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Register a new userNon-Keplerian spirals, a gas-pressure dust trap and an eccentric gas cavity in the circumbinary disc around HD 142527
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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.
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The combination of high resolution and sensitivity offered by ALMA is revolutionizing our understanding of protoplanetary discs, as their bulk gas and dust distributions can be studied independently. In this paper we present resolved ALMA observations of the continuum emission ($lambda=1.3$ mm) and CO isotopologues ($^{12}$CO, $^{13}$CO, C$^{18}$O $J=2-1$) integrated intensity from the disc around the nearby ($d = 162$ pc), intermediate mass ($M_{star}=1.67,M_{odot}$) pre-main-sequence star CQ Tau. The data show an inner depression in continuum, and in both $^{13}$CO and C$^{18}$O emission. We employ a thermo-chemical model of the disc reproducing both continuum and gas radial intensity profiles, together with the disc SED. The models show that a gas inner cavity with size between 15 and 25 au is needed to reproduce the data with a density depletion factor between $sim 10^{-1}$ and $sim 10^{-3}$. The radial profile of the distinct cavity in the dust continuum is described by a Gaussian ring centered at $R_{rm dust}=53,$au and with a width of $sigma=13,$au. Three dimensional gas and dust numerical simulations of a disc with an embedded planet at a separation from the central star of $sim20,$au and with a mass of $sim 6textrm{-} 9,M_{rm Jup}$ reproduce qualitatively the gas and dust profiles of the CQ Tau disc. However, a one planet model appears not to be able to reproduce the dust Gaussian density profile predicted using the thermo-chemical modeling.
We test the hypothesis that the disc cavity in the `transition disc Oph IRS 48 is carved by an unseen binary companion. We use 3D dust-gas smoothed-particle hydrodynamics simulations to demonstrate that marginally coupled dust grains concentrate in the gas over-density that forms in in the cavity around a low binary mass ratio binary. This produces high contrast ratio dust asymmetries at the cavity edge similar to those observed in the disc around IRS 48 and other transition discs. This structure was previously assumed to be a vortex. However, we show that the observed velocity map of IRS 48 displays a peculiar asymmetry that is not predicted by the vortex hypothesis. We show the unusual kinematics are naturally explained by the non-Keplerian flow of gas in an eccentric circumbinary cavity. We further show that perturbations observed in the isovelocity curves of IRS 48 may be explained as the product of the dynamical interaction between the companion and the disc. The presence of a $sim$0.4 M$_{odot}$ companion at a $sim$10 au separation can qualitatively explain these observations. High spatial resolution line and continuum imaging should be able to confirm this hypothesis.
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.
We study a warping instability of a geometrically thin, non-self-gravitating, circumbinary disk around young binary stars on an eccentric orbit. Such a disk is subject to both the tidal torques due to a time-dependent binary potential and the radiative torques due to radiation emitted from each star. The tilt angle between the circumbinary disk plane and the binary orbital plane is assumed to be very small. We find that there is a radius within/beyond which the circumbinary disk is unstable to radiation-driven warping, depending on the disk density and temperature gradient indices. This marginally stable warping radius is very sensitive to viscosity parameters, a fiducial disk radius and the temperature measured there, the stellar luminosity, and the disk surface density at a radius where the disk changes from the optically thick to thin for the irradiation from the central stars. On the other hand, it is insensitive to the orbital eccentricity and binary irradiation parameter, which is a function of the binary mass ratio and luminosity of each star. Since the tidal torques can suppress the warping in the inner part of the circumbinary disk, the disk starts to be warped in the outer part. While the circumbinary disks are most likely to be subject to the radiation-driven warping on a AU to kilo-AU scale for binaries with young massive stars more luminous than 10^4Lsun, the radiation driven warping does not work for those around young binaries with the luminosity comparable to the solar luminosity.
The disc around the Herbig Ae/Be star HD 100546 is one of the most extensively studied discs in the southern sky. Although there is a wealth of information about its dust content and composition, not much is known about its gas and large scale kinematics. We detect and study the molecular gas in the disc at spatial resolution from 7.7 to 18.9 using the APEX telescope. The lines 12CO J=7-6, J=6-5, J=3-2, 13CO J=3-2 and [C I] 3P2-3P1 are observed, diagnostic of disc temperature, size, chemistry, and kinematics. We use parametric disc models that reproduce the low-J 12CO emission from Herbig~Ae stars and vary the basic disc parameters - temperature, mass and size. Using the molecular excitation and radiative transfer code RATRAN we fit the observed spectral line profiles. Our observations are consistent with more than 0.001 Msun of molecular gas in a disc of approximately 400 AU radius in Keplerian rotation around a 2.5 Msun star, seen at an inclination of 50 degrees. The detected 12CO lines are dominated by gas at 30-70~K. The non-detection of the [C I] line indicates excess ultraviolet emission above that of a B9 type model stellar atmosphere. Asymmetry in the 12CO line emission suggests that one side of the outer disc is colder by 10-20~K than the other, possibly due to a shadow by a warped geometry of the inner disc. Pointing offsets, foreground cloud absorption and asymmetry in the disc extent are excluded scenarios. Efficient heating of the outer disc ensures that low- and high-J 12CO lines are dominated by the outermost disc regions, indicating a 400 AU radius. The 12CO J=6--5 line arises from a disc layer higher above disc midplane, and warmer by 15-20~K than the layer emitting the J=3--2 line. The existing models of discs around Herbig Ae stars, assuming a B9.5 type model stellar atmosphere overproduce the [CI] 3P2--3P1 line intensity from HD 100546 by an order of magnitude.
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