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Register a new userSignificant Gas-to-Dust Ratio Asymmetry and Variation in the Disk of HD 142527 and the Indication of Gas Depletion
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We investigate the dust and gas distribution in the disk around HD 142527 based on ALMA observations of dust continuum, 13CO(3-2), and C18O(3-2) emission. The disk shows strong azimuthal asymmetry in the dust continuum emission, while gas emission is more symmetric. In this paper, we investigate how gas and dust are distributed in the dust-bright northern part of the disk and in the dust-faint southern part. We construct two axisymmetric disk models. One reproduces the radial profiles of the continuum and the velocity moments 0 and 1 of CO lines in the north and the other reproduces those in the south. We have found that the dust is concentrated in a narrow ring having ~50AU width (in FWHM; w_d=30AU in our parameter definition) located at ~170-200AU from the central star. The dust particles are strongly concentrated in the north. We have found that the dust surface density contrast between the north and south amounts to ~70. Compared to the dust, the gas distribution is more extended in the radial direction. We find that the gas component extends at least from ~100AU to ~250AU from the central star, and there should also be tenuous gas remaining inside and outside of these radii. The azimuthal asymmetry of gas distribution is much smaller than dust. The gas surface density differs only by a factor of ~3-10 between the north and south. Hence, gas-to-dust ratio strongly depends on the location of the disk: ~30 at the location of the peak of dust distribution in the south and ~3 at the location of the peak of dust distribution in the north. Despite large uncertainties, the overall gas-to-dust ratio is inferred to be ~10-30, indicating that the gas depletion may have already been under way.
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We present ALMA observations of the $98.5~mathrm{GHz}$ dust continuum and the $mathrm{^{13}CO}~J = 1 - 0$ and $mathrm{C^{18}O}~J = 1 - 0$ line emissions of the protoplanetary disk associated with HD~142527. The $98.5~mathrm{GHz}$ continuum shows a strong azimuthal-asymmetric distribution similar to that of the previously reported $336~mathrm{GHz}$ continuum, with a peak emission in dust concentrated region in the north. The disk is optically thin in both the $98.5~mathrm{GHz}$ dust continuum and the $mathrm{C^{18}O}~J = 1 - 0$ emissions. We derive the distributions of gas and dust surface densities, $Sigma_mathrm{g}$ and $Sigma_mathrm{d}$, and the dust spectral opacity index, $beta$, in the disk from ALMA Band 3 and Band 7 data. In the analyses, we assume the local thermodynamic equilibrium and the disk temperature to be equal to the peak brightness temperature of $mathrm{^{13}CO}~J = 3 - 2$ with a continuum emission. The gas-to-dust ratio, $mathrm{G/D}$, varies azimuthally with a relation $mathrm{G/D} propto Sigma_mathrm{d}^{-0.53}$, and $beta$ is derived to be $approx 1$ and $approx 1.7$ in the northern and southern regions of the disk, respectively. These results are consistent with the accumulation of larger dust grains in a higher pressure region. In addition, our results show that the peak $Sigma_mathrm{d}$ is located ahead of the peak $Sigma_mathrm{g}$. If the latter corresponds to a vortex of high gas pressure, the results indicate that the dust is trapped ahead of the vortex, as predicted by some theoretical studies.
The amount of dust present in circumstellar disks is expected to steadily decrease with age due to the growth from micron-sized particles to planetesimals and planets. Mature circumstellar disks, however, can be observed to contain significant amounts of dust and possess high dust-to-gas ratios. Using HD 163296 as our case study, we explore how the formation of giant planets in disks can create the conditions for collisionally rejuvenating the dust population, halting or reversing the expected trend. We combine N-body simulations with statistical methods and impact scaling laws to estimate the dynamical and collisional excitation of the planetesimals due to the formation of HD 163296s giant planets. We show that this process creates a violent collisional environment across the disk that can inject collisionally produced second-generation dust into it, significantly contributing to the observed dust-to-gas ratio. The spatial distribution of the dust production can explain the observed local enrichments in HD 163296s inner regions. The results obtained for HD 163296 can be extended to any disk with embedded forming giant planets and may indicate a common evolutionary stage in the life of such circumstellar disks. Furthermore, the dynamical excitation of the planetesimals could result in the release of transient, non-equilibrium gas species like H2O, CO2, NH3 and CO in the disk due to ice sublimation during impacts and, due to the excited planetesimals being supersonic with respect to the gas, could produce bow shocks in the latter that could heat it and cause a broadening of its emission lines.
We present ALMA observations of the $^{12}$CO, $^{13}$CO, C$^{18}$O J=2-1 transitions and the 1.3,mm continuum emission for the circumbinary disc around HD 142527, at an angular resolution of $approx$,0farcs3. We observe multiple spiral structures in intensity, velocity and velocity dispersion for the $^{12}$CO and $^{13}$CO gas tracers. A newly detected $^{12}$CO spiral originates from the dust horseshoe, and is rotating at super-Keplerian velocity or vertically ascending, whilst the inter-spiral gas is rotating at sub-Keplerian velocities. This new spiral possibly connects to a previously identified spiral, thus spanning > 360$^circ$. A spatial offset of ~30 au is observed between the $^{12}$CO and $^{13}$CO spirals, to which we hypothesize that the gas layers are propagating at different speeds (``surfing) due to a non-zero vertical temperature gradient. Leveraging the varying optical depths between the CO isotopologues, we reconstruct temperature and column density maps of the outer disc. Gas surface density peaks at r,$approx$,180,au, coincident with the peak of continuum emission. Here the dust grains have a Stokes number of $approx$,1, confirming radial and azimuthal trapping in the horseshoe. We measure a cavity radius at half-maximum surface density of $approx$,100,au, and a cavity eccentricity between 0.3 and 0.45.
HD$,$169142 is an excellent target to investigate signs of planet-disk interaction due to the previous evidence of gap structures. We performed J-band (~1.2{mu}m) polarized intensity imaging of HD169142 with VLT/SPHERE. We observe polarized scattered light down to 0.16 (~19 au) and find an inner gap with a significantly reduced scattered light flux. We confirm the previously detected double ring structure peaking at 0.18 (~21 au) and 0.56 (~66 au), and marginally detect a faint third gap at 0.70-0.73 (~82-85 au). We explore dust evolution models in a disk perturbed by two giant planets, as well as models with a parameterized dust size distribution. The dust evolution model is able to reproduce the ring locations and gap widths in polarized intensity, but fails to reproduce their depths. It, however, gives a good match with the ALMA dust continuum image at 1.3 mm. Models with a parameterized dust size distribution better reproduce the gap depth in scattered light, suggesting that dust filtration at the outer edges of the gaps is less effective. The pile-up of millimeter grains in a dust trap and the continuous distribution of small grains throughout the gap likely require a more efficient dust fragmentation and dust diffusion in the dust trap. Alternatively, turbulence or charging effects might lead to a reservoir of small grains at the surface layer that is not affected by the dust growth and fragmentation cycle dominating the dense disk midplane. The exploration of models shows that extracting planet properties such as mass from observed gap profiles is highly degenerate.
We present far-IR/sub-mm imaging and spectroscopy of 49 Ceti, an unusual circumstellar disk around a nearby young A1V star. The system is famous for showing the dust properties of a debris disk, but the gas properties of a low-mass protoplanetary disk. The data were acquired with the Herschel Space Observatory PACS and SPIRE instruments, largely as part of the Gas in Protoplanetary Systems (GASPS) Open Time Key Programme. Disk dust emission is detected in images at 70, 160, 250, 350, and 500 mu m; 49 Cet is significantly extended in the 70 mu m image, spatially resolving the outer dust disk for the first time. Spectra covering small wavelength ranges centered on eight atomic and molecular emission lines were obtained, including [OI] 63 mu m and [CII] 158 mu m. The CII line was detected at the 5sigma level - the first detection of atomic emission from the disk. No other emission lines were seen, despite the fact that the OI line is the brightest one observed in Herschel protoplanetary disk spectra (Meeus et al. 2012; Dent et al. 2013). We present an estimate of the amount of circumstellar atomic gas implied by the CII emission. The new far-IR/sub-mm data fills in a large gap in the previous spectral energy distribution (SED) of 49 Cet. A simple model of the new SED confirms the two-component structure of the disk: warm inner dust and cold outer dust that produces most of the observed excess. Finally, we discuss preliminary thermochemical modeling of the 49 Cet gas/dust disk and our attempts to match several observational results simultaneously. Although we are not yet successful in doing so, our investigations shed light on the evolutionary status of the 49 Cet gas, which might not be primordial gas but rather secondary gas coming from comets.
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