Context. The presence or absence of ice in protoplanetary disks is of great importance to the formation of planets. By enhancing solid surface density and increasing sticking efficiency, ice catalyzes the rapid formation of planetesimals and decreases the timescale of giant planet core accretion. Aims. In this paper, we analyze the composition of the outer disk around the Herbig star HD 142527. We focus on the composition of water ice, but also analyze the abundances of previously proposed minerals. Methods. We present new Herschel far-infrared spectra and a re-reduction of archival data from the Infrared Space Observatory (ISO). We modeled the disk using full 3D radiative transfer to obtain the disk structure. Also, we used an optically thin analysis of the outer disk spectrum to obtain firm constraints on the composition of the dust component. Results. The water ice in the disk around HD 142527 contains a large reservoir of crystalline water ice. We determine the local abundance of water ice in the outer disk (i.e., beyond 130AU). The re-reduced ISO spectrum differs significantly from that previously published, but matches the new Herschel spectrum at their common wavelength range. In particular, we do not detect any significant contribution from carbonates or hydrous silicates, in contrast to earlier claims. Conclusions. The amount of water ice detected in the outer disk requires similar to 80% of oxygen atoms. This is comparable to the water ice abundance in the outer solar system, comets, and dense interstellar clouds. The water ice is highly crystalline while the temperatures where we detect it are too low to crystallize the water on relevant timescales. We discuss the implications of this finding.

Context. Debris discs are a consequence of the planet formation process and constitute the fingerprints of planetesimal systems. Their counterparts in the solar system are the asteroid and Edgeworth-Kuiper belts. Aims. The aim of this paper is to provide robust numbers for the incidence of debris discs around FGK stars in the solar neighbourhood. Methods. The full sample of 177 FGK stars with d <= 20 pc proposed for the DUst around Nearby Stars (DUNES) survey is presented. Herschel/PACS observations at 100 and 160 mu m were obtained, and were complemented in some cases with data at 70 mu m and at 250, 350, and 500 mu m SPIRE photometry. The 123 objects observed by the DUNES collaboration were presented in a previous paper. The remaining 54 stars, shared with the Disc Emission via a Bias-free Reconnaissance in IR and Sub-mm (DEBRIS) consortium and observed by them, and the combined full sample are studied in this paper. The incidence of debris discs per spectral type is analysed and put into context together with other parameters of the sample, like metallicity, rotation and activity, and age. Results. The subsample of 105 stars with d <= 15 pc containing 23 F, 33 G, and 49 K stars is complete for F stars, almost complete for G stars, and contains a substantial number of K stars from which we draw solid conclusions on objects of this spectral type. The incidence rates of debris discs per spectral type are 0.26(-0.14)(+0.21) (6 objects with excesses out of 23 F stars), 0.21(-0.11)(+0.17) (7 out of 33 G stars), and 0.20(-0.09)(+0.14) (10 out of 49 K stars); the fraction for all three spectral types together is 0.22(-0.07)(+0.08) (23 out of 105 stars). The uncertainties correspond to a 95% confidence level. The medians of the upper limits of L-dust/L-* for each spectral type are 7.8 x 10(-7) (F), 1.4 x 10(-6) (G), and 2.2 x 10(-6) (K); the lowest values are around 4.0 x 10(-7). The incidence of debris discs is similar for active (young) and inactive (old) stars. The fractional luminosity tends to drop with increasing age, as expected from collisional erosion of the debris belts.

Using Keck/HIRES spectra (Delta v similar to 7 km s(-1)) we analyze forbidden lines of [O I] 6300 angstrom, [O I] 5577 angstrom. and [S II] 6731 angstrom. from 33 T Tauri stars covering a range of disk evolutionary stages. After removing a high-velocity component (HVC) associated with microjets, we study the properties of the low-velocity component (LVC). The LVC can be attributed to slow disk winds that could be magnetically (magnetohydrodynamic) or thermally (photoevaporative) driven. Both of these winds play an important role in the evolution and dispersal of protoplanetary material. LVC emission is seen in all 30 stars with detected [O. I] but only in two out of eight with detected [S. II], so our analysis is largely based on the properties of the [O. I] LVC. The LVC itself is resolved into broad (BC) and narrow (NC) kinematic components. Both components are found over a wide range of accretion rates and their luminosity is correlated with the accretion luminosity, but the NC is proportionately stronger than the BC in transition disks. The full width at half maximum of both the BC and NC correlates with disk inclination, consistent with Keplerian broadening from radii of 0.05 to 0.5 au and 0.5 to 5 au, respectively. The velocity centroids of the BC suggest formation in an MHD disk wind, with the largest blueshifts found in sources with closer to face-on orientations. The velocity centroids of the NC, however, show no dependence on disk inclination. The origin of this component is less clear and the evidence for photoevaporation is not conclusive.

We develop a simple model to predict the radial distribution of planetesimal formation. The model is based on the observed growth of dust to millimeter-sized particles, which drift radially, pile-up, and form planetesimals where the stopping time and dust-to-gas ratio intersect the allowed region for streaming instability-induced gravitational collapse. Using an approximate analytic treatment, we first show that drifting particles define a track in metallicity-stopping time space whose only substantial dependence is on the disk's angular momentum transport efficiency. Prompt planetesimal formation is feasible for high particle accretion rates (relative to the gas, (M) over dot(p)/(M) over dot greater than or similar to 3 x 10(-2) for alpha = 10(-2)), which could only be sustained for a limited period of time. If it is possible, it would lead to the deposition of a broad and massive belt of planetesimals with a sharp outer edge. Numerically including turbulent diffusion and vapor condensation processes, we find that a modest enhancement of solids near the snow line occurs for centimeter-sized particles, but that this is largely immaterial for planetesimal formation. We note that radial drift couples planetesimal formation across radii in the disk, and suggest that considerations of planetesimal formation favor a model in which the initial deposition of material for giant planet cores occurs well beyond the snow line.

Context. High-contrast scattered light observations have revealed the surface morphology of several dozen protoplanetary disks at optical and near-infrared wavelengths. Inclined disks offer the opportunity to measure part of the phase function of the dust grains that reside in the disk surface which is essential for our understanding of protoplanetary dust properties and the early stages of planet formation. Aims. We aim to construct a method which takes into account how the flaring shape of the scattering surface of an optically thick protoplanetary disk projects onto the image plane of the observer. This allows us to map physical quantities (e.g., scattering radius and scattering angle) onto scattered light images and retrieve stellar irradiation corrected images (r(2)-scaled) and dust phase functions. Methods. The scattered light mapping method projects a power law shaped disk surface onto the detector plane after which the observed scattered light image is interpolated backward onto the disk surface. We apply the method on archival polarized intensity images of the protoplanetary disk around HD 100546 that were obtained with VLT/SPHERE in the R' band and VLT/NACO in the H and K-s bands. \Results. The brightest side of the r(2)-scaled R-0 band polarized intensity image of HD 100546 changes from the far to the near side of the disk when a flaring instead of a geometrically flat disk surface is used for the r(2)-scaling. The decrease in polarized surface brightness in the scattering angle range of similar to 40 degrees-70 degrees is likely a result of the dust phase function and degree of polarization which peak in different scattering angle regimes. The derived phase functions show part of a forward scattering peak, which indicates that large, aggregate dust grains dominate the scattering opacity in the disk surface. Conclusions. Projection effects of a protoplanetary disk surface need to be taken into account to correctly interpret scattered light images. Applying the correct scaling for the correction of stellar irradiation is crucial for the interpretation of the images and the derivation of the dust properties in the disk surface layer.

As the number of known exoplanetary systems has grown, it has become increasing apparent that our current understanding of planet formation is insufficient to explain the broad but distinct distributions of planets and planetary systems we observe. In particular, constructing a coherent model of planetary formation and migration within a circumstellar disc which is capable of producing both hot Jupiters or Solar System-like planetary system is high challenging. Resolved observations of where planets form and how they influence their parent discs provides essential information for tackling this important question. A promising technique for detecting close-in companions is Sparse Aperture Masking (SAM). The technique uses a mask to transform a single aperture telescope into a compact interferometric array capable of reliably detecting point sources at the diffraction limit or closer to a bright star with superior contrasts than extreme AO systems at the cost of smaller fields of view. Applying image reconstruction techniques to the interferometric information allows an observer to recover detailed structure in the circumstellar material. In this thesis I present work on the interpretation of SAM interferometry data on protoplanetary discs through the simulation of a number of scenarios expected to be commonly seen, and the application of this technique to a number of objects. Analysing data taken as part of a SAM survey of transitional and pre-transitional discs using the Keck-II/NIRC2 instrument, I detected three companion candidates within the discs of DM\,Tau, LkH\alpha\,330, and TW\,Hya, and resolved a gap in the disc around FP\,Tau as indicated by flux from the disc rim. The location of all three of the companions detected as part of the survey are positioned in interesting regions of their parent discs. The candidate, LkH\alpha\,330\,b is a potentially cavity opening companion due to its close radial proximity to the inner rim of the outer disc. DM\,Tau\,b is located immediately outside of a ring of dusty material largely responsible for the NIR comment of the disc SED, similar to TW\,Hya\,b located in a shallow gap in the dust disc outside another ring of over-dense dusty material which bounds a deep but narrow gap. Both of these companion candidates maybe migrating cores which are feeding from the enriched ring of material. I conducted a more extensive study of the pre-transitional disc, V1247\,Ori, covering three epochs and the H-, K- and L-wavebands. Complementary observations with VLT/SPHERE in H\alpha and continuum plus SMA observations in CO (2-1) and continuum were performed. The orientation and geometry of the outer disc was recovered with the SMA data and determine the direction of rotation. We image the inner rim of the outer disc in L-band SAM data, recovering the rim in all three epochs. Combining all three data sets together we form a detailed image of the rim. In H- and K-band SAM data we observe the motion of a close-in companion candidate. This motion was found to be too large to be adequately explained through a near-circular Keplerian orbit within the plane of the disc around the central star. Hence an alternate hypothesis had to be developed. I postulated that the fitted position of the companion maybe influenced by the emission from the disc rim seen in the L-band SAM data. I constructed a suite of model SAM data sets of a companion and a disc rim and found that under the right conditions the fitted separation of a companion will be larger than the true separation. Under these conditions we find the motion of the companion candidate to be consistent with a near-circular Keplerian orbit within the plane of the disc at a semi-major axis of \sim6\,au. The H\alpha data lack the necessary resolution to confirm the companion as an accreting body, but through the high contrast sensitivities enabled by the state of the art SPHERE instrument I was able to rule out any other accreting body within the gap, unless deeply embedded by the sparse population of MIR emitting dust grains previously inferred to reside within the gap. Through the combination of SAM and SMA data we constrain the 3-D orientation of the disc, and through multi-wavelength SAM observation identify a close-in companion potentially responsible for the gap clearing and asymmetric arm structures seen in previous observations of this target. During my PhD I have contributed to the field of planet formation through the identification of four new candidate protoplanets observed in the discs of pre-main sequence stars. To do so I have quantified the confidence levels of companion fits to SAM data sets and formed synthetic data from models of asymmetric structures seen in these discs. I have described for the first time the effects of extended sources of emission on the fitted results of companion searches within interferometric data sets. I have combined SAM data sets from two separate telescopes with different apertures and masks to produce reconstructed image of an illuminated disc rim with superior uv-coverage. I have used the expertise I have developed in this field to contribute to a number of other studies, including the study of the young star TYC\,8241\,2652\,1, resulting in the rejection of a sub-stellar companion as the cause of the rapid dispersal of the star`s disc. The companion candidates I have identified here should be followed up to confirm their presence and nature as accreting protoplanets. Objects such as these will provide the opportunity for more detailed study of the process of planet formation in the near future with the next generation of instruments in the JWST and E-ELT.

Thesis (Ph. D.)--University of Washington, 2005. / Vita. Includes bibliographical references (p. 166-174).

Resumo: Neste trabalho de tese exploramos a sugestão de Barge e Sommeria (1995) de captura de partículas em vórtices anticiclônicos que se formam devido a instabilidades na nebulosa proto-planetária. O problema dinâmico foi estudado através de simulações de um disco kepleriano bidimensional e incompressível. Examinamos o processo de concentração de partículas dentro de grandes vórtices através das equações do movimento para partículas individuais (com tamanho de 50 cm e 2,12 m) submetidas à gravidade solar e ao arrasto do gás nebular. Os vórtices levam à captura de um grande número de partículas. Mostramos que a eficácia das capturas não depende somente do valor do arrasto gasoso e da elongação do vórtice mas também do modelo do disco proto-planetário escolhido. Um achado muito importante nesse trabalho de tese pode começar a responder à questão sobre a formação planetária: colapso gravitacional ou coagulação? Quando incluímos a auto-gravidade, os resultados que obtivemos mostram que a acumulação das partículas dentro do vórtice é bem mais rápida. É um ponto muito importante na formação dos núcleos planetários até hoje bastante discutido. De fato, a formação dos núcleos planetários dos planetas gigantes precisa da acumulação de material maior que 1MÅ em muito pouco tempo para que o colapso ocorra antes do efeito gravitacional dentro do vórtice começar a expulsar os planetesimais A auto-gravidade até então bastante negligenciada por muitos autores pode ser uma ferramenta essencial a ser incluída no modelo de formação planetária para explicar tal fato. Outro resultado interessante que obtivemos foi que o crescimento por auto-sedimentação das partículas com tamanho sub-métrico, não é muito eficiente para formar planetesimais. Parece que os vórtices capturam partículas com um tamanho preferencial para formar planetesimais ou núcleos planetários. / Abstract: In this thesis, we explore the suggestion of Barge & Sommeria (1995) of dust-trapping in anticyclonic vortices forming due to instabilities in the protoplanetary nebula. The dynamical problem is studied through numerical simulations of a two-dimensional incompressible Keplerian disc. We examine the process of particle concentration inside large vortex through a non-collisional N body's code for individual particles (with sizes of 50 cm and 2,12 m) subject to the solar gravity and the nebular gas drag. The vortices tend to capture a large number of particles. We show that the effectiveness of these captures depend not only on the value of the gaseous drag and the elongation of the vortices but also on the model of the protoplanetary disc chosen. A very important finding in this thesis can start to answer the question of the planetary formation: gravitational collapse or coagulation? When we include the self-gravity, the results that we found show that the accumulation of particles inside the vortices is faster. It is a very important point in the formation of planetary embryo until today highly discussed. In fact, the formation of the giant planets embryo need the accumulation of more material than 1MÅ in a very short time such that the collapse occurs before the gravitational effect inside the vortices start to eject the planetesimals. Self-gravity, until now neglected by many authors could be an essential tool to be included in planetary formation model to explain such fact. Another interesting result that we got was that the growth for auto-sedimentation of particles with sub-metric size, is not very efficient to form planetesimal. It seems that vortices capture particles with a preferential size to form planetesimals or planetary cores. / Orientador: Othon Cabo Winter / Coorientador: Masayoshi Tsuchida / Banca: Ernesto Vieira Neto / Banca: Tadashi Yokoyama / Banca: Rodney da Silva Gomes / Banca: Fernando Virgilio Roig / Doutor

Aims. We numerically studied close encounters between a young stellar system hosting a massive, gravitationally fragmenting disk and an intruder diskless star with the aim of determining the evolution of fragments that have formed in the disk prior to the encounter. Methods. Numerical hydrodynamics simulations in the non-inertial frame of reference of the host star were employed to simulate the prograde and retrograde co-planar encounters. The initial configuration of the target system (star plus disk) was obtained via a separate numerical simulation featuring the gravitational collapse of a solar-mass pre-stellar core. Results. We found that close encounters can lead to the ejection of fragments that have formed in the disk of the target prior to collision. In particular, prograde encounters are more efficient in ejecting the fragments than the retrograde encounters. The masses of ejected fragments are in the brown-dwarf mass regime. They also carry away an appreciable amount of gas in their gravitational radius of influence, implying that these objects may possess extended disks or envelopes, as also previously suggested. Close encounters can also lead to the ejection of entire spiral arms, followed by fragmentation and formation of freely-floating objects straddling the planetary mass limit. However, numerical simulations with a higher resolution are needed to confirm this finding.

We present a high angular resolution (similar to 0 ''.2), high-sensitivity (sigma similar to 0.2 mJy) survey of the 870 mu m continuum emission from the circumstellar material around 49 pre-main-sequence stars in the rho Ophiuchus molecular cloud. Because most millimeter instruments have resided in the northern hemisphere, this represents the largest high-resolution, millimeter-wave survey of the circumstellar disk content of this cloud. Our survey of 49 systems comprises 63 stars; we detect disks associated with 29 single sources, 11 binaries, 3 triple systems, and 4 transition disks. We present flux and radius distributions for these systems; in particular, this is the first presentation of a reasonably complete probability distribution of disk radii at millimeter wavelengths. We also compare the flux distribution of these protoplanetary disks with that of the disk population of the Taurus-Auriga molecular cloud. We find that disks in binaries are both significantly smaller and have much less flux than their counterparts around isolated stars. We compute truncation calculations on our binary sources and find that these disks are too small to have been affected by tidal truncation and posit some explanations for this. Lastly, our survey found three candidate gapped disks, one of which is a newly identified transition disk with no signature of a dip in infrared excess in extant observations.