass fractions of $\approx$15\%. Amongst the He-dominated white dwarfs, 35/39 water abundances are consistent with corresponding H abundances. While for any individual white dwarf it may be ambiguous as to whether or not water is present in the accreted parent body, when considered as a population the prevalence of water-rich bodies is statistically robust. The population as a whole has a median water mass fraction of $\approx$25\%, and enforcing chondritic parent body compositions, we find that 31/51 WDs are likely to have non-zero water concentrations. This conclusion is different from a similar previous analysis of white dwarf pollution and we discuss reasons why this might be the case. Pollution in H-dominated white dwarfs continues to be more water-poor than in their He-dominated cousins, although the sample size of H-dominated white dwarfs remains small and the two samples still suffer a disjunction in the range of host star temperatures being probed.

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Requirements for Joint Orbital Characterization of Cold Giants and Habitable Worlds with Habitable Worlds Observatory

We determine optimal requirements for the joint detection of habitable-zone planets and cold giant planets with the Habitable Worlds Observatory (HWO). Analysis of 164 nearby stars shows that a coronagraph outer working angle (OWA) of 1440 milliarcseconds (mas) is necessary to achieve 80-90% visibility of cold giants. Approximately 40 precursor radial velocity measurements with 1 m/s precision are required to adequately constrain orbital parameters before HWO observations. We demonstrate that 6-8 astrometric measurements distributed across the mission timeline, compared to radial velocity constraints alone and to astrometry constraints alone, significantly improve orbital parameter precision, enabling direct determination of orbital inclination with uncertainties of 0.8-3 degrees. For habitable-zone planet characterization, 4-5 epochs provide moderate confidence, while high-confidence (95%) confirmation requires 8+ observations. These specifications are essential for the comprehensive characterization of planetary system architectures and understanding the potential habitability of terrestrial exoplanets.

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A Statistical Method for Constraining the Capability of the Habitable Worlds Observatory to Understand Ozone Onset Time in Earth Analogs

The oxygenation of Earth's atmosphere 2.3 billion years ago, which on exoplanets is expected to be most detectable via the UV ozone feature at $\sim$0.25 $μ$m, is often regarded as a sign of the emergence of photosynthetic life. On exoplanets, we may similarly expect life to oxygenate the atmosphere, but with a characteristic distribution of emergence times. In this paper, we test our ability to recover various "true" emergence time distributions as a function of 1) stellar age uncertainty and 2) number of Earth analogs in the sample. The absolute uncertainties that we recover, for diverse underlying distributions, are mostly independent of the true underlying distribution parameters, and are more dependent on sample size than stellar age uncertainty. For a sample size of 30 Earth analogs, and an HWO architecture sensitive to ozone at 1% of the current atmospheric level on Earth, we find that no ozone detections across the entire sample would place a 10$σ$ limit on the mean time of ozone emergence, regardless of stellar age uncertainty.

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The Formation of Double Hot Jupiter Systems through von Zeipel-Lidov-Kozai Migration

The von Zeipel-Lidov-Kozai (ZLK) mechanism with tidal friction has been demonstrated as a promising avenue to generate hot Jupiters in stellar binary systems. Previous population studies of hot Jupiter formation have largely examined this mechanism in systems comprised of three bodies: two stars and one planet. However, because stars in a binary system form in similar environments with comparable metallicities, the formation of a single hot Jupiter in such a system may imply that the conditions are more likely met for the companion star, as well. We investigate the ZLK mechanism with tidal friction as a potential mechanism to produce double hot Jupiter systems in stellar binaries. Using N-body simulations, we characterize the evolution of two cold Jupiters, each orbiting one star in a binary system, undergoing mirrored ZLK migration. We then examine the robustness of this mechanism to asymmetries in stellar masses, planet masses, and planet orbital inclinations relative to the binary plane. We predict that, under the assumptions that (1) most hot Jupiters in binary star systems form through ZLK migration of primordially formed cold Jupiters and (2) if one star in a binary system forms a cold Jupiter, the second does as well, a comprehensive search could identify double hot Jupiters in up to ~9% of the close- to moderate- separation $a<2000$ AU) binary systems that already host a known hot Jupiter. We also argue that a blind search for ZLK-migrated double hot Jupiters should prioritize twin stellar binaries with pericenter approaches of a few hundred AU.

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JWST Coronagraphic Images of 14 Her c: a Cold Giant Planet in a Dynamically Hot, Multi-planet System

Most observed multi-planet systems are coplanar, in a dynamically "cold" configuration of concentric orbits like our own Solar System. With the James Webb Space Telescope (JWST) we have detected 14 Her c, the first mature and cold exoplanet directly imaged in a dynamically "hot", multi-planet system. With large eccentricities and a nonzero mutual inclination, the present-day architecture of this system points to a turbulent past and ongoing angular momentum exchange between the planetary orbits of 14 Her b and c. The temperature of 14 Her c rivals both the coldest imaged exoplanet and the coldest known brown dwarf. Moreover, its photometry at 4.4 mu is consistent with the presence of carbon disequilibrium chemistry and water ice clouds in its atmosphere. 14 Her c presents a unique laboratory to study giant planet formation, dynamical evolution of multi-planet system architectures, and atmospheric composition and dynamics in extremely cold worlds.

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Peekaboo: Secular Resonances from Evolving Stellar Oblateness Impede Transit Detection

Secular resonances in exoplanet systems occur when two or more planets have commensurabilities in the precession rates of their orbital elements, causing an exchange of angular momentum between them. The stellar gravitational quadrupole moment, which evolves over time due to stellar spin-down over the first $\sim 100\,$Myr, causes these resonances to sweep through the parameter space (of masses and semimajor-axis ratios), affecting a wider variety of systems than when spin-down is neglected. The angular momentum exchange in these resonances typically aligns the outer planets' orbits together while misaligning the innermost planet from its companions. Here, we explore how resonance-induced (mis-)alignments between planets affect the transit outcome. We use the three-planet Kepler-619 system as a concrete case study that is relatively likely (approximately $1$:$1$ odds) to have undergone a sweeping resonance. Consequently, if the outer planets are initially misaligned, a sweeping-resonance-induced push toward alignment in the outer planets' orbits substantially increases the probability that they are observed transiting together. However, the resulting misalignment of the innermost planet from its outer companions, reduces the overall probability that Kepler-619 is observed as a multi-planet transiting system when considering any pair of planets or all three together. This implies that sweeping resonances (which may occur in $20\%$ of systems) have a deleterious effect on the transiting exoplanet sample, suppressing the detection of multi-planet transiting systems in favor of apparent single-planet systems.

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Collisional Fragmentation Support in TRACE

We present improved collision support for TRACE, a state-of-the-art hybrid integrator in REBOUND. TRACE now supports collisional fragmentation and can handle both removing and adding particles mid-timestep. We describe the back-end logic implemented for robust collision support, and compare TRACE's performance to other integrators including MERCURIUS on a large-N protoplanetary disk simulation with various collision prescriptions, a system which TRACE previously could not handle. TRACE matches the behavior of these integrators, while offering potentially vast speedups of over 70x. All updates described in this Note are available with the most recent public release of REBOUND.

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The Case for Edge-On Binaries: An Avenue Toward Comparative Exoplanet Demographics

Most Sun-like and higher-mass stars reside in systems that include one or more gravitationally bound stellar companions. These systems offer an important probe of planet formation in the most common stellar systems, while also providing key insights into how gravitational perturbations and irradiation differences from a companion star alter the outcomes of planet formation. Recent dynamical clues have begun to emerge that reveal systematic, non-random structure in the configurations of many planet-hosting binary systems: in close- to moderate-separation ($s < 800$ au) binary star systems, the orbits of exoplanets around individual stellar components are preferentially aligned with the orbital plane of their host stellar binary. In this work, we flip this narrative and search for nearby, edge-on binary star systems that, due to this preferential alignment, are top candidates for radial velocity and transiting exoplanet searches. We present a sample of 591 moderate-separation, relatively bright ($G < 14$) Gaia-resolved binary star systems in likely near-edge-on configurations. Using a simulated population of exoplanets drawn from transit survey occurrence rate constraints, we provide an overview of the expected planet yields from a targeted search in these systems. We describe the opportunities for comparative exoplanet demographics in the case that both stars can be inferred to host edge-on planetary systems - a configuration toward which the presented sample may be biased, given recent observations of orbit-orbit alignment in exoplanet-hosting binary systems.

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Evidence for Primordial Alignment II: Insights from Stellar Obliquity Measurements for Hot Jupiters in Compact Multiplanet Systems

A significant fraction of hot Jupiters have orbital axes misaligned with their host stars' spin axes. The large stellar obliquities of these giants have long been considered potential signatures of high-eccentricity migration, which is expected to clear out any nearby planetary companions. This scenario requires that only isolated hot Jupiters be spin-orbit misaligned while those with nearby companions, which must have more quiescent histories, maintain low-obliquity orbits, assuming they formed aligned within their primordial protoplanetary disks. Investigations of this stellar obliquity-companionship connection, however, have been severely limited by the lack of hot Jupiters found in compact multi-planet systems. Here we present the sky-projected stellar obliquity ($λ$) of a hot Jupiter with a nearby inner companion recently discovered by NASA's Transiting Exoplanet Survey Satellite: TOI-5143 c. Specifically, we utilize the Doppler shadow caused by the planet's transit, enabled by the Rossiter-McLaughlin (RM) effect, to find that the planet is aligned with $λ=2.1 ^{+2.8}_{-2.7} \circ$. Of the exoplanets with RM measurements, TOI-5143 c becomes just the third hot Jupiter with a nearby companion, and is part of the 19th compact multi-planet single-star system, with an RM measurement. The spin-orbit alignment of these 19 systems provides strong support for primordial alignment, and thus implies that large obliquities are gained primarily due to post-disk dynamical interactions such as those inherent to high-eccentricity migration. As such, the observed spin-orbit alignment of hot Jupiters with nearby companions affirms that some fraction of these giants instead have quiescent origins.

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Planet Masses, Radii, and Orbits from NASA's K2 Mission

We report the masses, sizes, and orbital properties of 86 planets orbiting 55 stars observed by NASA's K2 Mission with follow-up Doppler measurements by the HIRES spectrometer at the W. M. Keck Observatory and the Automated Planet Finder at Lick Observatory. Eighty-one of the planets were discovered from their transits in the K2 photometry, while five were found based on subsequent Doppler measurements of transiting planet host stars. The sizes of the transiting planets range from Earth-size to larger than Jupiter (1-3 REarth is typical), while the orbital periods range from less than a day to a few months. For 32 of the planets, the Doppler signal was detected with significance greater than 5-sigma (51 were detected with >3-sigma significance). An important characteristic of this catalog is the use of uniform analysis procedures to determine stellar and planetary properties. This includes the transit search and fitting procedures applied to the K2 photometry, the Doppler fitting techniques applied to the radial velocities, and the spectral modeling to determine bulk stellar parameters. Such a uniform treatment will make the catalog useful for statistical studies of the masses, densities, and system architectures of exoplanetary systems. This work also serves as a data release for all previously unpublished RVs and associated stellar activity indicators obtained by our team for these systems, along with derived stellar and planet parameters.

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From Misaligned Sub-Saturns to Aligned Brown Dwarfs: The Highest $M_{\rm p}/M{_*}$ Systems Exhibit Low Obliquities, Even around Hot Stars

We present a pattern emerging from stellar obliquity measurements in single-star systems: planets with high planet-to-star mass ratios ($M_{\rm p}/M{_*}$$>$ $2\times10^{-3}$) -- such as super-Jupiters, brown dwarf companions, and M-dwarfs hosting Jupiter-like planets -- tend to be aligned, even around hot stars. This alignment represents a 3.7$σ$ deviation from the obliquity distribution observed in systems with lower mass ratios ($M_{\rm p}/M{_*}$$<$ $2\times10^{-3}$), which predominantly include Jupiters and sub-Saturns. The only known outlier system, XO-3, exhibits misalignment confirmed via our newly collected Rossiter-McLaughlin effect measurement ($λ=41.8^{+2.1}_{-2.0}$ degrees). However, the relatively large $\textit{Gaia}$ Renormalized Unit Weight Error (RUWE) of XO-3 suggests that it may harbor an undetected binary companion, potentially contributing to its misalignment. Given that tidal realignment mechanisms are weak for hot stars, the observed alignment in high $M_{\rm p}/M{_*}$ systems is likely $\textit{primordial}$ rather than resulting from tidal interactions. One possible explanation is that only dynamically isolated planets can continue accreting gas and evolve into super-Jupiters while maintaining their primordial alignment. Conversely, planets formed in compact configurations may be unable to grow beyond the gap-opening mass, for which our work suggests an empirical boundary $M_{\rm p}/M{_*}$$=$ $2\times10^{-3}$, identified between aligned high $M_{\rm p}/M{_*}$ systems and misaligned low $M_{\rm p}/M{_*}$ systems, with dynamical instabilities contributing to the diverse spin-orbit misalignments observed in the latter.

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Planet-Planet Scattering and ZLK Migration -- The Dynamical History of HAT-P-11

The two planets of the HAT-P-11 system represent fascinating dynamical puzzles due to their significant eccentricities and orbital misalignments. In particular, HAT-P-11 b is on a close-in orbit that tides should have circularized well within the age of the system. Here we propose a two-step dynamical process that can reproduce all intriguing aspects of the system. We first invoke planet-planet scattering to generate significant eccentricities and mutual inclinations between the planets. We then propose that this misalignment initiated von-Zeipel-Lidov-Kozai cycles and high-eccentricity migration that ultimately brought HAT-P-11 b to its present-day orbit. We find that this scenario is fully consistent only when significant tidally-driven radius inflation is accounted for during the tidal migration. We present a suite of N-body simulations exploring each phase of evolution and show that this scenario is consistent with all observational posteriors and the reported age of the system.

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Three Warm Jupiters orbiting TOI-6628, TOI-3837, TOI-5027 and one sub-Saturn orbiting TOI-2328

We report the discovery and characterization of three new transiting giant planets orbiting TOI-6628, TOI-3837 and TOI-5027, and one new warm sub-Saturn orbiting TOI-2328, whose transits events were detected in the lightcurves of the Transiting Exoplanet Survey Satellite \textbf{(TESS)} space mission. By combining TESS lightcurves with ground-based photometric and spectroscopic follow-up observations we confirm the planetary nature of the observed transits and radial velocity variations. TOI-6628~$b$ has a mass of 0.75$\pm$0.06~$M_\mathrm{J}$, a radius of 0.98$\pm$0.05~$R_J$ and is orbiting a metal-rich star with a period of 18.18424$\pm{0.00001}$ days and an eccentricity of 0.667$\pm0.016$, making it one of the most eccentric orbits of all known warm giants. TOI-3837~$b$ has a mass of 0.59$\pm$0.06~$M_\mathrm{J}$, a radius of 0.96$\pm$0.05~$R_J$ and orbits its host star every 11.88865$\pm$0.00003~days, with a moderate eccentricity of 0.198$^{+0.046}_{-0.058}$. With a mass of 2.01$\pm$0.13~$M_\mathrm{J}$ and a radius of 0.99$^{+0.07}_{-0.12}$ $R_J$, TOI-5027~$b$ orbits its host star in an eccentric orbit with $e$~=~0.395$^{+0.032}_{-0.029}$ every 10.24368$\pm{0.00001}$~days. TOI-2328~$b$ is a Saturn-like planet with a mass of 0.16$\pm$0.02~$M_\mathrm{J}$ and a radius of 0.89$\pm$0.04~$R_J$, orbiting its host star in a nearly circular orbit with $e$~=~0.057$^{+0.046}_{-0.029}$ at an orbital period of 17.10197$\pm{0.00001}$ days. All four planets have orbital periods above 10 days, and our planet interior structure models are consistsent a rocky-icy core with a H/He envelope, providing evidence supporting the core accretion model of planet formation for this kind of planets.

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More Likely Than You Think: Inclination-Driving Secular Resonances are Common in Known Exoplanet Systems

Multi-planet systems face significant challenges to detection. For example, further orbiting planets have reduced signal-to-noise ratio in radial velocity detection methods, and small mutual inclinations between planets can prevent them from all transiting. One mechanism to excite mutual inclination between planets is secular resonance, where the nodal precession frequencies of the planets align such as to greatly increase the efficiency of angular momentum transport between planets. These resonances can significantly misalign planets from one another, hindering detection, and typically can only occur when there are three or more planets in the system. Naively, systems can only be in resonance for particular combinations of planet semimajor axes and masses; however, effects that alter the nodal precession frequencies of the planets, such as the decay of stellar oblateness, can significantly expand the region of parameter space where resonances occur. In this work, we explore known three-planet systems, determine whether they are in (or were in) secular resonance due to evolving stellar oblateness, and demonstrate the implications of resonance on their detectability and stability. We show that about 20% of a sample of three planet transiting systems seem to undergo these resonances early in their lives.

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HD 222237 b: a long period super-Jupiter around a nearby star revealed by radial-velocity and Hipparcos-Gaia astrometry

Giant planets on long period orbits around the nearest stars are among the easiest to directly image. Unfortunately these planets are difficult to fully constrain by indirect methods, e.g., transit and radial velocity (RV). In this study, we present the discovery of a super-Jupiter, HD 222237 b, orbiting a star located $11.445\pm0.002$ pc away. By combining RV data, Hipparcos and multi-epoch Gaia astrometry, we estimate the planetary mass to be ${5.19}_{-0.58}^{+0.58}\,M_{\rm Jup}$, with an eccentricity of ${0.56}_{-0.03}^{+0.03}$ and a period of ${40.8}_{-4.5}^{+5.8}$ yr, making HD 222237 b a promising target for imaging using the Mid-Infrared Instrument (MIRI) of JWST. A comparative analysis suggests that our method can break the inclination degeneracy and thus differentiate between prograde and retrograde orbits of a companion. We further find that the inferred contrast ratio between the planet and the host star in the F1550C filter ($15.50\,μ\rm m$) is approximately $1.9\times10^{-4}$, which is comparable with the measured limit of the MIRI coronagraphs. The relatively low metallicity of the host star ($\rm-0.32\,dex$) combined with the unique orbital architecture of this system presents an excellent opportunity to probe the planet-metallicity correlation and the formation scenarios of giant planets.

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squishyplanet: Modeling Transits of Non-spherical Exoplanets in JAX

While astronomers often assume that exoplanets are perfect spheres when analyzing observations, the subset of these distant worlds that are subject to strong tidal forces and/or rapid rotations are expected to be distinctly ellipsoidal or even triaxial. Since a planet's response to these forces is determined in part by its interior structure, measurements of an exoplanet's deviations from spherical symmetry can lead to powerful insights into its composition and surrounding environment. These shape deformations will imprint themselves on a planet's phase curve and transit lightcurve and cause small (1s-100s of parts per million) deviations from their spherical-planet counterparts. Until recently, these deviations were undetectable in typical real-world datasets due to limitations in photometric precision. Now, however, current and soon-to-come-online facilities such as JWST will routinely deliver observations that warrant the consideration of more complex models. To this end we present squishyplanet, a JAX-based Python package that implements an extension of the polynomial limb-darkened transit model presented in Agol et al. 2020 to non-spherical (triaxial) planets, as well as routines for modeling reflection and emission phase curves.

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