arXiv subjects

Andrew Vanderburg

Publications and source records attributed to Andrew Vanderburg.

At least 19 recordsLinked to original sources

arXiv2026

Six New Eclipsing AM CVn Binaries from the Zwicky Transient Facility

We present the discovery of six new eclipsing AM CVn binaries, helium-accreting ultracompact systems in which a cool donor eclipses the accreting white dwarf. The systems were found in a GPU-accelerated Box Least Squares (BLS) search of Zwicky Transient Facility (ZTF) photometry and have orbital periods of 39.3 to 59.9 minutes. We obtained spectroscopy with the Low Resolution Imaging Spectrometer (LRIS) on the Keck I telescope for all six systems, and every spectrum shows helium emission with no detectable hydrogen, confirming their AM CVn classification. Our discoveries increase the number of deeply eclipsing AM CVn from 11 to 17 (i.e., systems in which the accreting white dwarf is both the dominant source of optical light and eclipsed by the donor). With high-speed photometric follow-up, these systems will provide the mass ratios, inclinations, and fractional radii of both components. They will also provide new tests of AM CVn formation models and stronger constraints on the long-term evolution of these sources.

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arXiv2026

Planets surviving common envelope evolution should be rare, massive, and orbit very close to their host star

The discovery of exoplanets around white dwarfs uniquely informs our understanding of planetary survival through stellar evolution. Common Envelope (CE) evolution is one of the proposed mechanisms that could shape the orbital architecture of these planets around stellar remnants. In this work, we predict the occurrence rate and orbital separation/planet mass distributions for planets that could form around white dwarfs through CE evolution. We simulate populations of giant-planet systems, sampling initial conditions from observed mass and semi-major axis distributions for main sequence stars. We evolve the host star from main sequence to white dwarf to assess which planetary configurations could survive, and we predict the resulting post-CE planet population. Our results suggest that such planets should be rare, massive, and have very close orbital separations. We find that most of the surviving planets have masses of $>10\,M_{\rm{Jup}}$ and orbital separations $<1.4$ times the tidal disruption radius, $a_{disrupt}$ ($\lesssim0.006$ AU, also called the Roche limit), which is in contrast to high eccentricity migration, which produces planets with orbital separations $>2a_{disrupt}$. The properties of CE survivors from our simulations contrast with the known closely-orbiting planet WD 1856+534 b, suggesting a different mechanism may be responsible for its formation.

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arXiv2026

A Sample of Thick-Disk Stars Hosting Hot Jupiters

We present a homogeneous analysis of 268 confirmed and candidate transiting hot-Jupiter host stars with 4800K < Teff < 6200K. We combine high-resolution TRES spectra, Gaia, 2MASS and WISE photometry, and Gaia astrometry to determine these stars' Teff, log g, Rstar, [alpha/Fe] and [Fe/H]. Based on their [alpha/Fe] and [Fe/H], we classify the stars as members of the Milky Way's low-[alpha/Fe] thin disk, high-[alpha/Fe] thick disk or an ambiguous intermediate population. We identify two confirmed hot Jupiters (WASP-81 b and TOI-5322 b) and three candidate hot Jupiters (TOI-3118.01, TOI-2728.01, and TOI-5781.01) as orbiting previously-unrecognized members of the high-alpha thick disk. We compare the properties of the confirmed planets in the three populations and note two indications of a potential difference between the populations: both high-[alpha/Fe] confirmed planets and eight out of the eleven ambiguous-disk confirmed planets are less massive than the median low-[alpha/Fe] planet, and none of our high-[alpha/Fe] or ambiguous confirmed planets have orbital periods shorter than 2.7 d, when 22% of our low-[alpha/Fe] population do. These differences may reflect variations in giant-planet formation across galactic environments, evolutionary effects, or differing stellar properties between the high- and low-[alpha/Fe] populations. Our catalog is the largest sample of chemically-identified high-[alpha/Fe] thick-disk confirmed and candidate hot-Jupiter host stars. These ancient systems, with ages > 8 Gyr, may allow for a better understanding of how the formation of hot Jupiters depends on galactic environment, and how their orbits evolve over very long time scales.

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arXiv2026

HD 715 b, a Warm Jupiter Orbiting a Massive Subgiant Discovered from a Single TESS Transit

Transiting Warm Jupiters orbiting bright stars are scarcely known, but a substantial number of these planets have been uncovered by the TESS mission. In this work we report the discovery and confirmation of a transiting Warm Jupiter orbiting the bright ($V$ = 8.70) subgiant star HD 715 (TOI-6893). HD 715 b was originally identified from a single transit event in TESS Sector 70. We acquired two seasons of radial velocity follow-up using the PFS, TRES, and MINERVA-Australis spectrographs, which clearly detect the planetary orbit. At $M_*=1.60\pm0.04 M_\odot$, HD 715 thus becomes one of the most massive stars known to host a transiting Warm Jupiter. From a joint fit to the TESS transit and our RVs, we find that HD 715 b has a $56.40^{+0.19}_{-0.23}$ day orbital period and measure a precise mass and radius of $0.635\pm0.056 M_J$ and $1.07\pm0.04 R_J$, rendering it a relatively typical member of the Warm Jupiter population. The moderate orbital eccentricity of $0.21^{+0.07}_{-0.08}$ contrasts with the higher eccentricities of other similar Warm Jupiters orbiting evolved stars, indicating a greater diversity in orbital eccentricities than previously known. The absence of additional transits in preceding TESS observations in Sectors 42 and 43 allows us to further refine the range of possible orbital periods to $[56.01, 56.35]$ days. Though the ephemeris uncertainty remains substantial, future photometric observations may nonetheless allow for recovery of the transit of HD 715 b.

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arXiv2026

Toddlers in Resonance I: low masses and eccentricities of the 17 Myr giant planets HIP 67522 bc from transit timing variations

Infant ($<$100\,Myr) transiting planet systems provide glimpses into the processes that shape the observed mature planet population. Masses for these planets are powerful data points for testing theories of planet formation and evolution. Because young systems tend to be in mean-motion resonances (MMR) and show higher rates of transit timing variations (TTVs), we can take advantage of deviations in the expected versus observed transit timings due to gravitational interactions between the planets to determine the planetary masses and orbital eccentricities. Here we report the TTV analysis of HIP\,67522, a 17\,Myr two-planet system near a 2:1 orbital resonance. The analysis is based on 55 transit observations (50 epochs) of planet b and 29 transit observations (22 epochs) of planet c, taken across 11 facilities. Assuming circular orbits, we determine masses of $M_b=25.0^{+7.6}_{-7.8}M_\oplus$ and $M_c=11.2\pm1.4M_\oplus$. Allowing for eccentric orbits, we find $M_b=23.1^{+15.4}_{-12.4}M_\oplus$ and $M_c=11.8^{+3.0}_{-2.3}M_\oplus$, and low eccentricities ($<0.1$) for both planets. Adopting a Gaussian prior on $M_b$ from the JWST transmission spectrum tightens the eccentric-solution mass for planet c to $9.7^{+1.9}_{-1.6}M_\oplus$, which is our recommended solution. The low masses and large radii are consistent with a contracting atmosphere planet formation model, such as Gas Dwarf formation. Given the challenge of radial-velocity masses and the high rate of TTVs seen in young systems, TTV-masses will be essential for testing theories of the formation and evolution of super-Earths and sub-Neptunes and determining the conditions that create the most common types of planets in the Galaxy.

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arXiv2026

The First Hubble Detection of a Secondary Eclipse from a Rocky Exoplanet: the 5.4-hour planet TOI-2431 b

We present an HST/WFC3 G141 phase-curve observation of the ultra-short-period rocky planet TOI-2431 b and detect its secondary eclipse in the near infrared. Combined with the TESS optical eclipse, these measurements constrain the planet's dayside brightness temperature, reflected light contribution, albedo, and heat redistribution. We detect the eclipse in the optical and near infrared wavelengths of TESS and HST/WFC3 G141, with a planet-to-star flux ratio of 37+/-10 ppm and 69(+14/-13) ppm, respectively. Assuming negligible reflected light, the joint TESS+HST fit yields a brightness temperature T_b,joint=2524(+77/-84) K and a brightness temperature ratio of R_joint=T_b,joint/T_p,max=0.980(+0.032/-0.034) consistent with the zero-albedo, no-redistribution limit T_p,max=2574(+36/-35) K. The HST phase curve is consistent with zero nightside emission and no measurable hotspot offset, consistent with inefficient day-night heat distribution. Under this thermal-dominated interpretation, TOI-2431 b lies at the zero-albedo, no-redistribution limit and contrasts with previously observed lava worlds. At optical and near-infrared wavelengths, however, thermal emission is degenerate with reflected light. For a geometric albedo of A_g=0.1, reflected light would contribute approximately 11 ppm in each bandpass, reducing the temperature to T_b,joint(A_g=0.1)=2407(+91/-102) K. Longer-wavelength observations are required to isolate the thermal component. Planned JWST/MIRI LRS observations are expected to substantially reduce this degeneracy and provide more direct constraints on heat redistribution and possible silicate-atmosphere spectral features. This marks the first secondary eclipse detection of a rocky exoplanet using HST and establishes TOI-2431 b as a benchmark target for studying properties of lava worlds.

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arXiv2026

A Binary Flux Calibrator Reveals the Scientific Potential of Short-integration JWST MIRI Imaging to Directly Detect sub-Jupiter Exoplanets

We report the direct imaging detection of a stellar companion to HD 101452 (HIP 56925; Gaia DR3 5384905720847544192), an A star historically used as an infrared flux calibrator. The companion was identified from an asymmetry in the stellar PSF using short-integration (<1 min), noncoronagraphic JWST MIRI imaging from 15 - 25.5$μ$m that was obtained as part of the absolute flux calibration program CAL 4496. We detect the stellar companion in four MIRI imaging filters at a projected separation of 1.3 arcsec with a mid-infrared flux ratio of approximately $27\times$ warranting its removal from the ensemble of JWST flux calibrator systems. This detection also demonstrates that noncoronagraphic MIRI imaging can recover companions at separations below $3λ/D$ when a reference star with a closely matched flux level to the science target is available. Using the measured contrast curves from the calibration data, we evaluate the predicted sensitivity achievable with similar short MIRI observations for nearby stars (<30 pc) that are of interest to the direct-imaging community with comparable brightness to HD 101452 (W4 ~ 6.8 mag). We find that integrations of only 17-42 s are be capable of detecting sub-Jupiter-mass planets at solar system-like separations around a subset of neighboring systems if the PSF subtraction is conducted with closely flux-matched references. These results demonstrate that minutes-length, noncoronagraphic MIRI observations can provide a powerful and efficient new avenue for exploring the cold giant planet population around nearby stars.

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arXiv2026

Discovery and Characterization of the TOI-4468 Planetary System: A Transiting Hot Jupiter With a Lone Nearby Outer Companion

We report the discovery of two planets, a hot Jupiter and a nearby outer sub-Neptune, orbiting the star TOI-4468. This system is unique among the current exoplanet census in that it features a close outer companion to a hot Jupiter without an accompanying inner companion. By jointly fitting radial velocity measurements taken with the NEID spectrograph and transit photometry from TESS and several ground-based observatories, we constrain the orbital periods, masses, and radii of these two planets. We confirm the planetary nature of the hot Jupiter TOI-4468 b ($R = 1.01 R_J$, $m = 0.54 M_J$, $P = 2.77$ days). We also validate the outer planet TOI-4468 c ($R = 0.28 R_J$, $P = 7.01$ days) statistically, incorporating constraints from ground-based observations. We also identify, but cannot confirm, an additional radial velocity signal which may be due to an outer giant in this system with an orbital period of 624 days. From the observed geometry of this system, we argue that it must never have encountered an early secular resonance that is thought to excite the mutual inclination of other hot Jupiter/outer companion systems. We discuss the possibility of an undetected inner companion, as well as potential implications for hot Jupiter formation.

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arXiv2026

Atmospheric Signatures of Common Envelope Evolution in White Dwarf Planets

The majority of confirmed exoplanets orbit within 1 au of a main-sequence (MS) star. When their stellar hosts evolve off the MS, many of these planets will be engulfed and destroyed, creating empty "forbidden" zones around the stars as they evolve to their final state as a white dwarf (WD). However, several confirmed and candidate WD planets have been found within this forbidden zone. Two formation scenarios have been proposed to explain the existence of these close-in planets: high-eccentricity migration and common envelope evolution (CEE). There are currently few observational tests to distinguish between these pathways. In this study, we investigate whether CEE could leave a detectable atmospheric signature. Using Modules for Experiments in Stellar Astrophysics (MESA) models, we simulate an engulfed planet inspiraling into an AGB star, and allow the planet to accrete mass via Bondi-Hoyle-Lyttleton accretion. Assuming a range of planet masses (1$-$13 M$_{\mathrm{Jup}}$) and accretion efficiencies (0.01$-$1.0), we find that the planet can accrete up to 48% of its initial mass in the most extreme Eddington-limited scenario. Because this accreted material is enriched in hydrogen and helium, we expect it to decrease the planet's bulk metallicity. Using simulated emission spectra, we find that CEE can increase thermal emission by up to 9.0% for a cool planet such as WD 1856 b. For lower accretion efficiencies (0.01$-$0.5), thermal emission increases between 0.1$-$3.6%. This signature may be observable in the most favorable cases, providing a potential new probe for investigating the dynamical history of close-in planets around WDs.

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arXiv2026

The JWST Search for Earth-Luna Analogs: Upper Limits on Exomoons and Refined Ephemerides for TOI 700 d and e

While no conclusive detections of exomoons have been reported to date, planet formation theories predict that Luna-analog satellites should be a common outcome of the collisional dynamics in early extrasolar systems. Such satellites have the potential to unlock new avenues to learn about exoplanet systems, speaking to topics of habitability, tidal heating, planet formation, late-stage growth, planetary compositions, and more. Here we describe the results of our JWST program to search for Luna-analog exomoons around the rocky, habitable-zone M-dwarf planets TOI 700 d and e. We refine the ephemerides of both worlds, providing an order-of-magnitude improvement in period precision and a factor of 2-3 improvement in planetary radii. We identify a strong correlated noise signal with a timescale of $16\pm4$ minutes and an amplitude of $46\pm4$ ppm; similar signals have been observed in previous JWST analyses of other stars and have been ascribed to stellar granulation. This noise source inflates our error by a factor of 4 relative to photon-noise expectations in 10-minute bins and limits our sensitivity to moons: we determine that our observations are sensitive mainly to moons larger than Ganymede on periods longer than 2 days (i.e., moons larger than our solar system's natural satellites). If this noise could be corrected, we would be sensitive to Luna-analog moons. Future work to address this noise source will thus be critical for detecting exomoons in stellar transits, as well as for all other science cases that hope to take advantage of JWST white-light curves in the photon-noise limit.

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arXiv2026

Understanding eccentric temperate giants: an in-depth study of the architecture and stellar obliquity of the TOI-2134 system

We revisit the TOI-2134 planetary system with three new high-cadence TESS sectors and 98 more spectra. This new analysis confirms the two orbiting planets by simultaneously modelling a total of eight sectors of corrected TESS photometry and 280 HARPS-N and SOPHIE radial velocities: an inner mini-Neptune in a near-circular $9.229198\pm0.000003$ days orbit, and an outer temperate sub-Saturn orbiting with a $95.852840\pm0.000042$ days period and eccentricity of $0.31\pm0.01$. The masses and radii of the planets were computed to be $9.37\pm0.54$ Me and $2.735\pm0.068$ Re for planet b, and $58.3\pm1.9$ Me and $7.35\pm0.18$ Re for planet c. The new data not only improves the detection significance and precisions on the planetary orbits, but also breaks the original multimodality in the eccentricity solution for the outer planet. We also detect a long-term trend in the radial velocity data, which we attribute to a stellar magnetic cycle. We investigate the spin-orbit alignment of the system via observations of the Rossiter-McLaughlin effect for TOI-2134~b with EXPRES and TOI-2134~c with PARAS-2. No RM effect was detected for planet b, but we find a 4.7$σ$ detection of a $59\pm31^{\circ}$ obliquity for planet c. Finally, we examine the architecture of the system, assess its completeness, investigate the planetary interior, and their suitability for follow-up atmospheric analysis.

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arXiv2026

The KPF SURFS-UP Survey I: Transmission Spectroscopy of WASP-76 b

We introduce the KPF SURFS-UP (Spectroscopy of the Upper-atmospheres and ReFractory Species in Ultra-hot Planets) Survey, a high-resolution survey to investigate the atmospheric composition and dynamics of a sample of ultra-hot Jupiters with the Keck Planet Finder (KPF). Due to the unique design of KPF, we developed a publicly available pipeline for KPF that performs blaze removal, continuum normalization, order stitching, science spectra combination, telluric correction, and atmospheric detection via cross-correlation. As a first demonstration, we applied this pipeline to a transit of WASP-76 b and achieved some of the highest signal-to-noise detections of refractory species in WASP-76 b to date (e.g., Fe I is detected at a SNR of 14.5). We confirm previous observations of an asymmetry in Fe I absorption, but find no measurable ingress-egress asymmetry in Na I and Ca II. Together, these results suggest variations within different layers of the atmosphere of WASP-76 b: neutral metals such as Fe I trace deeper regions with stronger asymmetries, while Na I and Ca II probe regions higher in the atmosphere where the ingress-egress asymmetries are weaker. Unlike some other ultra-hot Jupiters, our results are qualitatively consistent with GCM predictions of decreasing velocity asymmetry with altitude and do not require a high-altitude super-rotating jet that has been invoked for other planets (e.g., WASP-121 b). These results suggest that atmospheric circulation patterns in ultra-hot Jupiters may be more diverse than previously thought, highlighting the need for broader surveys to study how atmospheric dynamics depend on planetary and stellar properties.

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arXiv2026

Kepler Image-Subtracted Light Curves and Variable Star Catalog of NGC 6819

Variable stars in open clusters are valuable probes of stellar evolution. They provide precise measurements of stellar properties, constrain cluster ages and distances, and trace the angular momentum evolution of stellar populations. To advance these studies, we applied image subtraction and systematic reduction techniques to the NGC 6819 Kepler superstamp time-series data (Quarters 1-16), using the Gaia DR3 catalog to identify the positions of individual sources. We produce 81,498 high-precision light curves for 11,055 sources in the crowded field harboring the 2.5 Gyr open cluster NGC 6819. Our detrended light curves achieve a best root-mean-square precision of 33 ppm (6.5-hour bins) for stars with Kepler magnitudes 12 - 12.5 mag, falling to 79 ppm at 14 - 14.5 mag. Using Gaia DR3 proper motions, and parallaxes, we distinguished likely cluster members from field stars. We identified and classified 87 periodic variables that are potential members of NGC 6819, including 26 newly-discovered variables. We make our light curves and variable classifications publicly available to enable further studies of stellar variability and angular momentum evolution in this intermediate-aged open cluster.

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arXiv2026

Stellar Obliquities of Young Systems, Atmospheres Undergoing Contraction and Escape (SOYSAUCE) II: a 135 Myr planet on an aligned orbit with transit timing variations

Young planets (<1 Gyr) provide opportunities to directly probe planet formation and evolution processes in action. However, due to heightened stellar activity, there is a lack of known transiting planets in adolescence (~100-500 Myr). Here we present the validation of TIC 150070085 b, a 3.6 R_E planet on a 10.47 day orbit, and report the candidate TIC 150070085 c, a 3.0 R_E planet on a 15.90 day orbit. While we are unable to validate the second signal, the proximity to mean motion resonance (3:2) and transit timing variations observed in the transits of TIC 150070085 b strongly suggest the signal is planetary. We confirm the host star as a member of Alessi 84 and combine the group's CMD, rotation, and variability properties to update the age to 135 +/- 10 Myr. We additionally use MAROON-X to observe the Rossiter-McLaughlin signal of TIC 150070085 b and measure the sky projected obliquity angle ($λ$). We find TIC 150070085 b is consistent with a near-aligned orbit with its host star (|$λ$| = 18 +/- 12$^\circ$), in line with similarly aged transiting planets with measured $λ$ values. Continued discovery and characterization of planets in this age regime are vital to link planetary infancy (<50 Myr) and maturity (>1 Gyr).

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arXiv2026

A Search for Wide-orbit Planets Around M-dwarfs using Deep MIRI 15-micron Images

Wide-orbit ($>$10 AU) gas giant planets shape the architecture of planetary systems, yet their occurrence rate remains poorly constrained. JWST has obtained the deepest mid-infrared images of nearby stars to date through substantial MIRI time-series observations of transiting planets, providing sensitive probes for wide-orbit companions. Here we leverage 15 micron observations from four programs targeting ten M-dwarf systems to search for such planets. By applying reference differential imaging for precise PSF subtraction, we achieve a 5$σ$ contrast of $8.9 \times 10^{-4} - 6.2 \times 10^{-3}$ (sensitivity in apparent magnitude of 14.8-15.8 mag) at a separation of 1" and $1.2 -9.1 \times 10^{-4}$ (16.5-17.9 mag) at separations $\gtrsim$3". The sensitivity is converted to planet detection probability for each system as a function of planet mass versus semimajor axis. Assuming solar metallicity and a clear atmosphere, we are sensitive to Jupiter-sized planets with an effective temperature of ${\sim}$233 K at separations beyond 20 AU in systems at 12.5 pc. Additionally, we catalog the nearby sources and estimate their possible impact on future observations assuming they are background sources. Our results demonstrate that archival MIRI time-series imaging data is a powerful window into the population of wide-orbit gas giants around M-dwarfs.

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arXiv2026

Lithium Enrichment in a Subgiant Star with a Brown Dwarf Companion: A Planetary Engulfment Candidate

Theoretical models predict that subgiants within a narrow mass regime can retain detectable lithium enrichment signatures from planetary engulfment. We test this prediction using TOI-5882, selected because it occupies this favorable subgiant parameter space and hosts a massive brown dwarf ($22 \, M_{ \rm J}$, $P=7.1 \,{\rm d}$) companion capable of dynamically perturbing inner planets. We investigate whether: (1) TOI-5882 exhibits lithium enhancement among similar subgiants, (2) planetary material would be deposited in the convective zone, and (3) the required engulfed mass lies within a plausible range for planetary engulfment. Using spectra from the Tillinghast Reflector Echelle Spectrograph, we measured a Li I equivalent width of $75.39 \pm 3.58$ mA and an abundance of A(Li) $=2.49 \pm 0.12$ dex. Comparing these values to a control sample of 61 subgiants from the GALactic Archaeology with HERMES (GALAH) DR4 survey, we find that TOI-5882 ranks in the 98.4th percentile in both metrics, confirming significant lithium enrichment. We evaluate the engulfment scenario by modeling convective zone deposition and estimating the mass required to reproduce the observed enhancement relative to the control sample. We perform an estimate of the engulfed planetary mass incorporating CI chondritic Li abundances, as planets formed via core accretion are enriched in heavy elements and lithium partitions with these metals. This yields a required engulfed mass of $9$-$95\,M_\oplus$--an order of magnitude lower than the $5.6 \, M_{\rm J}$ implied by proto-solar assumptions. TOI-5882's lithium excess can plausibly result from the ingestion of a super-Earth to Neptune-mass planet, motivating further studies to test this scenario.

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arXiv2026

JWST unveils a high mean molecular weight atmosphere for mini-Neptune TOI-1130b: Evidence for formation beyond the water ice line

We present the combined JWST/NIRSpec G395H and NIRISS SOSS transmission spectrum of a warm mini-Neptune, TOI-1130b (3.66 R$_{\oplus}$, 19.8 M$_{\oplus}$, $T_{eq}\sim825$ K). It is part of a rare and unique multi-planet system TOI-1130, which hosts an inner mini-Neptune and an outer hot Jupiter locked in a 2:1 mean motion resonance. From the transmission spectrum of TOI-1130b we detect multiple molecules -- H$_2$O (7.5$σ$), CO$_2$ (3.3$σ$), and SO$_2$ (3.6$σ$), as well as a tentative detection of CH$_4$ ($\sim$2$σ$). We find a strong optical slope in the NIRISS/SOSS spectrum, which is consistent with TESS and CHEOPS transit depth measurements. From equilibrium chemistry retrievals we measure the atmospheric metallicity ($\log{Z/Z_{\odot}}=1.8^{+0.4}_{-0.3}$) and C/O ratio ($<$0.75 at 3$σ$ level confidence) and constrain the atmospheric mean molecular weight, $μ$ = 5.5$^{+1.3}_{-0.8}$ amu. These constraints are consistent with self-consistent forward model grids. We detect no significant He I 1.083$μ$m absorption signal and put a mass-loss rate upper limit of $10^{11}$g\s$^{-1}$. The volatile-rich high mean molecular weight atmosphere of TOI-1130b along with the `pebble-filtering' effect of the outer hot Jupiter supports the ex-situ formation scenario beyond the water ice line and subsequent migration, coherent with its present orbital architecture. A volatile-rich formation scenario could also potentially explain the location of TOI-1130b at the edge of the `radius cliff'. This result hints that the mini-Neptune population may not a homogeneous formation history; rather, volatile-rich ex-situ formation also contributes to its population.

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arXiv2026

Direct Imaging Constraints on Binary Planets and Exomoons around Epsilon Indi A b

Epsilon Indi A b is a directly imaged $\sim6 M_{\rm Jup}$ exoplanet orbiting a nearby (3.6 pc) K-dwarf at $\sim 30$ AU. We analyze archival JWST/MIRI 15 $μ$m coronagraphic imaging of this planet to search for directly imaged satellites orbiting Eps Ind A b. Within the planet's Hill sphere (radius $R_H \approx 2.3$ AU or $1.3 λ/D$), we compare single- and double-PSF models using Bayesian evidence. We find that a double-PSF (binary planet) fit is preferred. This apparent preference can most plausibly be explained by systematics, although follow-up observations would be required to fully rule out a binary planet interpretation. We construct a contrast curve of the exoplanet after removing this feature, demonstrating sensitivity to companions as faint as $0.03\times$ the F1550C flux of Eps Ind A b (equivalent to $T = 130$ K, $1.3 M_{\rm Jup}$) at large separations (>2 AU). We also demonstrate sensitivity to brighter companions $0.2\times$ the F1550C flux of Eps Ind A b (equivalent to $T = 180$ K, $2.5 M_{\rm Jup}$) down to separations of 0.52 AU (1.3 pixels; $0.29 λ/D$; 144 mas). This study demonstrates that JWST/MIRI can directly detect exomoons or binary planets inside the Hill sphere of directly imaged exoplanets orbiting neighboring stars.

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