Abstract 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, 12 CO) and near-infrared (Spectro-polarimetric High-contrast Exoplanet Research; 1.5–2.5 μ m) 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 μ m) and L ′ (3.7 μ m) 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 5 σ 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 (<0.″5) resolved in both CO and polarimetric 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.
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Detection of Near-infrared Water Ice at the Surface of the (Pre)Transitional Disk of AB Aur: Informing Icy Grain Abundance, Composition, and Size
Abstract We present near-infrared Large Binocular Telescope LMIRCam imagery of the disk around the Herbig Ae/Be star AB Aurigae. A comparison of the surface brightness at K s (2.16 μ m), H 2 O narrowband (3.08 μ m), and L ′ (3.7 μ m) allows us to probe the presence of icy grains in this (pre)transitional disk environment. By applying reference differential imaging point-spread function subtraction, we detect the disk at high signal-to-noise ratios in all three bands. We find strong morphological differences between the bands, including asymmetries consistent with the observed spiral arms within 100 au in L ′ . An apparent deficit of scattered light at 3.08 μ m relative to the bracketing wavelengths ( K s and L ′ ) is evocative of ice absorption at the disk surface layer. However, the Δ( K s − H 2 O) color is consistent with grains with little to no ice (0%–5% by mass). The Δ ( H 2 O − L ′ ) color, conversely, suggests grains with a much higher ice mass fraction (∼0.68), and the two colors cannot be reconciled under a single grain population model. Additionally, we find that the extremely red Δ ( K s − L ′ ) disk color cannot be reproduced under conventional scattered light modeling with any combination of grain parameters or reasonable local extinction values. We hypothesize that the scattering surfaces at the three wavelengths are not colocated, and that the optical depth effects in each wavelength result from probing the grain population at different disk surface depths. The morphological similarity between K s and H 2 O suggests that their scattering surfaces are near one another, lending credence to the Δ( K s − H 2 O) disk color constraint of <5% ice mass fraction for the outermost scattering disk layer.
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- Award ID(s):
- 2009816
- NSF-PAR ID:
- 10352982
- Date Published:
- Journal Name:
- The Astronomical Journal
- Volume:
- 163
- Issue:
- 4
- ISSN:
- 0004-6256
- Page Range / eLocation ID:
- 145
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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- Free Publicly Accessible Full Text
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Accepted Manuscript1.0
- Journal Article:
- https://doi.org/10.3847/1538-3881/ac4d9b
