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Abstract It is unclear how directly imaged substellar companions with masses near the deuterium burning limit form, because these objects are rare and their bulk properties are not diagnostic of their formation. In this Letter, we revisit this problem using JWST/NIRCam coronagraphic images of the 29 Cygni (=HIP 99770) system that reveal the recently discovered super-Jovian companion 29 Cyg b at wavelengths covering 4–5μm for the first time. This object has an uncertain mass that straddles the deuterium burning limit (M_b ≃ 15 ± 5M_J) and a low mass ratio with its early-type host star (M_b/M_⋆ ∼ 0.01). Absorption from CO₂and CO is apparent at 4.3 and 4.6μm in our images. The strength of the CO₂feature relative to CO provides strong evidence, based on empirical comparison with literature observations at these wavelengths and atmospheric modeling, that the companion is enriched in heavier elements compared to the roughly solar abundances of the host (Z_b/Z_⋆ = 3 ± 2). In addition, we measure the stellar inclination angle with CHARA/PAVO interferometry: the system is consistent with spin–orbit alignment at the 2σlevel, with Δi = 12° ± 6°. This ensemble of evidence is suggestive of formation within the protoplanetary disk and the rapid accretion of metal-rich material versus disk fragmentation or capture, like higher-mass-ratio companions. 29 Cyg b shows that planet formation around early-type stars can occur on scales at or exceeding the deuterium burning limit, in agreement with the recently revised planetary mass/metallicity trend that predictsZ_pl/Z_⋆ = 3.3 ± 0.5 at high masses from transiting planet densities. 

Abstract HD 143811 AB is the host star to the directly imaged planet HD 143811 AB b, which was recently discovered using data from the Gemini Planet Imager and Keck NIRC2. A member of the Sco-Cen star-forming region with an age of 13 ± 4 Myr, HD 143811 AB is somewhat rare among hosts of directly imaged planets, as it is a close stellar binary, with an ∼18-day period. Accurate values for the orbital and stellar parameters of this binary are needed to understand the formation and evolutionary history of the planet in orbit. We utilize archival high-resolution spectroscopy from FEROS on the MPG/ESO 2.2 m telescope to fit the orbit of the binary, and we combine with unresolved photometry to derive the basic stellar properties of the system. From the orbit, we derive precise values of orbital period of 18.59090 ± 0.00007 days and mass ratio of 0.886 ± 0.003. When combined with stellar evolutionary models, we find masses of both components of $M_{\mathrm{A}}=1.30_{-0.05}^{+0.03}$ M_⊙and $M_{\mathrm{B}}=1.15_{-0.04}^{+0.03}$ M_⊙. While the current data are consistent with the planet and stellar orbits being coplanar, the 3D orientations of both systems are currently poorly constrained, with additional observations required to more rigorously test for coplanarity. 

Abstract We present confirmation of HD 143811 AB b, a substellar companion to spectroscopic binary HD 143811 AB through direct imaging with the Gemini Planet Imager (GPI) and Keck NIRC2. HD 143811 AB was observed as a part of the GPI Exoplanet Survey in 2016 and 2019 and is a member of the Sco-Cen star formation region. The exoplanet is detected ∼430 mas from the host star by GPI. With two GPI epochs and one from Keck/NIRC2 in 2022, we confirm through common proper motion analysis that the object is bound to its host star. We derive an orbit with a semimajor axis of $64_{-14}^{+32}$ au and eccentricity ${0.23}_{-0.16}^{+0.24}$ . Spectral analysis of the GPIH-band spectrum and NIRC2L′photometry provides additional proof that this object is a substellar companion. We compare the spectrum of HD 143811 AB b to PHOENIX stellar models and Exo-Radioactive-Convective Equilibrium Model (REM) exoplanet atmosphere models and find that Exo-REM models provide the best fits to the data. From the Exo-REM models, we derive an effective temperature of $1042_{-132}^{+178}$ K for the planet and translate the derived luminosity of the planet to a mass of 5.6 ± 1.1M_Jupassuming hot-start evolutionary models. HD 143811 AB b is the first directly imaged planet around a binary that is not on an ultrawide orbit. Future characterization of this object will shed light on the formation of planets around binary star systems.