William Thompson

ϵ Eridani b, the nearest known Jupiter analog, has its orbit and mass constrained from radial velocity (RV) and absolute astrometry, and its atmosphere from JWST/NIRCam imaging upper limits in A. Sanghi et al. Here we follow up that work with a self-consistent model of ϵ Eridani b that treats all available data within a single Bayesian framework. We extend the RV data with new measurements, update the treatment of the astrometry data with a new model, and include the NIRCam observations with a grid of evolutionary and atmospheric models. We find a mass of 0.91 ± 0.04 M _Jup and an orbit consistent with previous work. The imaging data helps constrain planet effective temperature, atmospheric metallicity, and surface gravity. The constraints are dependent on model assumptions: for an atmosphere in chemical equilibrium, an otherwise low statistically significant feature in one of the epochs is recovered as the planet at high confidence. When assuming chemical disequilibrium, the posteriors exhibit a bimodal distribution, with one mode consistent with zero flux and the other coinciding with the flux of the tentative feature. Consistent with previous work, the clear atmosphere models are found to be viable at very enhanced metallicity, whereas the cloudy models yield more moderate values. Applying these models to the Roman Coronagraph, we find that the predicted reflected-light fluxes place every cloudy atmosphere our fit allows within the instrument’s expected sensitivity. A nondetection would be very constraining: a final contrast sensitivity of 2 × 10 ⁻⁹ would rule out all cloudy atmospheres under our model assumptions.

The upcoming release of Gaia DR4 will yield thousands of giant planet candidates, eventually enabling studies of giant planet eccentricities, masses, and occurrence rates across a broad range of stellar host masses, metallicities, and ages. However, some of these planet candidates are expected to be false positives and even genuine detections will require additional observations to precisely determine their orbits and masses. We present here the first results of the Gaia Exoplanet Orbits, Demographics, and Evolution Survey, an observational campaign to identify the most promising planet candidate hosts for pre-DR4 vetting and post-DR4 validation and characterization. In this paper, we showcase three systems from our broader sample exhibiting both tangential and radial accelerations, each representing a distinct outcome of our survey strategy. We combine Hipparcos, Hipparcos-Gaia, Gaia DR2, and Gaia DR3 absolute astrometry with adaptive optics (AO) imaging and precision radial velocities (RVs) to constrain companion masses and orbits. HIP 18512, a nearby (15.3 pc) K4V dwarf, hosts a low-mass stellar companion at 10 . ″ 87 ± 0 . ″ 07 (166 au) which produces significant RV and astrometric accelerations on its host star. The RV trend and astrometric acceleration of the nearby (24.2 pc) K4V star HIP 45839, together with an AO imaging nondetection, constrain the companion to a = 17 . 9 − 2.7 + 4.8 au ( P = 70–127 yr) and M = 45 . 2 − 12.7 + 10.5 M _Jup . In the case of HIP 81991 (43.8 pc, G5V), the astrometric and RV data indicate that the companion has a separation of 6 . 4 − 0.3 + 0.6 au ( P = 14.4–17.7 yr) and a mass of 9 . 5 − 2.2 + 5.4 M _Jup , and is more likely a planet (65%) than a brown dwarf (35%).

We present new JWST/NIRCam 4–5 μ m (F410M, F430M) and JWST/MIRI 18–25 μ m (F1800W, F2100W, F2550W) imaging detections of the nearby (3.6 pc) cold (275 K) gas giant exoplanet ϵ Ind Ab. The F2550W detection of ϵ Ind Ab constitutes the longest-wavelength image of an exoplanet acquired to date. Combining three decades of radial velocity (RV) monitoring, Gaia–Hipparcos absolute astrometry, and relative astrometry from direct imaging (including the new NIRCam astrometry), we conduct a comprehensive reanalysis of ϵ Ind Ab’s orbit and obtain a dynamical mass M Ab = 6 . 5 − 0.6 + 0.7 M Jup . Additionally, we demonstrate that the combination of unmodeled stellar activity, partial orbital coverage, and stitching together RVs from different instruments biased the eccentricity in previous orbit fits and led to an incorrect prediction for the planet’s position at the JWST imaging discovery epoch. Using ϵ Ind Ab’s NIRCam and MIRI photometry, we assemble the first 4–25 μ m spectral energy distribution (SED) of a cold gas giant outside the solar system. The NIRCam photometry supports a metal-enriched atmosphere for ϵ Ind Ab based on analysis with atmospheric model grids, consistent with predictions from the giant planet mass–metallicity relation. While the current data do not provide definitive evidence for or against the presence of water ice clouds, we tentatively find that the H ₂ O vapor absorption-dominated F2550W photometry is systematically brighter (>1 σ , but σ ) than predictions from cloud-free/rainout chemistry models and better explained by a cloudy model. We calculate a bolometric luminosity of log L bol / L ⊙ = − 7.23 ± 0.03 dex by directly integrating ϵ Ind Ab’s SED. Combining this with the planet’s dynamical mass and age (3.5 ± 1.0 Gyr), we demonstrate excellent agreement with evolutionary model predictions in a new regime of low luminosities, low masses, and old ages. Our results establish ϵ Ind Ab as a benchmark system for planetary evolution studies and set the stage for the detailed atmospheric characterization of this temperate extrasolar world.

We report the detection of a new brown dwarf companion to HIP 17453 A, a chemically peculiar A0V star located at a distance of 81 pc. HIP 17453 A was observed with high-resolution adaptive-optics imaging using the Near-Infrared Camera 2 on the Keck II telescope as part of the Companions to B and A Stars Snapshot (C-BASS) survey over a 10 yr baseline, revealing the presence of a companion at ~3 arcsec with proper motion consistent with the primary. We estimate the age of the HIP 17453 system as 280 ± 125 Myr, and with follow-up intermediate-resolution ( R ∼ 1800) spectroscopic observations with the Gemini Near-Infrared Spectrograph (GNIRS) on the Gemini North telescope, we found the spectrum of HIP 17453 B to be consistent with a spectral type of L2 ±1. Through interpolation of Sonora Diamondback evolutionary models, we calculate an effective temperature of 195 3 − 78 + 84 K and mass of 5 3 − 8 + 10 M _Jup for HIP 17453 B, which corresponds to a mass ratio of q = 0.024 ± 0.004 for the HIP 17453 system. With its intermediate mass and young age, HIP 17453 B joins a small set of benchmark brown dwarf companions around early-type stars that are suitable for follow-up atmospheric and evolutionary studies.

Gaia Data Release 4 epoch astrometry will enable the detection of thousands of exoplanets through astrometric motion. We present a composite catalog and modeling framework that extracts the maximum information from existing Hipparcos and Gaia data releases. We calibrate Gaia DR2 proper motions and DR3–DR2 scaled position differences against the Gaia DR3 reference frame, and combine these with the Hipparcos-Gaia Catalog of Accelerations (or HGCA), the Hipparcos intermediate astrometric data, Gaia astrometric excess noise, and Gaia radial velocity (RV) variability constraints. We implement a joint likelihood model for these data in Octofitter that marginalizes over Gaia’s unpublished observation epochs. This results in full orbit posteriors that can be computed uniformly for a large class of companions. We compare these posteriors to published orbital solutions for 25 stellar binaries from the Sixth Catalog of Orbits of Visual Binary Stars (or ORB6), recovering all companions at high significance and broadly consistent orbital separations. We then recover independent evidence supporting 94 of 120 tested Jovian exoplanetary systems from the NASA Exoplanet Archive, along with three known stellar companions, while ruling out one previously detected planet. We demonstrate that in cases like 14 Her b, the posteriors confirm the planetary nature of a signal using only Gaia and Hipparcos data. We find no false positives among 25 RV-quiet standard stars without significant Hipparcos-Gaia accelerations. Our method can break degeneracies inherent to proper-motion anomaly or excess-noise modeling alone by resolving orbital curvature within the Gaia baseline. The catalog and updated Octofitter are made publicly available to the community.

We present the most sensitive direct imaging search for the nearest ( d = 3.2 pc) Jupiter-analog exoplanet, ϵ Eri b, with JWST/NIRCam coronagraphy between 4 and 5 μ m (F444W). We achieve a 5 σ contrast sensitivity ≈3.0 × 10 ⁻⁷ (Δ ≈ 16.3 mag) in the F444W filter at the expected planet separation of ≈1″. This is the deepest 4–5 μ m contrast performance achieved for any JWST/NIRCam observation to date at these separations (and >10× better than ground-based limits). Yet, the planet remains elusive to imaging. We update the star’s age to 1.1 ± 0.1 Gyr, older than previous age estimates, using the latest gyrochronology relations. This significantly impacts ϵ Eri b’s inferred effective temperature ( T _eff ), which is now expected to lie between 150 and 200 K based on evolutionary models for a 1 M _Jup planet. Using cloud-free Sonora Flame Skimmer models and custom PICASO patchy cloud models in the above T _eff range, we find that the F444W nondetection of ϵ Eri b can be explained by a metal-enriched atmosphere and/or an atmosphere containing water ice clouds. Both possibilities suggest that ϵ Eri b’s atmosphere is strikingly similar to that of Jupiter in our solar system. Alternatively, if we do not enforce the dynamical mass (0.98 ± 0.09 M _Jup ), a solar metallicity, cloud-free, ≲0.81 M _Jup planet would be consistent with the NIRCam upper limit based on the Sonora Flame Skimmer evolutionary models. Finally, we place limits on the size of a potential ring system using the NIRCam/F210M data and discuss the opportunity to directly image ϵ Eri b with additional JWST observations, the Roman Coronagraph Instrument, the ExtraSolar Coronagraph on the Lazuli Observatory, and EELT/METIS.

We present the OASIS survey program discovery of a substellar companion orbiting the young A1V star HIP 71618, detected using precision astrometry from Gaia and Hipparcos and high-contrast imaging with SCExAO/CHARIS and Keck/NIRC2. Atmospheric modeling favors a spectral type of M5–M8 and a temperature of ∼2700 ± 100 K. Dynamical modeling constrains HIP 71618 B’s mass to be 60 − 21 + 27 M _Jup or 65 − 29 + 54 M _Jup , depending on the adopted companion mass prior. It has a nearly-edge-on 11 au orbit with high eccentricity. HIP 71618 B will be located within the Roman Coronagraph’s dark-hole region during the instrument’s technological demonstration phase. A high-signal-to-noise-ratio detection of HIP 71618 B at 575 nm would demonstrate a 5 σ contrast of 10 ⁻⁷ or better. The system is also located within or very close to the Roman Coronagraph’s Continuous Viewing Zone—near multiple candidate reference stars for dark-hole digging—and its primary is bright ( V ≈ 5). The suitability of HIP 71618 as a potential Roman Coronagraph target for demonstrating the instrument’s core requirement (TTR5) should motivate the timely deep vetting of candidate reference stars.

We present the discovery of a superjovian planet around the young A5 star HIP 54515, detected using precision astrometry from the Hipparcos Gaia Catalogue of Accelerations and high-contrast imaging with SCExAO/CHARIS from the recently commenced OASIS program. SCExAO/CHARIS detects HIP 54515 b in five epochs 0 . ″ 145–0 . ″ 192 from the star (∼3–4 λ / D at 1.65 μ m), exhibiting clockwise orbital motion. HIP 54515 b lies near the M/L transition with a luminosity of log( L / L _⊙ ) ∼−3.52 ± 0.03. Dynamical modeling constrains its mass and mass ratio to be 17.7 − 4.9 + 7.6 M _Jup and 0.0090 − 0.0024 + 0.0036 and favors a ∼25 au semimajor axis. HIP 54515 b adds to a growing list of superjovian planets with moderate eccentricities ( e ≈ 0.4). Now, the third planet discovered from surveys combining high-contrast extreme adaptive optics imaging with precision astrometry, HIP 54515 b, should help improve empirical constraints on the luminosity evolution and eccentricity distribution of the most massive planets. It may also provide a key technical test of the Roman Space Telescope Coronagraph Instrument’s performance in the low stellar flux, small angular separation limit, and a demonstration of its ability to yield constrainable planet spectral properties.

The mature Jovian planet ε Eridani b ( ε Eri b) orbits one of the closest Sun-like stars at a moderate separation of 3.5 au, presenting one of the best opportunities to image a true analog to a solar system planet. We perform a thorough joint reanalysis and cross-validation of all available archival radial velocity (RV) and astrometry data, combining data from eight RV instruments and four astrometric sources (Hipparcos, the Hubble Space Telescope’s Fine Guidance Sensor, Gaia Data Release 2, and Gaia Data Release 3). We incorporate methodological advances that impact our findings, including a principled treatment of correlation between Gaia DR2 and DR3 velocity. We revise the planet’s mass upward to 1.00 ± 0.10 M _{J up} and find that its orbit is nearly circular and likely to be to coplanar with the outer debris disk. We further present one of the first models of an exoplanet orbit exclusively from absolute astrometry and independently confirm the planet’s orbital period. We make specific predictions for the planet’s location at key imaging epochs from past and future observing campaigns. We discuss and resolve tensions between previous works regarding the eccentricity, inclination, and mass. Our results further support that ε Eri b is one of the closest analogs to a solar system planet yet detected around a nearby star.