Sebastian Perez

SHADOWS CAST BY A WARP IN THE HD 142527 PROTOPLANETARY DISK

Detailed observations of gaps in protoplanetary disks have revealed structures that drive current research on circumstellar disks. One such feature is the two intensity nulls seen along the outer disk of the HD 142527 system, which are particularly well traced in polarized differential imaging. Here we propose that these are shadows cast by the inner disk. The inner and outer disk are thick, in terms of the unit-opacity surface in H-band, so that the shape and orientation of the shadows inform on the three-dimmensional structure of the system. Radiative transfer predictions on a parametric disk model allow us to conclude that the relative inclination between the inner and outer disks is 70+-5 deg. This finding taps the potential of high-contrast imaging of circumstellar disks, and bears consequences on the gas dynamics of gapped disks, as well as on the physical conditions in the shadowed regions.

CO Gas Inside the Protoplanetary Disk Cavity in HD 142527: Disk Structure from ALMA

Inner cavities and annular gaps in circumstellar disks are possible signposts of giant planet formation. The young star HD 142527 hosts a massive protoplanetary disk with a large cavity that extends up to 140 AU from the central star, as seen in continuum images at infrared and millimeter wavelengths. Estimates of the survival of gas inside disk cavities are needed to discriminate between clearing scenarios. We present a spatially and spectrally resolved carbon monoxide isotopologue observations of the gas-rich disk HD 142527, in the J = 2-1 line of 12CO, 13CO, and C18O obtained with the Atacama Large Millimeter/submillimeter Array (ALMA). We detect emission coming from inside the dust-depleted cavity in all three isotopologues. Based on our analysis of the gas in the dust cavity, the 12CO emission is optically thick, while 13CO and C18O emissions are both optically thin. The total mass of residual gas inside the cavity is ~1.5-2 M Jup. We model the gas with an axisymmetric disk model. Our best-fit model shows that the cavity radius is much smaller in CO than it is in millimeter continuum and scattered light observations, with a gas cavity that does not extend beyond 105 AU (at 3?). The gap wall at its outer edge is diffuse and smooth in the gas distribution, while in dust continuum it is manifestly sharper. The inclination angle, as estimated from the high velocity channel maps, is 28 ? 0.5?deg, higher than in previous estimates, assuming a fix central star mass of 2.2 M ?.

ACCRETION KINEMATICS THROUGH THE WARPED TRANSITION DISK IN HD 142527 FROM RESOLVED CO(6–5) OBSERVATIONS

The finding of residual gas in the large central cavity of the HD 142527 disk motivates questions regarding the origin of its non-Keplerian kinematics and possible connections with planet formation. We aim to understand the physical structure that underlies the intra-cavity gaseous flows, guided by new molecular-line data in CO(6–5) with unprecedented angular resolutions. Given the warped structure inferred from the identification of scattered-light shadows cast on the outer disk, the kinematics are consistent, to first order, with axisymmetric accretion onto the inner disk occurring at all azimuths. A steady-state accretion profile, fixed at the stellar accretion rate, explains the depth of the cavity as traced in CO isotopologues. The abrupt warp and evidence for near free-fall radial flows in HD 142527 resemble theoretical models for disk tearing, which could be driven by the reported low-mass companion, whose orbit may be contained in the plane of the inner disk. The companion’s high inclination with respect to the massive outer disk could drive Kozai oscillations over long timescales; high-eccentricity periods may perhaps account for the large cavity. While shadowing by the tilted disk could imprint an azimuthal modulation in the molecular-line maps, further observations are required to ascertain the significance of azimuthal structure in the density field inside the cavity of HD 142527.

Spiral arms in the disk of HD 142527 from CO emission lines with ALMA

In view of both the size of its gap and the previously reported asymmetries and near-infrared spiral arms, the transition disk of the Herbig Fe star HD 142527 constitutes a remarkable case study. This paper focuses on the morphology of the outer disk through ALMA observations of 12CO J = 2-1, 12CO J = 3-2, and 13CO J = 2-1. Both 12CO J = 2-1 and 12CO J = 3-2 show spiral features of different sizes. The innermost spiral arm (S1) is a radio counterpart of the first near-infrared spiral observed by Fukagawa, but it is shifted radially outward. However, the most conspicuous CO spiral arm (S2) lies at the outskirts of the disk and has not been detected before. It corresponds to a cold density structure, with both brightness and excitation temperatures of order 13±2 K and conspicuous in the 12CO J = 2-1 peak-intensity map, but faint in 12CO J = 3-2. There is also a faint counterarm (S3), at a point-symmetric location of S2 with respect to the star. These three spirals are modeled separately with two different formulae that approximate the loci of density maxima in acoustic waves due to embedded planets. S1 could be fit relatively well with these formulae, compared to S2 and S3. Alternative scenarios such as gravitational instability or external tidal interaction are discussed. The impact of channelization on spectrally and spatially resolved peak intensity maps is also briefly addressed.

Exocometary gas in the HD 181327 debris ring

ALMA is a partnership of ESO (representing its member states), NSF (USA) and NINS (Japan), together with NRC (Canada) and NSC and ASIAA (Taiwan) and KASI (Republic of Korea), in cooperation with the Republic of Chile. The Joint ALMA Observatory is operated by ESO, AUI/NRAO and NAOJ. This work was supported by the European Union through ERC grant number 279973. SM, SC, SP acknowledge financial support from Millennium Nucleus RC130007 (Chilean Ministry of Economy), and additionally by FONDECYT grants 1130949 and 3140601. GMK is supported by the Royal Society as a Royal Society University Research Fellow.

A COMPACT CONCENTRATION OF LARGE GRAINS IN THE HD 142527 PROTOPLANETARY DUST TRAP

A pathway to the formation of planetesimals, and eventually giant planets, may occur in concentrations of dust grains trapped in pressure maxima. Dramatic crescent-shaped dust concentrations have been seen in recent radio images at sub-mm wavelengths. These disk asymmetries could represent the initial phases of planet formation in the dust trap scenario, provided that grain sizes are spatially segregated. A testable prediction of azimuthal dust trapping is that progressively larger grains should be more sharply conned and furthermore the trapped grains should follow a distribution that is markedly dierent from the gas. However, gas tracers such as CO and the infrared emission from small grains are both very optically thick where the submm continuum originates, so observations have been unable to test the trapping predictions or to identify compact concentrations of larger grains required for planet formation by core-accretion. Here we report multifrequency observations of HD 142527, from 34 GHz to 700 GHz, that reveal a compact concentration of cm-sized grains, with a few Earth masses, embedded in a large-scale crescent of mm-sized particles. The emission peaks at wavelengths shorter than 1 mm are optically thick and trace the temperature structure resulting from shadows cast by the inner regions. Given this temperature structure, we infer that the largest dust grains are concentrated in the 34 GHz clump. We conclude that dust trapping is ecient for approximately cm-sized grains and leads to enhanced concentrations, while the smaller grains largely reect the gas distribution. Subject headings: Protoplanetary disks | Planet-disk interactions | Stars: individual: (HD 142527)

Cavity and other radial substructures in the disk around HD 97048

Context. Gaps, cavities, and rings in circumstellar disks are signposts of disk evolution and planet-disk interactions. We follow the recent suggestion that Herbig Ae/Be disks with a flared disk harbor a cavity, and investigate the disk around HD 97048. Aims. We aim to resolve the 34 ± 4 AU central cavity that has been predicted and to investigate the structure of the disk. Methods. We imaged the disk around HD 97048 using ALMA at 0.85 mm and 2.94 mm and ATCA (multiple frequency) observations. Our observations also include the 12 CO J = 1−0, 12 CO J = 3−2 and HCO + J = 4−3 emission lines. Results. A central cavity in the disk around HD 97048 is resolved with a 40−46 AU radius. Additional radial structure present in the surface brightness profile can be accounted for either by an opacity gap at 90 AU or by an additional emitting ring at 150 AU. The continuum emission tracing the dust in the disk is detected out to 355 AU. The 12 CO J = 3−2 disk is detected 2.4 times farther out. The 12 CO emission can be traced down to ≈10 AU scales. Apparent non-Keplerian kinematics are detected inside the cavity on the HCO + J = 4−3 velocity map. The mm spectral index measured from ATCA observations suggests that grain growth has occurred in the HD 97048 disk. Finally, we resolve a highly inclined disk out to 150 AU around the nearby 0.5 M ⊙ binary ISO-ChaI 126. Conclusions. The data presented here reveal a cavity in the disk of HD 97048, and prominent radial structure in the surface brightness. The cavity size varies for different continuum frequencies and gas tracers. The gas inside the cavity follows non-Keplerian kinematics seen in HCO + emission. The variable cavity size along with the kinematical signature suggests the presence of a substellar companion or a massive planet inside the cavity.

COMPACT DUST CONCENTRATION IN THE MWC 758 PROTOPLANETARY DISK

The formation of planetesimals requires that primordial dust grains grow from micron- to km-sized bodies. Dust traps caused by gas pressure maxima have been proposed as regions where grains can concentrate and grow fast enough to form planetesimals, before radially migrating onto the star. We report new VLA Ka & Ku observations of the protoplanetary disk around the Herbig Ae/Be star MWC 758. The Ka image shows a compact emission region in the outer disk indicating a strong concentration of big dust grains. Tracing smaller grains, archival ALMA data in band 7 continuum shows extended disk emission with an intensity maximum to the north-west of the central star, which matches the VLA clump position. The compactness of the Ka emission is expected in the context of dust trapping, as big grains are trapped more easily than smaller grains in gas pressure maxima. We develop a non-axisymmetric parametric model inspired by a steady state vortex solution with parameters adequately selected to reproduce the observations, including the spectral energy distribution. Finally, we compare the radio continuum with SPHERE scattered light data. The ALMA continuum spatially coincides with a spiral-like feature seen in scattered light, while the VLA clump is offset from the scattered light maximum. Moreover, the ALMA map shows a decrement that matches a region devoid of scattered polarised emission. Continuum observations at a different wavelength are necessary to conclude if the VLA-ALMA difference is an opacity or a real dust segregation.

SPARSE APERTURE MASKING OBSERVATIONS OF THE FL Cha PRE-TRANSITIONAL DISK

We present deep Sparse Aperture Masking (SAM) observations obtained with the ESO Very Large Telescope of the pre-transitional disk object FL Cha (SpT = K8, d = 160 pc), the disk of which is known to have a wide optically thin gap separating optically thick inner and outer disk components. We find non-zero closure phases, indicating a significant flux asymmetry in the KS -band emission (e.g., a departure from a single point source detection). We also present radiative transfer modeling of the spectral energy distribution of the FL Cha system and find that the gap extends from 0.06+0.05 – 0.01 AU to 8.3 ± 1.3 AU. We demonstrate that the non-zero closure phases can be explained almost equally well by starlight scattered off the inner edge of the outer disk or by a (sub)stellar companion. Single-epoch, single-wavelength SAM observations of transitional disks with large cavities that could become resolved should thus be interpreted with caution, taking the disk and its properties into consideration. In the context of a binary model, the signal is most consistent with a high-contrast (ΔKS ~ 4.8 mag) source at a ~40 mas (6 AU) projected separation. However, the flux ratio and separation parameters remain highly degenerate and a much brighter source (ΔKS ~ 1 mag) at 15 mas (2.4 AU) can also reproduce the signal. Second-epoch, multi-wavelength observations are needed to establish the nature of the SAM detection in FL Cha.

Planet Formation Signposts: Observability of Circumplanetary Disks Via Gas Kinematics

The identification of on-going planet formation requires the finest angular resolutions and deepest sensitivities in observations inspired by state-of-the-art numerical simulations. Hydrodynamic simulations of planet-disk interactions predict the formation of circumplanetary disks (CPDs) around accreting planetary cores. These CPDs have eluded unequivocal detection -their identification requires predictions in CPD tracers. In this work, we aim to assess the observability of embedded CPDs with ALMA as features imprinted in the gas kinematics. We use 3D Smooth Particle Hydrodynamic (SPH) simulations of CPDs around 1 and 5 M_Jup planets at large stellocentric radii, in locally isothermal and adiabatic disks. The simulations are then connected with 3D radiative transfer for predictions in CO isotopologues. Observability is assessed by corrupting with realistic long baseline phase noise extracted from the recent HL Tau ALMA data. We find that the presence of a CPD produces distinct signposts: 1) compact emission separated in velocity from the overall circumstellar disks Keplerian pattern, 2) a strong impact on the velocity pattern when the Doppler shifted line emission sweeps across the CPD location, and 3) a local increase in the velocity dispersion. We test our predictions with a simulation tailored for HD 100546 -which has a reported protoplanet candidate. We find that the CPDs are detectable in all 3 signposts with ALMA Cycle 3 capabilities for both 1 and 5 M_Jup protoplanets, when embedded in an isothermal disk.