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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 The stellar cluster environment is expected to play a central role in the evolution of circumstellar disks. We use thermochemical modeling to constrain the dust and gas masses, disk sizes, UV and X-ray radiation fields, viewing geometries, and central stellar masses of 20 class II disks in the Orion Nebula Cluster (ONC). We fit a large grid of disk models to 350 GHz continuum, CO J = 3 − 2, and HCO + J = 4 − 3 Atacama Large Millimeter/submillimeter Array observations of each target, and we introduce a procedure for modeling interferometric observations of gas disks detected in absorption against a bright molecular cloud background. We find that the ONC disks are massive and compact, with typical radii <100 au, gas masses ≥10 −3 M ⊙ , and gas-to-dust ratios ≥100. The interstellar‐medium‐like gas-to-dust ratios derived from our modeling suggest that compact, externally irradiated disks in the ONC are less prone to gas-phase CO depletion than the massive and extended gas disks that are commonly found in nearby low-mass star-forming regions. The presence of massive gas disks indicates that external photoevaporation may have only recently begun operating in the ONC; though it remains unclear whether other cluster members are older and more evaporated than the ones in our sample. Finally, we compare our dynamically derived stellar masses with the stellar masses predicted from evolutionary models and find excellent agreement. Our study has significantly increased the number of dynamical mass measurements in the mass range ≤0.5 M ⊙ , demonstrating that the ONC is an ideal region for obtaining large samples of dynamical mass measurements toward low-mass M-dwarfs. 

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 The Orion Nebula Cluster (ONC) hosts protoplanetary disks experiencing external photoevaporation by the cluster’s intense UV field. These “proplyds” are comprised of a disk surrounded by an ionization front. We present ALMA Band 3 (3.1 mm) continuum observations of 12 proplyds. Thermal emission from the dust disks and free–free emission from the ionization fronts are both detected, and the high-resolution (0.″057) of the observations allows us to spatially isolate these two components. The morphology is unique compared to images at shorter (sub)millimeter wavelengths, which only detect the disks, and images at longer centimeter wavelengths, which only detect the ionization fronts. The disks are small (r_d= 6.4–38 au), likely due to truncation by ongoing photoevaporation. They have low spectral indices (α≲ 2.1) measured between Bands 7 and 3, suggesting the dust emission is optically thick. They harbor tens of Earth masses of dust as computed from the millimeter flux using the standard method although their true masses may be larger due to the high optical depth. We derive their photoevaporative mass-loss rates in two ways: first, by invoking ionization equilibrium and second, by using the brightness of the free–free emission to compute the density of the outflow. We find decent agreement between these measurements and $\dot{M}$= 0.6–18.4 × 10⁻⁷M_⊙yr⁻¹. The photoevaporation timescales are generally shorter than the ∼1 Myr age of the ONC, underscoring the known “proplyd lifetime problem.” Disk masses that are underestimated due to being optically thick remains one explanation to ease this discrepancy.