Pablo E. Román

Flows of gas through a protoplanetary gap.

The formation of gaseous giant planets is thought to occur in the first few million years after stellar birth. Models predict that the process produces a deep gap in the dust component (shallower in the gas). Infrared observations of the disk around the young star HD 142527 (at a distance of about 140 parsecs from Earth) found an inner disk about 10 astronomical units (au) in radius (1 au is the Earth–Sun distance), surrounded by a particularly large gap and a disrupted outer disk beyond 140 au. This disruption is indicative of a perturbing planetary-mass body at about 90 au. Radio observations indicate that the bulk mass is molecular and lies in the outer disk, whose continuum emission has a horseshoe morphology. The high stellar accretion rate would deplete the inner disk in less than one year, and to sustain the observed accretion matter must therefore flow from the outer disk and cross the gap. In dynamical models, the putative protoplanets channel outer-disk material into gap-crossing bridges that feed stellar accretion through the inner disk. Here we report observations of diffuse CO gas inside the gap, with denser HCO+ gas along gap-crossing filaments. The estimated flow rate of the gas is in the range of 7 × 10−9 to 2 × 10−7 solar masses per year, which is sufficient to maintain accretion onto the star at the present rate.1. Departamento de Astronomı́a, Universidad de Chile, Casilla 36-D, Santiago, Chile 2. Joint ALMA Observatory, Alonso de Córdova 3107, Vitacura 763-0355, Santiago Chile 3. European Southern Observatory (ESO), Casilla 19001, Vitacura, Santiago, Chile 4. National Radio Astronomy Observatory, 520 Edgemont Road, Charlottesville, VA 22903-2475, USA 5. Observatoire de Genève, Université de Genève, 51 ch. des Maillettes, 1290, Versoix, Switzerland 6. Departamento de Astronomı́a y Astrofı́sica, Pontificia Universidad Católica de Chile, Santiago, Chile 7. UMI-FCA, CNRS / INSU France (UMI 3386) , and Departamento de Astronomı́a, Universidad de Chile, Santiago, Chile. 8. CNRS / UJF Grenoble 1, UMR 5274, Institut de Planétologie et dAstrophysique de Grenoble (IPAG), France 9. Harvard-Smithsonian Center for Astrophysics, 60 Garden Street, Cambridge, MA 02138 USA 10. Department of Astronomy, U. C. Berkeley, 601 Campbell Hall, Berkeley, CA 94720 11. Departamento de Fı́sica y Astronomı́a, Universidad Valparaiso, Av. Gran Bretana 111, Valparaiso, Chile. 12. University Observatory, Ludwig-Maximillians University, Munich.

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.

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)

Web User Session Reconstruction Using Integer Programming

An important input for Web usage mining is Web user sessions that must be reconstructed from Web logs (sessionization) when such sessions are not otherwise identified. We present a novel approach for sessionization based on an integer program. We compare results of our approach with the timeout heuristic on Web logs from an academic Web site. We find our integer program provides sessions that better match an expected empirical distribution with about half of the standard error of the heuristic.

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.

GAS INSIDE the 97 AU CAVITY AROUND the TRANSITION DISK Sz 91

We present ALMA (Cycle 0) band-6 and band-3 observations of the transition disk Sz\,91. The disk inclination and position angle are determined to be

Predicting web user behavior using learning-based ant colony optimization

i=49.5\degr\pm3.5\degr

Planet Formation Signposts: Observability of Circumplanetary Disks Via Gas Kinematics

and

A Dynamic Stochastic Model Applied to the Analysis of the Web User Behavior

\mathrm{PA}=18.2\degr\pm3.5\degr