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Register a new userLinking Outer Disk Pebble Dynamics and Gaps to Inner Disk Water Enrichment
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Millimeter continuum imaging of protoplanetary disks reveals the distribution of solid particles and the presence of substructures (gaps and rings) beyond 5-10 au, while infrared (IR) spectra provide access to abundances of gaseous species at smaller disk radii. Building on recent observational findings of an anti-correlation between the inner disk water luminosity and outer dust disk radius, we aim here at investigating the dynamics of icy solids that drift from the outer disk and sublimate their ice inside the snow line, enriching the water vapor that is observed in the IR. We use a volatile-inclusive disk evolution model to explore a range of conditions (gap location, particle size, disk mass, and alpha-viscosity) under which gaps in the outer disk efficiently block the inward drift of icy solids. We find that inner-disk vapor enrichment is highly sensitive to the location of a disk gap, yielding for each particle size a radial sweet spot that reduces the inner-disk vapor enrichment to a minimum. For pebbles of 1-10 mm in size, which carry the most mass, this sweet spot is at 7-15 au, suggesting that inner gaps may have a key role in reducing ice delivery to the inner disk and may not allow the formation of Earths and super-Earths. This highlights the importance of observationally determining the presence and properties of inner gaps in disks. Finally, we argue that the inner water vapor abundance can be used as a proxy for estimating the pebble drift efficiency and mass-flux entering the inner disk.
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We present Very Large Array observations at 7 mm that trace the thermal emission of large dust grains in the HD 169142 protoplanetary disk. Our images show a ring of enhanced emission of radius ~25-30 AU, whose inner region is devoid of detectable 7 mm emission. We interpret this ring as tracing the rim of an inner cavity or gap, possibly created by a planet or a substellar companion. The ring appears asymmetric, with the western part significantly brighter than the eastern one. This azimuthal asymmetry is reminiscent of the lopsided structures that are expected to be produced as a consequence of trapping of large dust grains. Our observations also reveal an outer annular gap at radii from ~40 to ~70 AU. Unlike other sources, the radii of the inner cavity, the ring, and the outer gap observed in the 7 mm images, which trace preferentially the distribution of large (mm/cm sized) dust grains, coincide with those obtained from a previous near-infrared polarimetric image, which traces scattered light from small (micron- sized) dust grains. We model the broad-band spectral energy distribution and the 7 mm images to constrain the disk physical structure. From this modeling we infer the presence of a small (radius ~0.6 AU) residual disk inside the central cavity, indicating that the HD 169142 disk is a pre-transitional disk. The distribution of dust in three annuli with gaps in between them suggests that the disk in HD 169142 is being disrupted by at least two planets or substellar objects.
Since the discovery of the multi-ring structure of the HL Tau disk, ALMA data suggest that the dust continuum emission of many, if not all, protoplanetary disks consists of rings and gaps, no matter their spectral type or age. The origin of these gaps so far remains unclear. We present a sample study of 16 disks with multiple ring-like structures in the continuum, using published ALMA archival data, to compare their morphologies and gap locations in a systematic way. The 16 targets range from early to late type stars, from <0.5 Myr to >10 Myr, from ~0.2 to 40 L_Sun and include both full and transitional disks with cleared inner dust cavities. Stellar ages are revised using new Gaia distances. Gap locations are derived using a simple radial fit to the intensity profiles. Using a radiative transfer model, the temperature profiles are computed. The gap radii generally do not correspond to the orbital radii of snow lines of the most common molecules. A snow line model can likely be discarded as a common origin of multi-ring systems. In addition, there are no systematic trends in the gap locations that could be related to resonances of planets. Finally, the outer radius of the disks decreases for the oldest disks in the sample, indicating that if multi-ring disks evolve in a similar way, outer dust rings either dissipate with the gas or grow into planetesimal belts.
While planet formation is thought to occur early in the history of a protoplanetary disk, the presence of planets embedded in disks, or of other processes driving disk evolution, might be traced from their imprints on the disk structure. We observed the T Tauri star HD 143006, located in the 5-11 Myr-old Upper Sco region, in polarized scattered light with VLT/SPHERE at near-infrared wavelengths, reaching an angular resolution of ~0.037 (~6 au). We obtained two datasets, one with a 145 mas diameter coronagraph, and the other without, enabling us to probe the disk structure down to an angular separation of ~0.06 (~10 au). In our observations, the disk of HD 143006 is clearly resolved up to ~0.5 and shows a clear large-scale asymmetry with the eastern side brighter than the western side. We detect a number of additional features, including two gaps and a ring. The ring shows an overbrightness at a position angle (PA) of ~140 deg, extending over a range in position angle of ~60 deg, and two narrow dark regions. The two narrow dark lanes and the overall large-scale asymmetry are indicative of shadowing effects, likely due to a misaligned inner disk. We demonstrate the remarkable resemblance between the scattered light image of HD 143006 and a model prediction of a warped disk due to an inclined binary companion. The warped disk model, based on the hydrodynamic simulations combined with 3D radiative transfer calculations, reproduces all major morphological features. However, it does not account for the observed overbrightness at PA~140 deg. Shadows have been detected in several protoplanetary disks, suggesting that misalignment in disks is not uncommon. However, the origin of the misalignment is not clear. As-yet-undetected stellar or massive planetary companions could be responsible for them, and naturally account for the presence of depleted inner cavities.
We used new ALMA $^{13}$CO and C$^{18}$O(3-2) observations obtained at high angular resolution ($sim$0.2) together with previous CO(3-2) and (6-5) ALMA data and continuum maps at 1.3 and 0.8 mm in order to determine the gas properties (temperature, density, and kinematics) in the cavity and to a lesser extent in the outer disk of GG Tau A, the prototype of a young triple T Tauri star that is surrounded by a massive and extended Keplerian outer disk. By deprojecting, we studied the radial and azimuthal gas distribution and its kinematics. We also applied a new method to improve the deconvolution of the CO data and in particular better quantify the emission from gas inside the cavity. We perform local and nonlocal thermodynamic equilibrium studies in order to determine the excitation conditions and relevant physical parameters inside the ring and in the central cavity. Residual emission after removing a smooth-disk model indicates unresolved structures at our angular resolution, probably in the form of irregular rings or spirals. The outer disk is cold, with a temperature $<20$ K beyond 250 au that drops quickly (r$^{-1}$). The kinematics of the gas inside the cavity reveals infall motions at about 10% of the Keplerian speed. We derive the amount of gas in the cavity, and find that the brightest clumps, which contain about 10% of this mass, have kinetic temperatures 40$-$80 K, CO column densities of a few 10$^{17}$ cm$^{-2}$, and H$_2$ densities around 10$^7$ cm$^{-3}$. Although the gas in the cavity is only a small fraction of the disk mass, the mass accretion rate throughout the cavity is comparable to or higher than the stellar accretion rate. It is accordingly sufficient to sustain the circumstellar disks on a long timescale.
Pairs of azimuthal intensity decrements at near symmetric locations have been seen in a number of protoplanetary disks. They are most commonly interpreted as the two shadows cast by a highly misaligned inner disk. Direct evidence of such an inner disk, however, remain largely illusive, except in rare cases. In 2012, a pair of such shadows were discovered in scattered light observations of the near face-on disk around 2MASS J16042165-2130284, a transitional object with a cavity $sim$60 AU in radius. The star itself is a `dipper, with quasi-periodic dimming events on its light curve, commonly hypothesized as caused by extinctions by transiting dusty structures in the inner disk. Here, we report the detection of a gas disk inside the cavity using ALMA observations with $sim0$farcs2 angular resolution. A twisted butterfly pattern is found in the moment 1 map of CO (3-2) emission line towards the center, which is the key signature of a high misalignment between the inner and outer disks. In addition, the counterparts of the shadows are seen in both dust continuum emission and gas emission maps, consistent with these regions being cooler than their surroundings. Our findings strongly support the hypothesized misaligned-inner-disk origin of the shadows in the J1604-2130 disk. Finally, the inclination of inner disk would be close to -45 $^{circ}$ in contrast with 45 $^{circ}$; it is possible that its internal asymmetric structures cause the variations on the light curve of the host star.
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