Noah Vowell

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 _J , P = 7.1 days) 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 ± 3.58 mÅ and an abundance of A(Li) = 2.49 ± 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 _⊕ —an order of magnitude lower than the 5.6 M _J implied by protosolar 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.

We report the discovery of TOI-7019b, the first transiting brown dwarf (BD) known to orbit a star that is part of the Milky Way’s ancient thick disk, as defined chemically ([Fe/H] = −0.79 ± 0.05 dex, [ α /Fe] = +0.26 ± 0.05 dex, [M/H] = −0.59 ± 0.06 dex) and kinematically ( v _⊥ ≈ 150 ± 1 km s ⁻¹ ). We estimate a system age τ = 12 ± 2 Gyr by fitting the host star’s spectrum and spectral energy distribution to alpha-enhanced isochrones and independently using the age−metallicity relation of the thick disk. This makes TOI-7019 by far the most metal-poor and ancient BD host known to date. We measure a BD mass of 61.3 M _J ± 2.1 M _J and radius of 0.82 R _J ± 0.02 R _J from a joint analysis of transit photometry and radial velocity measurements, along with an orbital period of 48.2592 ± 0.0001 days and an orbital eccentricity of 0.403 ± 0.002. The measured radius appears to be 12.3% ± 2.8% larger than predicted relative to standard evolutionary models for old, metal-poor BDs, as well as models that include stellar radiation, hinting at missing physics like the magnetic inhibition of convection. TOI-7019b lowers the probed metallicity regime for transiting BDs by over a factor of two, making it a benchmark system to test evolutionary models in the low-metallicity regime. Future measurements of TOI-7019b’s atmosphere will test whether a BD’s atmospheric composition tracks its host star’s abundances, as expected for binary-like co-formation.

We present a new analysis of the CWW 89 system as part of the Orbital Architectures of Transiting Massive Exoplanets And Low-mass stars (OATMEAL) survey. The CWW 89 system is a member of the 2.8 Gyr old Ruprecht 147 (NGC 6774) cluster and consists of two stars, CWW 89A (EPIC 219388192) and CWW 89B, with the primary hosting a transiting brown dwarf, CWW 89Ab. We use in-transit, highly precise radial velocity measurements with the Keck Planet Finder to characterize the Rossiter–McLaughlin (RM) effect and measure the projected spin–orbit obliquity ∣ λ ∣ = 1 . ° 4 ± 2 . ° 5 and the full 3D spin–orbit obliquity of the brown dwarf to be ψ = 15 . 1 − 10.9 + 15 . 0 ∘ . This value of λ implies that the brown dwarf’s orbit is prograde and well-aligned with the equator of the host star, continuing the trend of transiting brown dwarfs showing a preference for spin–orbit alignment ( λ ≈ 0°) regardless of the stellar effective temperature. This contrast with the transiting giant planet population, whose spin–orbit alignments depend on host T _eff , shows an increasingly clear distinction in the formation and orbital migration mechanisms between transiting giant planets and transiting brown dwarfs like CWW 89Ab. For this system in particular, we find it plausible that the brown dwarf may have undergone coplanar high-eccentricity migration influenced by CWW 89B.

We present the discovery of 11 new transiting brown dwarfs (BDs) and low-mass M dwarfs from NASA’s Transiting Exoplanet Survey Satellite (TESS) mission: TOI-2844, TOI-3122, TOI-3577, TOI-3755, TOI-4462, TOI-4635, TOI-4737, TOI-4759, TOI-5240, TOI-5467, and TOI-5882. They consist of five BD companions and six very-low-mass stellar companions ranging in mass from 25 M _J to 128 M _J. We used a combination of photometric time-series, spectroscopic, and high-resolution imaging follow-up as a part of the TESS Follow-up Observing Program (or TFOP) to characterize each system. With over 50 transiting BDs confirmed, we now have a large enough sample to directly test different formation and evolutionary scenarios. We provide a renewed perspective on the transiting “brown dwarf desert” and its role in differentiating between planetary and stellar formation mechanisms. Our analysis of the eccentricity distribution for the transiting BD sample does not support previous claims of a transition between planetary and stellar formation at ∼42 M _J. We also contribute a first look into the metallicity distribution of transiting companions in the range 7–150 M _J, showing that this does not support a ∼42 M _J transition too. Finally, we also detect a significant lithium absorption feature in one of the BD hosts (TOI-5882). However, we determine that the host star is likely old based on rotation, kinematic, and photometric mdeasurements. We therefore claim that TOI-5882 may be a candidate for planetary engulfment.

We report the discovery and characterization of TOI-2005 b, a warm Jupiter on an eccentric (e ∼ 0.59), 17.3 days orbit around a V _mag = 9.867 rapidly rotating F-star. The object was detected as a candidate by Transiting Exoplanet Survey Satellite and the planetary nature of TOI-2005 b was then confirmed via a series of ground-based photometric, spectroscopic, and diffraction-limited imaging observations. The planet was found to reside in a low sky-projected stellar obliquity orbit (λ = 4 . 8 − 2.5 + 2.3 degrees) via a transit spectroscopic observation using the Magellan Magellan Inamori Kyocera Echelle spectrograph. TOI-2005 b is one of a few planets known to have a low-obliquity high-eccentricity orbit, which may be the result of high-eccentricity coplanar migration. The planet has a periastron equilibrium temperature of ∼2100 K, similar to some highly irradiated hot Jupiters where atomic metal species have been detected in transmission spectroscopy, and varies by almost 1000 K during its orbit. Future observations of the atmosphere of TOI-2005b can inform us about its radiative timescales thanks to the rapid heating and cooling of the planet.