arXiv subjects

Juliette Becker

Publications and source records attributed to Juliette Becker.

At least 37 records · Page 2Linked to original sources

arXiv2025

Mean Motion Resonances in AGN Disks

Mean motion resonances (MMRs) are a generic outcome of convergent migration for bodies embedded in accretion disks around a central mass. Long studied in planetary systems, the same phenomenon should occur for stellar-mass black holes (BHs) in AGN disks. In this work, we derive simple analytic criteria describing when BH pairs are driven out of resonance, and use them to chart MMR stability across AGN parameter space, accounting for disruption from general-relativistic apsidal precession, hydrodynamic turbulence, and stellar stirring. Across plausible AGN disk models, we find three MBH mass regimes: (i) for $M/ M_\odot\gtrsim 10^{7.5}$, first order resonances are generically unstable; (ii) for $M/ M_\odot\lesssim 10^{6.5}$, stable MMRs are always present; (iii) for $10^{6.5}\lesssim M / M_\odot \lesssim 10^{7.5}$, stability depends on disk mass flux, the summed mass of the orbiters, and the nuclear-cusp slope. When present, stable MMRs commonly occur between an inner anti-trap and an outer trap set by thermal torque, a region where embedded objects migrate outward in the disk. These results imply that high-mass AGN allow convergent migration to proceed to LVK-band mergers largely without resonant chains, whereas low/intermediate-mass AGN can host MMRs, with the potential to reshape merger pathways.

astro-ph.HE↗

arXiv2025

General Relativity Can Prevent a Runaway Greenhouse on Potentially Habitable Planets Orbiting White Dwarfs

Planets orbiting in the habitable zones of white dwarfs have recently been proposed as promising targets for biosignature searches. However, since the white dwarf habitable zone resides at 0.01 - 0.1 AU, planets residing there are subject to tidal heating if they have any orbital eccentricity. Previous work (Barnes & Heller 2013) identified nearby planetary companions as potential roadblocks to habitability of planets around white dwarfs, as such companions could induce secular oscillations in eccentricity for the potentially habitable planet, which could in turn heat a surface ocean and induce a runaway greenhouse for even very low values ($e \sim 10^{-4}$) of the eccentricity of the potentially habitable planet. In this work, we examine the potential for general relativistic orbital precession to protect habitable planets orbiting white dwarfs from such a runaway greenhouse, and demonstrate that for some system architectures, general relativity can be protective for planetary habitability.

astro-ph.EP↗

arXiv2025

THYME XIII: Two young Neptunes orbiting a 75-Myr star in the Alpha Persei Cluster

Young planets with mass measurements are particularly valuable in studying atmospheric mass-loss processes, but these planets are rare and their masses difficult to measure due to stellar activity. We report the discovery of a planetary system around TOI-6109, a young, 75 Myr-old Sun-like star in the Alpha Persei cluster. It hosts at least two transiting Neptune-like planets. Using three TESS sectors, 30 CHEOPS orbits, and photometric follow-up observations from the ground, we confirm the signals of the two planets. TOI-6109 b has an orbital period of P=$5.6904^{+0.0004}_{-0.0004}$ days and a radius of R=$4.87^{+0.16}_{-0.12}$ R$_\oplus$. The outer planet, TOI-6109 c has an orbital period of P=$8.5388^{+0.0006}_{-0.0005}$ days and a radius of R=$4.83^{+0.07}_{-0.06}$ R$_\oplus$. These planets orbit just outside a 3:2 mean motion resonance. The near-resonant configuration presents the opportunity to measure the planet's mass via TTV measurements and to bypass difficult RV measurements. Measuring the masses of the planets in this system will allow us to test theoretical models of atmospheric mass loss.

astro-ph.EP↗

arXiv2025

Why M-dwarf flares have limited impact on the atmospheric evaporation of sub-Neptunes and Earth-sized planets

M-type stars are prime targets for exoplanet searches within their habitable zones (HZs). These stars also exhibit significant magnetic flaring activity, particularly during their first billion years, which can potentially accelerate the evaporation of the hydrogen-helium envelopes of close-in planets. We employ the time-dependent photoionization hydrodynamics code ATES to investigate the impact of flares on atmospheric escape, focusing on an Earth-sized and a sub-Neptune-sized planet orbiting an early M-type star at distances of 0.01, 0.1, and 0.18-0.36 AU-the inner and outer edges of the HZ. Stellar flaring is modeled as a 1 Gyr-long high-activity phase followed by a 4 Gyr-long low-activity phase, each characterized by an appropriate flare frequency distribution. We find that flares have a modest impact-less than a factor of two-on the cumulative atmospheric mass loss, with the greatest absolute enhancement occurring when the planets are at their closest separation. However, the relative enhancement in mass loss between flaring and non-flaring cases is greater at larger orbital separations. This trend arises because, as stellar irradiation fluctuates between quiescent levels and peak flares, the proportion of time that a planet spends in the energy-limited versus recombination-limited mass loss regimes depends on its orbital separation. Additionally, we demonstrate the existence of a characteristic flare energy, intermediate between the minimum and maximum values, that maximizes the fractional contribution to flare-driven mass loss. Our results indicate that the flaring activity of M-dwarfs does not significantly affect the atmospheric retention of close-in planets, including those within the HZ. The potential occurrence of rare super-flares, which current observational campaigns may be biased against, does not alter our conclusions.

astro-ph.EP↗

arXiv2025

An Eccentric Sub-Neptune Moving Into the Evaporation Desert

Though missions such as Kepler, K2, and TESS have discovered $>$2,000 sub-Neptune and Neptunian planets, there is a dearth of such planets at close-in (P$\lesssim$3 days) orbits. This feature, called the Neptune desert or the evaporation desert, is believed to be primarily shaped by planetary migration and photoevaporation. However, this region is not completely devoid of planets--a small number of very hot Neptunes reside within the desert. These planets provide an opportunity to directly probe the effects of migration and photoevaporation. We present confirmation of TOI-5800 b, an eccentric sub-Neptune on a $\approx$2.6 day period that is likely actively undergoing tidal migration. We use radial velocity measurements from the Carnegie Planet Finder Spectrograph (PFS) to constrain TOI-5800 b's mass and eccentricity. We find that it has an unusually high eccentricity (0.39$\pm$0.07) for its short orbit. TOI-5800 is therefore currently experiencing high levels of tidal heating as it moves into the desert. Ranked as a top candidate for transmission and emission spectroscopy within its temperature and radius regime, TOI-5800 b is a prime target for atmospheric characterization with JWST. TOI-5800 b presents a unique opportunity to study the atmosphere of a planet undergoing tidal heating and to probe the composition of sub-Neptune planets.

astro-ph.EP↗

arXiv2025

Tides Tighten the Hycean Habitable Zone

Hycean planets -- exoplanets with substantial water ice layers, deep surface oceans, and hydrogen-rich atmospheres -- are thought to be favorable environments for life. Due to a relative paucity of atmospheric greenhouse gases, hycean planets have been thought to have wider habitable zones than Earth-like planets, extending down to a few times 0.001 au for those orbiting M dwarfs. In this Letter, we reconsider the hycean habitable zone accounting for star-planet tidal interaction. We show that for a moderately eccentric hycean planet, the surface temperature contribution from tidal heating truncates the habitable zone at significantly larger orbital radii, and that moderate eccentricity is readily obtained from any massive outer companion in the system. Though few current hycean planet candidates orbit stars of low enough mass for tides to plausibly significantly alter the extent of the habitable zone, this effect will be important to note as more such candidates are identified orbiting M dwarfs. We suggest that tides are a significant factor both for determining the extent of the hycean habitable zone around low-mass stars and for the development of a detectable hycean biosphere.

astro-ph.EP↗

arXiv2025

Three-Dimensional Orbital Architectures and Detectability of Adjacent Companions to Hot Jupiters

The orbital properties of the (as-yet) small population of hot Jupiters with nearby planetary companions provide valuable constraints on the past migration processes of these systems. In this work, we explore the likelihood that dynamical perturbations could cause nearby inner or outer companions to hot Jupiter to leave the transiting plane, potentially leaving these companions undetected despite their presence at formation. Using a combination of analytical and numerical models, we examine the effects of stellar evolution on hot Jupiter systems with nearby companions and identify several possible outcomes. We find that while inner companions are generally unlikely to leave the transiting plane, outer companions are more prone to decoupling from the hot Jupiter and becoming non-transiting, depending on the system's initial orbital architecture. Additionally, we observe a range of dynamical behaviors, including overall stability, inclination excitation, and, in some cases, instability leading to the ejection or collision of planets. We also show that the effect of stellar obliquity (with respect to the mean planet of the planets) is to amplify these effects and potentially cause outer companions to attain non-mutually-transiting configurations more often. Our results highlight the complex dynamical pathways shaping the architectures of hot Jupiter systems.

astro-ph.EP↗

arXiv2025

Thermal Evolution and Mass Loss on Short-Period, Low-Mass Planets During FU Orionis Outbursts

Ultra-short-period (USP) planets represent a unique class of exoplanets characterized by their tight orbits and relatively low masses, with some also exhibiting unusually high iron fractions. Previous work (Becker et al, 2021) proposed a dynamical pathway wherein planets can migrate inward due to drag from sub-Keplerian gas during episodic FU Orionis (FU Ori) outbursts, an abrupt accretion phenomenon exhibited by young stellar objects, thereby potentially populating USP orbits. However, the implications of this migration process on the structural and compositional evolution of these planets remain unexplored. In this work, we model the response of a planet's surface material to the high disk temperatures characteristic of an FU Ori event and compute the fraction of an Earth-like planet's mass that will be lost due to vaporization and subsequent turbulent diffusion of gaseous molecules during the FU Ori event. We find that low-mass planets may lose a substantial fraction of their mantle mass during FU Ori events, potentially contributing to the observed prevalence of low-mass, iron-rich USP planets.

astro-ph.EP↗

arXiv2025

The Ambiguous Age and Tidal History for the Ultra-Hot Jupiter TOI-1937Ab

Ultra-short-period (USP) planets are a rare but dynamically significant subset of the exoplanet sample, and understanding their dynamical histories and migration processes is necessary to build a complete picture of the outcomes of planet formation. In this work, we present an analysis of system age constraints and the impact of tidal evolution in the TOI-1937A system, a component of a large-separation stellar binary with an ambiguous age constraint that hosts a massive (> 2 $M_{Jup}$) USP planetary companion. Through a suite of tidal evolution simulations and analysis of the transit timing variations present in the photometric data, we find that the ultra-hot Jupiter TOI-1937Ab is likely undergoing orbital decay driven by tidal interactions, and we place an observational upper limit on its decay rate of |$\dot{P}$| < 0.09. We consider three different hypotheses for the system age based on three distinct methods of age estimation. These three age limits are complemented by indirect evidence of the age of the star that comes from our dynamical and transit timing analyses. We discuss the possibility that future data will provide more concrete constraints on the tidal parameters of TOI-1937Ab and its host star.

astro-ph.EP↗

arXiv2025

A long spin period for a sub-Neptune-mass exoplanet

HIP 41378 f is a sub-Neptune exoplanet with an anomalously low density. Its long orbital period and deep transit make it an ideal candidate for detecting oblateness photometrically. We present a new cross-platform, GPU-enabled code greenlantern, suitable for computing transit light curves of oblate planets at arbitrary orientations. We then use Markov Chain Monte Carlo to fit K2 data of HIP 41378 f, specifically examining its transit for possible oblateness and obliquity. We find that the flattening of HIP 41378 f is $f \leq 0.889$ at the 95% confidence level, consistent with a rotation period of $P_\text{rot} \geq 15.3$ hr. In the future, high-precision data from JWST has the potential to tighten such a constraint and can differentiate between spherical and flattened planets.

astro-ph.EP↗

arXiv2025

The Effects of Kinematic MHD on the Atmospheric Circulation of Eccentric Hot Jupiters

Hot Jupiters are typically considered to be tidally locked due to their short orbital periods. The extreme irradiation can result in atmospheric species becoming thermally ionized on the dayside, which then interact with the planet's magnetic field by resisting flow across magnetic field lines, shaping the atmospheric structure. However, an eccentric orbit results in temporally dependent irradiation and a non-permanent dayside, as the planet-star distance can change drastically during its orbit. In this paper, we present 3D atmospheric models of TOI-150b, an eccentric (e=0.26), Jupiter-mass 1.75 M_Jup planet whose equilibrium temperature varies from 1300K to 1700K. We conduct simulations for magnetic field strengths ranging from 0-30 Gauss using the kinematic magnetohydrodynamics (MHD) approach. When compared to simulations of the planet assuming a circular orbit, we find that the eccentric orbit results in a strengthened and narrowed equatorial jet, westward winds at mid-latitudes, and a phase-dependent thermal inversion. The strength and magnitude of these effects scale with the chosen global magnetic field strength. We also generate high-resolution (R=100,000) emission spectra to study net Doppler shifts and find inter-orbit spectroscopic variability at moderate magnetic field strengths, as well as decreased Doppler broadening as magnetic field strengths increase. This work represents the first time that the kinematic MHD approach has been applied to an eccentric hot Jupiter and highlights the importance of a locally calculated, temperature dependent magnetic drag prescription for predicting atmospheric structure and resulting spectra.

astro-ph.EP↗

arXiv2025

A Pair of Dynamically Interacting Sub-Neptunes Around TOI-6054

We confirm the planetary nature of a pair of transiting sub-Neptune exoplanets orbiting the bright F-type sub-giant star TOI-6054 ($V=8.02$, $K=6.673$) as a part of the OrCAS radial velocity survey using WIYN/NEID observations. We find that TOI-6054b and TOI-6054c have radii of $2.65 \pm 0.15$ $R_{\oplus}$ and $2.81 \pm 0.18$ $R_{\oplus}$, respectively, and masses of $12.4 \pm 1.7$ $M_{\oplus}$ and $9.2 \pm 2.0$ $M_{\oplus}$. The planets have zero-albedo equilibrium temperatures of $1360 \pm 33$ K and $1144 \pm 28$ K. The host star has expanded and will evolve off of the Main Sequence within the next $\sim$500 Myr, and the resulting increase in stellar luminosity has more than doubled the stellar flux the two planets receive compared to the start of the host star's main sequence phase. Consequently, TOI-6054b may be losing some of its primordial H/He atmosphere -- if it has one. Based on dynamical simulations performed using the orbital parameters of the two planets, TOI-6054b, and TOI-6054c are very likely in a 5:3 mean motion resonance. The TOI-6054 system thus has the potential to be an excellent candidate for future atmospheric follow-up observations, with two similarly sized sub-Neptunes around a bright star. We also estimate that if TOI-6054b is currently losing its H/He atmosphere this should be observable from space and from the ground.

astro-ph.EP↗

arXiv2024

Secular Perturbations from Exterior Giants Strongly Influence Gap Complexity in Peas-in-a-Pod Exoplanetary Systems

It has been demonstrated that systems of tightly packed inner planets with giant exterior companions tend to have less regular orbital spacings than those without such companions. We investigate whether this observed increase in the gap complexity of the inner systems can be explained solely as the result of secular dynamics caused by the disturbing potential of the exterior companions. Amplification of mutual orbital inclinations in the inner system due to such secular dynamics may lead to the inner system attaining non-mutually transiting geometries, thereby creating artificial observed gaps that result in a higher calculated gap complexity. Using second-order secular theory, we compute time-averaged observed gap complexities along a favorable line of sight for a set of hypothetical systems, both with and without an outer giant. We find that these secular interactions can significantly contribute to the observed gap complexity dichotomy in tightly packed multiple-planet systems.

astro-ph.EP↗

arXiv2024

History and Habitability of the LP 890-9 Planetary System

We present numerous aspects of the evolution of the LP 890-9 (SPECULOOS-2/TOI-4306) planetary system, focusing on the likelihood that planet c can support life. We find that the host star reaches the main sequence in 1 Gyr and that planet c lies close to the inner boundary of the habitable zone. We find the magma ocean stage can last up to 50 Myr, remove 8 Earth-oceans of water, and leave up to 2000 bars of oxygen in the atmosphere. However, if the planet forms with a hydrogen envelope as small as 0.1 Earth-masses, no water will be lost during the star's pre-main sequence phase from thermal escape processes. We find that the planets are unlikely to be in a 3:1 mean motion resonance and that both planets tidally circularize within 0.5 Gyr when tidal dissipation is held constant. However, if tidal dissipation is a function of mantle temperature and rheology, then we find that planet c's orbit may require more than 7 Gyr to circularize, during which time tidal heating may reach hundreds of terawatts. We thus conclude that the habitability of planet c depends most strongly on the initial volatile content and internal properties, but no data yet preclude the viability of an active biosphere on the planet.

astro-ph.EP↗

arXiv2024

TESS Hunt for Young and Maturing Exoplanets (THYME) XII: A Young Mini-Neptune on the Upper Edge of the Radius Valley in the Hyades Cluster

We present the discovery and characterization of TOI-4364\,b, a young mini-Neptune in the tidal tails of the Hyades cluster, identified through TESS transit observations and ground-based follow-up photometry. The planet orbits a bright M dwarf ($K=9.1$\,mag) at a distance of 44\,pc, with an orbital period of 5.42\,days and an equilibrium temperature of $488^{+4}_{-4}$\,K. The host star's well-constrained age of 710\,Myr makes TOI-4364\,b an exceptional target for studying early planetary evolution around low-mass stars. We determined a planetary radius of $2.01^{+0.1}_{-0.08}$\,Earth radii, indicating that this planet is situated near the upper edge of the radius valley. This suggests that the planet retains a modest H/He envelope. As a result, TOI-4364\,b provides a unique opportunity to explore the transition between rocky super-Earths and gas-rich mini-Neptunes at the early stages of evolution. Its radius, which may still evolve as a result of ongoing atmospheric cooling, contraction, and photoevaporation, further enhances its significance for understanding planetary development. Furthermore, TOI-4364\,b possesses a moderately high Transmission Spectroscopy Metric of 44.2, positioning it as a viable candidate for atmospheric characterization with instruments such as JWST. This target has the potential to offer crucial insights into atmospheric retention and loss in young planetary systems.

astro-ph.EP↗

arXiv2024

The TEMPO Survey II: Science Cases Leveraged from a Proposed 30-Day Time Domain Survey of the Orion Nebula with the Nancy Grace Roman Space Telescope

The TEMPO (Transiting Exosatellites, Moons, and Planets in Orion) Survey is a proposed 30-day observational campaign using the Nancy Grace Roman Space Telescope. By providing deep, high-resolution, short-cadence infrared photometry of a dynamic star-forming region, TEMPO will investigate the demographics of exosatellites orbiting free-floating planets and brown dwarfs -- a largely unexplored discovery space. Here, we present the simulated detection yields of three populations: extrasolar moon analogs orbiting free-floating planets, exosatellites orbiting brown dwarfs, and exoplanets orbiting young stars. Additionally, we outline a comprehensive range of anticipated scientific outcomes accompanying such a survey. These science drivers include: obtaining observational constraints to test prevailing theories of moon, planet, and star formation; directly detecting widely separated exoplanets orbiting young stars; investigating the variability of young stars and brown dwarfs; constraining the low-mass end of the stellar initial mass function; constructing the distribution of dust in the Orion Nebula and mapping evolution in the near-infrared extinction law; mapping emission features that trace the shocked gas in the region; constructing a dynamical map of Orion members using proper motions; and searching for extragalactic sources and transients via deep extragalactic observations reaching a limiting magnitude of $m_{AB}=29.7$\,mag (F146 filter).

astro-ph.EP↗

arXiv2024

Wide Binary Orbits are Preferentially Aligned with the Orbits of Small Planets, but Probably Not Hot Jupiters

Studying the relative orientations of the orbits of exoplanets and wide-orbiting binary companions (semimajor axis greater than 100 AU) can shed light on how planets form and evolve in binary systems. Previous observations by multiple groups discovered a possible alignment between the orbits of visual binaries and the exoplanets that reside in them. In this study, using data from \textit{Gaia} DR3 and TESS, we confirm the existence of an alignment between the orbits of small planets $(R<6 R_\oplus)$ and binary systems with semimajor axes below 700 AU ($p=10^{-6}$). However, we find no statistical evidence for alignment between planet and binary orbits for binary semimajor axes greater than 700 AU, and no evidence for alignment of large, closely-orbiting planets (mostly hot Jupiters) and binaries at any separation. The lack of orbital alignment between our large planet sample and their binary companions appears significantly different from our small planet sample, even taking into account selection effects. Therefore, we conclude that any alignment between wide-binaries and our sample of large planets (predominantly hot Jupiters) is probably not as strong as what we observe for small planets in binaries with semimajor axes less than 700 AU. The difference in the alignment distribution of hot Jupiters and smaller planets may be attributed to the unique evolutionary mechanisms occuring in systems that form hot Jupiters, including potentially destabilizing secular resonances that onset as the protoplanetary disk dissipates and high-eccentricity migration occurring after the disk is gone.

astro-ph.EP↗

arXiv2024

Evaporation of Close-in Sub-Neptunes by Cooling White Dwarfs

Motivated by the recent surge in interest concerning white dwarf (WD) planets, this work presents the first numerical exploration of WD-driven atmospheric escape, whereby the high-energy radiation from a hot/young WD can trigger the outflow of the hydrogen-helium envelope for close-in planets. As a pilot investigation, we focus on two specific cases: a gas giant and a sub-Neptune-sized planet, both orbiting a rapidly cooling WD with mass $M_\ast$ = 0.6 \msun\ and separation $a$ = 0.02 AU. In both cases, the ensuing mass outflow rates exceed $10^{14}$ g sec$^{-1}$ for WD temperatures greater than $T_{\rm WD} \simeq$ 50,000 K. At $T_{\rm WD} \simeq$ 18,000 K [/22,000 K], the sub-Neptune [/gas giant] mass outflow rate approaches $10^{12}$ g sec$^{-1}$, i.e., comparable to the strongest outflows expected from close-in planets around late main-sequence stars. Whereas the gas giant remains virtually unaffected from an evolutionary standpoint, atmospheric escape may have sizable effects for the sub-Neptune, depending on its dynamical history, e.g., assuming that the hydrogen-helium envelope makes up 1 [/4] per cent of the planet mass, the entire envelope would be evaporated away so long as the planet reaches 0.02 AU within the first 230 [/130] Myr of the WD formation. We discuss how these results can be generalized to eccentric orbits with effective semi-major axis $a'=a/(1-e^2)^{1/4}$, which receive the same orbit-averaged irradiation. Extended to a much broader parameter space, this approach can be exploited to model the expected demographics of WD planets as a function of their initial mass, composition and migration history, as well as their potential for habitability.

astro-ph.EP↗