Search

Multiwavelength high-resolution imaging of protoplanetary disks has revealed the presence of multiple, varied substructures in their dust and gas components, which might be signposts of young, forming planetary systems. AB Aurigae bears an emblematic (pre)transitional disk showing spiral structures observed in the inner cavity of the disk in both the submillimeter (Atacama Large Millimeter/submillimeter Array (ALMA); 1.3 mm, 12CO) and near-infrared (Spectro-polarimetric High-contrast Exoplanet Research; 1.5–2.5 μm) wavelengths, which have been claimed to arise from dynamical interactions with a massive companion. In this work, we present new deep K s (2.16 μm) and L′ (3.7 μm) band images of AB Aurigae obtained with the L/M-band Infrared Camera on the Large Binocular Telescope, aimed for the detection of both planetary companions and extended disk structures. No point source is recovered, in particular at the outer regions of the disk, where a putative candidate (ρ = 0.″681, PA = 7.°6) had been previously claimed. The nature of a second innermost planet candidate (ρ = 0.″16, PA = 203.°9) cannot be investigated by the new data. We are able to derive 5σ detection limits in both magnitude and mass for the system, going from 14 M Jup at 0.″3 (49 au) down to 3–4 M Jup at 0.″6 (98 au) and beyond, based on the ATMO 2020 evolutionary models. We detect the inner spiral structures (H-band observations. We also recover the ring structure of the system at larger separation (0.″5–0.″7) showing a clear southeast/northwest asymmetry. This structure, observed for the first time at L′ band, remains interior to the dust cavity seen at ALMA, suggesting an efficient dust trapping mechanism at play in the disk.

Direct imaging of exoplanets requires both high contrast and high spatial resolution. Here, we present the first scientific results obtained with the newly commissioned apodizing phase plate coronagraph (APP) on VLT/NACO. We detected the exoplanet β Pictoris b in the narrowband filter centered at 4.05 μm (NB4.05). The position angle (20913 ± 212) and the projected separation to its host star (0354 ± 0012, i.e., 6.8 ± 0.2 AU at a distance of 19.3 pc) are in good agreement with the recently presented data from Lagrange et al. Comparing the observed NB4.05 magnitude of 11.20 ± 0.23 mag to theoretical atmospheric models, we find a best fit with a 7-10 M Jupiter object for an age of 12 Myr, again in agreement with previous estimates. Combining our results with published L' photometry, we can compare the planet's [L' – NB4.05] color to that of cool field dwarfs of higher surface gravity suggesting an effective temperature of ~1700 K. The best-fit theoretical model predicts an effective temperature of ~1470 K, but this difference is not significant given our photometric uncertainties. Our results demonstrate the potential of NACO/APP for future planet searches and provide independent confirmation as well as complementary data for β Pic b.

We developed a simple, physical and self-consistent cloud model for brown dwarfs and young giant exoplanets. We compared different parametrisations for the cloud particle size, by either fixing particle radii, or fixing the mixing efficiency (parameter fsed) or estimating particle radii from simple microphysics. The cloud scheme with simple microphysics appears as the best parametrisation by successfully reproducing the observed photometry and spectra of brown dwarfs and young giant exoplanets. In particular, it reproduces the L-T transition, due to the condensation of silicate and iron clouds below the visible/near-IR photosphere. It also reproduces the reddening observed for low-gravity objects, due to an increase of cloud optical depth for low gravity. In addition, we found that the cloud greenhouse effect shifts chemical equilibriums, increasing the abundances of species stable at high temperature. This effect should significantly contribute to the strong variation of methane abundance at the L-T transition and to the methane depletion observed on young exoplanets. Finally, we predict the existence of a continuum of brown dwarfs and exoplanets for absolute J magnitude=15-18 and J-K color=0-3, due to the evolution of the L-T transition with gravity. This self-consistent model therefore provides a general framework to understand the effects of clouds and appears well-suited for atmospheric retrievals., 24 pages, 20 figures, submitted to ApJ. Comments welcome