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Abstract We present a direct imaging study of V892 Tau, a young Herbig Ae/Be star with a close-in stellar companion and circumbinary disk. Our observations consist of images acquired via Keck II/NIRC2 with nonredundant masking and the pyramid wavefront sensor at $K\prime$band (2.12μm) and $L\prime$band (3.78μm). Sensitivity to low-mass accreting companions and cool disk material is high at $L\prime$band, while complimentary observations at $K\prime$band probe hotter material with higher angular resolution. These multiwavelength, multiepoch data allow us to differentiate the secondary stellar emission from disk emission and deeply probe the structure of the circumbinary disk at small angular separations. We constrain architectural properties of the system by fitting geometric disk and companion models to the $K\prime$- and $L\prime$-band data. From these models, we constrain the astrometric and photometric properties of the stellar binary and update the orbit, placing the tightest estimates to date on the V892 Tau orbital parameters. We also constrain the geometric structure of the circumbinary disk, and resolve a circumprimary disk for the first time. 

Abstract We present the highest-angular-resolution infrared monitoring of LkCa 15, a young solar analog hosting a transition disk. This system has been the subject of a number of direct-imaging studies from the millimeter through the optical, which have revealed multiple protoplanetary disk rings as well as three orbiting protoplanet candidates detected in infrared continuum emission (one of which was simultaneously seen at Hα). We use high-angular-resolution infrared imaging from 2014 to 2020 to systematically monitor these infrared signals and determine their physical origin. We find that three self-luminous protoplanets cannot explain the positional evolution of the infrared sources since the longer time baseline images lack the coherent orbital motion that would be expected for companions. However, the data still strongly prefer a time-variable morphology that cannot be reproduced by static scattered-light disk models. The multiepoch observations suggest the presence of complex and dynamic substructures moving through the forward-scattering side of the disk at ∼20 au or quickly varying shadowing by closer-in material. We explore whether the previous Hαdetection of one candidate would be inconsistent with this scenario and in the process develop an analytical signal-to-noise penalty for Hαexcesses detected near forward-scattered light. Under these new noise considerations, the Hαdetection is not strongly inconsistent with forward scattering, making the dynamic LkCa 15 disk a natural explanation for both the infrared and Hαdata. 

Abstract We present medium-resolution ( λ /Δ λ  = 2700), near-infrared spectral standards for field L0–L2, L4, and L7–Y0 dwarfs obtained with the Near-Infrared Echellette Spectrometer on the Keck II 10 m telescope. These standards allow for detailed spectral comparative analysis of cold brown dwarfs discovered through ongoing ground-based projects such as Backyard Worlds: Planet 9, and forthcoming space-based spectral surveys such as the James Webb Space Telescope, SPHEREx, Euclid, and the Nancy Grace Roman Space Telescope. 

Since the start of science operations in 1993, the twin 10-meter W. M. Keck Observatory (WMKO) telescopes have continued to maximize their scientific impact and to produce transformative discoveries that keep the observing community on the frontiers of astronomical research. Upgraded capabilities and new instrumentation are provided though collaborative partnerships with Caltech, the University of California, and the University of Hawaii instrument development teams, as well as industry and other organizations. This paper summarizes the performance of recently commissioned infrastructure projects, technology upgrades, and new additions to the suite of observatory instrumentation. We also provide a status of projects currently in design or development phases and, since we keep our eye on the future, summarize projects in exploratory phases that originate from our 2022 strategic plan developed in collaboration with our science community to adapt and respond to evolving science needs. 

Abstract Using the Keck Planet Imager and Characterizer, we obtained high-resolution (R∼ 35,000)K-band spectra of the four planets orbiting HR 8799. We clearly detected H₂O and CO in the atmospheres of HR 8799 c, d, and e, and tentatively detected a combination of CO and H₂O in b. These are the most challenging directly imaged exoplanets that have been observed at high spectral resolution to date when considering both their angular separations and flux ratios. We developed a forward-modeling framework that allows us to jointly fit the spectra of the planets and the diffracted starlight simultaneously in a likelihood-based approach and obtained posterior probabilities on their effective temperatures, surface gravities, radial velocities, and spins. We measured $v\sin \left(i\right)$values of ${10.1}_{-2.7}^{+2.8}\mathrm{km}{\mathrm{s}}^{-1}$for HR 8799 d and ${15.0}_{-2.6}^{+2.3}\mathrm{km}{\mathrm{s}}^{-1}$for HR 8799 e, and placed an upper limit of <14 km s⁻¹of HR 8799 c. Under two different assumptions of their obliquities, we found tentative evidence that rotation velocity is anticorrelated with companion mass, which could indicate that magnetic braking with a circumplanetary disk at early times is less efficient at spinning down lower-mass planets.