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Roman R. Rafikov - One of the best experts on this subject based on the ideXlab platform.
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on the planetary interpretation of multiple gaps and rings in Protoplanetary Disks seen by alma
The Astrophysical Journal, 2019Co-Authors: Ryan Miranda, Roman R. RafikovAbstract:It has been recently suggested that the multiple concentric rings and gaps discovered by ALMA in many Protoplanetary Disks may be produced by a single planet, as a result of the complex propagation and dissipation of the multiple spiral density waves it excites in the disk. Numerical efforts to verify this idea have largely utilized the so-called locally isothermal approximation with a prescribed disk temperature profile. However, in Protoplanetary Disks this approximation does not provide an accurate description of the density wave dynamics on scales of tens of au. Moreover, we show that locally isothermal simulations tend to overestimate the contrast of ring and gap features, as well as misrepresent their positions, when compared to simulations in which the energy equation is evolved explicitly. This outcome is caused by the non-conservation of the angular momentum flux of linear perturbations in locally isothermal Disks. We demonstrate this effect using simulations of locally isothermal and adiabatic Disks (with essentially identical temperature profiles) and show how the dust distributions, probed by mm wavelength observations, differ between the two cases. Locally isothermal simulations may thus underestimate the masses of planets responsible for the formation of multiple gaps and rings on scales of tens of au observed by ALMA. We suggest that caution should be exercised in using the locally isothermal simulations to explore planet-disk interaction, as well as in other studies of wave-like phenomena in astrophysical Disks.
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planet formation in stellar binaries i planetesimal dynamics in massive Protoplanetary Disks
The Astrophysical Journal, 2014Co-Authors: Roman R. Rafikov, Kedron SilsbeeAbstract:About 20% of exoplanets discovered by radial velocity surveys reside in stellar binaries. To clarify their origin one has to understand the dynamics of planetesimals in Protoplanetary Disks within binaries. The standard description, accounting for only gas drag and gravity of the companion star, has been challenged recently, as the gravity of the Protoplanetary disk was shown to play a crucial role in planetesimal dynamics. An added complication is the tendency of Protoplanetary Disks in binaries to become eccentric, giving rise to additional excitation of planetesimal eccentricity. Here, for the first time, we analytically explore the secular dynamics of planetesimals in binaries such as α Cen and γ Cep under the combined action of (1) gravity of the eccentric Protoplanetary disk, (2) perturbations due to the (coplanar) eccentric companion, and (3) gas drag. We derive explicit solutions for the behavior of planetesimal eccentricity e p in non-precessing Disks (and in precessing Disks in certain limits). We obtain the analytical form of the distribution of the relative velocities of planetesimals, which is a key input for understanding their collisional evolution. Disk gravity strongly influences relative velocities and tends to push the sizes of planetesimals colliding with comparable objects at the highest speed to small values, ~1 km. We also find that planetesimals in eccentric Protoplanetary Disks apsidally aligned with the binary orbit collide at lower relative velocities than in misaligned Disks. Our results highlight the decisive role that disk gravity plays in planetesimal dynamics in binaries.
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planet formation in stellar binaries i planetesimal dynamics in massive Protoplanetary Disks
arXiv: Earth and Planetary Astrophysics, 2014Co-Authors: Roman R. Rafikov, Kedron SilsbeeAbstract:About $20\%$ of exoplanets discovered by radial velocity surveys reside in stellar binaries. To clarify their origin one has to understand the dynamics of planetesimals in Protoplanetary Disks within binaries. The standard description, accounting for only gas drag and gravity of the companion star has been challenged recently, as the gravity of the Protoplanetary disk was shown to play a crucial role in planetesimal dynamics. An added complication is the tendency of Protoplanetary Disks in binaries to become eccentric, giving rise to additional excitation of planetesimal eccentricity. Here, for the first time, we analytically explore secular dynamics of planetesimals in binaries such as $\alpha$ Cen and $\gamma$ Cep under the combined action of (1) gravity of the eccentric Protoplanetary disk, (2) perturbations due to the (coplanar) eccentric companion, and (3) gas drag. We derive explicit solutions for the behavior of planetesimal eccentricity ${\bf e}_p$ in non-precessing Disks (and in precessing Disks in certain limits). We obtain the analytical form of the distribution of relative velocities of planetesimals, which is a key input for understanding their collisional evolution. Disk gravity strongly influences relative velocities and tends to push sizes of planetesimals colliding with comparable objects at the highest speed to small values, $\sim 1$ km. We also find that planetesimals in eccentric Protoplanetary Disks apsidally aligned with the binary orbit collide at lower relative velocities than in mis-aligned Disks. Our results highlight a decisive role that disk gravity plays in planetesimal dynamics in binaries.
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low mass planets in Protoplanetary Disks with net vertical magnetic fields the planetary wake and gap opening
The Astrophysical Journal, 2013Co-Authors: Zhaohuan Zhu, James M Stone, Roman R. RafikovAbstract:Some regions in Protoplanetary Disks are turbulent, while some regions are quiescent (e.g. the dead zone). In order to study how planets open gaps in both inviscid hydrodynamic disk (e.g. the dead zone) and the disk subject to magnetorotational instability (MRI), we carried out both shearing box two-dimensional inviscid hydrodynamical simulations and three-dimensional unstratified magnetohydrodynamical (MHD) simulations (having net vertical magnetic fields) with a planet at the box center. We found that, due to the nonlinear wave steepening, even a low mass planet can open gaps in both cases, in contradiction to the "thermal criterion" for gap opening. In order to understand if we can represent the MRI turbulent stress with the viscous α prescription for studying gap opening, we compare gap properties in MRI-turbulent Disks to those in viscous HD Disks having the same stress, and found that the same mass planet opens a significantly deeper and wider gap in net vertical flux MHD Disks than in viscous HD Disks. This difference arises due to the efficient magnetic field transport into the gap region in MRI Disks, leading to a larger effective α within the gap. Thus, across the gap, the Maxwell stress profile is smoother than the gap density profile, and a deeper gap is needed for the Maxwell stress gradient to balance the planetary torque density. Comparison with previous results from net toroidal flux/zero flux MHD simulations indicates that the magnetic field geometry plays an important role in the gap opening process. We also found that long-lived density features (termed zonal flows) produced by the MRI can affect planet migration. Overall, our results suggest that gaps can be commonly produced by low mass planets in realistic Protoplanetary Disks, and caution the use of a constant α-viscosity to model gaps in Protoplanetary Disks.
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low mass planets in Protoplanetary Disks with net vertical magnetic fields the planetary wake and gap opening
arXiv: Solar and Stellar Astrophysics, 2013Co-Authors: Zhaohuan Zhu, James M Stone, Roman R. RafikovAbstract:We study wakes and gap opening by low mass planets in gaseous Protoplanetary Disks threaded by net vertical magnetic fields which drive magnetohydrodynamical (MHD) turbulence through the magnetorotational instabilty (MRI), using three dimensional simulations in the unstratified local shearing box approximation. The wakes, which are excited by the planets, are damped by shocks similar to the wake damping in inviscid hydrodynamic (HD) Disks. Angular momentum deposition by shock damping opens gaps in both MHD turbulent Disks and inviscid HD Disks even for low mass planets, in contradiction to the "thermal criterion" for gap opening. To test the "viscous criterion", we compared gap properties in MRI-turbulent Disks to those in viscous HD Disks having the same stress, and found that the same mass planet opens a significantly deeper and wider gap in net vertical flux MHD Disks than in viscous HD Disks. This difference arises due to the efficient magnetic field transport into the gap region in MRI Disks, leading to a larger effective \alpha within the gap. Thus, across the gap, the Maxwell stress profile is smoother than the gap density profile, and a deeper gap is needed for the Maxwell stress gradient to balance the planetary torque density. We also confirmed the large excess torque close to the planet in MHD Disks, and found that long-lived density features (termed zonal flows) produced by the MRI can affect planet migration. The comparison with previous results from net toroidal flux/zero flux MHD simulations indicates that the magnetic field geometry plays an important role in the gap opening process. Overall, our results suggest that gaps can be commonly produced by low mass planets in realistic Protoplanetary Disks, and caution the use of a constant \alpha-viscosity to model gaps in Protoplanetary Disks.
Hideko Nomura - One of the best experts on this subject based on the ideXlab platform.
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radiative grain alignment in Protoplanetary Disks implications for polarimetric observations
The Astrophysical Journal, 2017Co-Authors: A Lazarian, Ryo Tazaki, Hideko NomuraAbstract:We apply the theory of radiative torque (RAT) alignment for studying Protoplanetary Disks around a T-Tauri star and perform 3D radiative transfer calculations to provide the expected maps of polarized radiation to be compared with observations, such as with ALMA. We revisit the issue of grain alignment for large grains expected in the Protoplanetary Disks and find that mm-sized grains at midplane do not align with the magnetic field as the Larmor precession timescale for such large grains becomes longer than the gaseous damping timescale. Hence, for these grains the RAT theory predicts that the alignment axis is determined by the grain precession with respect to the radiative flux. As a result, we expect that the polarization will be in the azimuthal direction for a face-on disk. It is also shown that if dust grains have superparamagnetic inclusions, magnetic field alignment is possible for (sub-)micron grains at the surface layer of Disks, and this can be tested by mid-infrared polarimetric observations.
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Complex organic molecules in Protoplanetary Disks
Astronomy & Astrophysics, 2014Co-Authors: Catherine Walsh, Hideko Nomura, Thomas J. Millar, Eric Herbst, Yuri Aikawa, Jacob C Laas, Susanna L. Widicus Weaver, Anton I. VasyuninAbstract:(Abridged) Protoplanetary Disks are vital objects in star and planet formation, possessing all the material which may form a planetary system orbiting the new star. We investigate the synthesis of complex organic molecules (COMs) in Disks to constrain the achievable chemical complexity and predict species and transitions which may be observable with ALMA. We have coupled a 2D model of a Protoplanetary disk around a T Tauri star with a gas-grain chemical network including COMs. We compare compare synthesised line intensities and calculated column densities with observations and determine those COMs which may be observable in future. COMs are efficiently formed in the disk midplane via grain-surface chemical reactions, reaching peak grain-surface fractional abundances 1e-6 - 1e-4 that of the H nuclei number density. COMs formed on grain surfaces are returned to the gas phase via non-thermal desorption; however, gas-phase species reach lower fractional abundances than their grain-surface equivalents, 1e-12 - 1e-7. Including the irradiation of grain mantle material helps build further complexity in the ice through the replenishment of grain-surface radicals which take part in further grain-surface reactions. There is reasonable agreement with several line transitions of H2CO observed towards several T Tauri star-disk systems. The synthesised line intensities for CH3OH are consistent with upper limits determined towards all sources. Our models suggest CH3OH should be readily observable in nearby Protoplanetary Disks with ALMA; however, detection of more complex species may prove challenging. Our grain-surface abundances are consistent with those derived from cometary comae observations providing additional evidence for the hypothesis that comets (and other planetesimals) formed via the coagulation of icy grains in the Sun's natal disk.
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complex organic molecules in Protoplanetary Disks
prpl, 2013Co-Authors: Hideko Nomura, Catherine Walsh, T J Millar, Eric Herbst, Susanna Widicus L Weaver, Yuri Aikawa, Jacob C LaasAbstract:Context. Protoplanetary Disks are vital objects in star and planet formation, possessing all the material, gas and dust, which may form a planetary system orbiting the new star. Small, simple molecules have traditionally been detected in Protoplanetary Disks; however, in the ALMA era, we expect the molecular inventory of Protoplanetary Disks to significantly increase. Aims. We investigate the synthesis of complex organic molecules (COMs) in Protoplanetary Disks to put constraints on the achievable chemical complexity and to predict species and transitions which may be observable with ALMA. Methods. We have coupled a 2D steady-state physical model of a Protoplanetary disk around a typical T Tauri star with a large gas-grain chemical network including COMs. We compare the resulting column densities with those derived from observations and perform ray-tracing calculations to predict line spectra. We compare the synthesised line intensities with current observations and determine those COMs which may be observable in nearby objects. We also compare the predicted grain-surface abundances with those derived from cometary comae observations. Results. We find COMs are efficiently formed in the disk midplane via grain-surface chemical reactions, reaching peak grain-surface fractional abundances ~10-6–10-4 that of the H nuclei number density. COMs formed on grain surfaces are returned to the gas phase via non-thermal desorption; however, gas-phase species reach lower fractional abundances than their grain-surface equivalents, ~10-12–10-7. Including the irradiation of grain mantle material helps build further complexity in the ice through the replenishment of grain-surface radicals which take part in further grain-surface reactions. There is reasonable agreement with several line transitions of H2CO observed towards T Tauri star-disk systems. There is poor agreement with HC3N lines observed towards LkCa 15 and GO Tau and we discuss possible explanations for these discrepancies. The synthesised line intensities for CH3OH are consistent with upper limits determined towards all sources. Our models suggest CH3OH should be readily observable in nearby Protoplanetary Disks with ALMA; however, detection of more complex species may prove challenging, even with ALMA “Full Science” capabilities. Our grain-surface abundances are consistent with those derived from cometary comae observations providing additional evidence for the hypothesis that comets (and other planetesimals) formed via the coagulation of icy grains in the Sun’s natal disk.
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molecular hydrogen emission from Protoplanetary Disks ii effects of x ray irradiation and dust evolution
The Astrophysical Journal, 2007Co-Authors: Hideko Nomura, Yuri Aikawa, Masahiro Tsujimoto, Yoshitsugu Nakagawa, T J MillarAbstract:Detailed models for the density and temperature profiles of gas and dust in Protoplanetary Disks are constructed by taking into account X-ray and UV irradiation from a central T Tauri star, as well as dust size growth and settling toward the disk midplane. The spatial and size distributions of dust grains are numerically computed by solving the coagulation equation for settling dust particles, with the result that the mass and total surface area of dust grains per unit volume of the gas in the Disks are very small, except at the midplane. The H2 level populations and line emission are calculatedusingthederivedphysicalstructureoftheDisks.X-rayirradiationisthedominantheatingsource ofthegas in the inner disk and in the surface layer, while the UV heating dominates otherwise. If the central star has strong X-ray and weak UV radiation, the H2 level populations are controlled by X-ray pumping, and the X-rayYinduced transition lines could be observable. If the UVirradiation is strong, the level populations are controlled by thermal collisions or UVpumping,depending onthe dustproperties. Asthedustparticlesevolveinthe Disks,the gastemperatureatthe disk surface drops because the grain photoelectric heating becomes less efficient. This makes the level populations change fromLTEtonon-LTEdistributions,whichresultsinchangestothelineratios.Our resultssuggest thatdustevolutionin Protoplanetary Disks could be observable through the H2 line ratios. The emission lines are strong from Disks irradiated by strong UV and X-rays and possessing small dust grains; such Disks will be good targets in which to observe H2 emission. Subject headingg line: formation — molecular processes — planetary systems: Protoplanetary Disks — radiative transfer
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physical and chemical structure of Protoplanetary Disks with grain growth
The Astrophysical Journal, 2006Co-Authors: Yuri Aikawa, Hideko NomuraAbstract:We calculate the physical structure of Protoplanetary Disks by evaluating the gas density and temperature selfconsistently and solving separately for the dust temperature. The effect of grain growth is taken into account by assuming a power-law size distribution and varying the maximum radius of grains amax. In our fiducial model with amax ¼ 10 � m, the gas is warmer than the dust in the surface layer of the disk, while the gas and dust have the same temperature in deeper layers. In the modelswith largeramax, the gastemperature in the surface layer islowerthanin the fiducial model because of reduced photoelectric heating rates from small grains, while the deeper penetration of stellar radiation warms the gas at intermediate height. A detailed chemical reaction network is solved at outer radii (r � 50 AU). Vertical distributions of some molecular species at different radii are similar when plotted as a function of hydrogen column density H from the disk surface. Consequently, molecular column densities do not much depend on disk radius. In the models with larger amax, the lower temperature in the surface layer makes the geometrical thickness of the disk smaller, and the gaseous molecules are confined to smaller heights. However, if we plot the vertical distributions of molecules as a function of H, they do not significantly depend on amax .T he dependence of the molecular column densities on amax is not significant either. Notable exceptions are HCO þ ,H þ , and H2D þ , which have smaller column densities in the models with larger amax. Subject headingg ISM: molecules — planetary systems: Protoplanetary Disks — stars: pre‐main-sequence
Christoph Olczak - One of the best experts on this subject based on the ideXlab platform.
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from dust to planetesimals an improved model for collisional growth in Protoplanetary Disks
The Astrophysical Journal, 2013Co-Authors: Pascale Garaud, Farzana Meru, Marina Galvagni, Christoph OlczakAbstract:Planet formation occurs within the gas- and dust-rich environments of Protoplanetary Disks. Observations of these objects show that the growth of primordial submicron-sized particles into larger aggregates occurs at the earliest evolutionary stages of the Disks. However, theoretical models of particle growth that use the Smoluchowski equation to describe collisional coagulation and fragmentation have so far failed to produce large particles while maintaining a significant population of small grains. This has generally been attributed to the existence of two barriers impeding growth due to bouncing and fragmentation of colliding particles. In this paper, we demonstrate that the importance of these barriers has been artificially inflated through the use of simplified models that do not take into account the stochastic nature of the particle motions within the gas disk. We present a new approach in which the relative velocities between two particles are described by a probability distribution function that models both deterministic motion (from the vertical settling, radial drift, and azimuthal drift) and stochastic motion (from Brownian motion and turbulence). Taking both into account can give quite different results to what has been considered recently in other studies. We demonstrate the vital effect of two ingredients for particle growth: the proper implementation of a velocity distribution function that overcomes the bouncing barrier and, in combination with mass transfer in high-mass-ratio collisions, boosts the growth of larger particles beyond the fragmentation barrier. A robust result of our simulations is the emergence of two particle populations (small and large), potentially explaining simultaneously a number of longstanding problems in Protoplanetary Disks, including planetesimal formation close to the central star, the presence of?millimeter- to centimeter-sized particles far out in the disk, and the persistence of ?m-sized grains for millions of years.
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from dust to planetesimals an improved model for collisional growth in Protoplanetary Disks
arXiv: Earth and Planetary Astrophysics, 2012Co-Authors: Pascale Garaud, Farzana Meru, Marina Galvagni, Christoph OlczakAbstract:Planet formation occurs within the gas and dust rich environments of Protoplanetary Disks. Observations of these objects show that the growth of primordial sub micron sized particles into larger aggregates occurs at the earliest stages of the Disks. However, theoretical models of particle growth that use the Smoluchowski equation to describe collisional coagulation and fragmentation have so far failed to produce large particles while maintaining a significant populations of small grains. This has been generally attributed to the existence of two barriers impeding growth due to bouncing and fragmentation of colliding particles. In this paper, we demonstrate that the importance of these barriers has been artificially inflated through the use of simplified models that do not take into account the stochastic nature of the particle motions within the gas disk. We present a new approach in which the relative velocities between two particles is described by a probability distribution function that models both deterministic motion and stochastic motion. Taking both into account can give quite different results to what has been considered recently in other studies. We demonstrate the vital effect of two "ingredients" for particle growth: the proper implementation of a velocity distribution function that overcomes the bouncing barrier and, in combination with mass transfer in high-mass-ratio collisions, boosts the growth of larger particles beyond the fragmentation barrier. A robust result of our simulations is the emergence of two particle populations (small and large), potentially explaining simultaneously a number of long-standing problems in Protoplanetary Disks, including planetesimal formation close to the central star, the presence of mm to cm size particles far out in the disk, and the persistence of micron-size grains for millions of years.
Kedron Silsbee - One of the best experts on this subject based on the ideXlab platform.
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planet formation in stellar binaries i planetesimal dynamics in massive Protoplanetary Disks
The Astrophysical Journal, 2014Co-Authors: Roman R. Rafikov, Kedron SilsbeeAbstract:About 20% of exoplanets discovered by radial velocity surveys reside in stellar binaries. To clarify their origin one has to understand the dynamics of planetesimals in Protoplanetary Disks within binaries. The standard description, accounting for only gas drag and gravity of the companion star, has been challenged recently, as the gravity of the Protoplanetary disk was shown to play a crucial role in planetesimal dynamics. An added complication is the tendency of Protoplanetary Disks in binaries to become eccentric, giving rise to additional excitation of planetesimal eccentricity. Here, for the first time, we analytically explore the secular dynamics of planetesimals in binaries such as α Cen and γ Cep under the combined action of (1) gravity of the eccentric Protoplanetary disk, (2) perturbations due to the (coplanar) eccentric companion, and (3) gas drag. We derive explicit solutions for the behavior of planetesimal eccentricity e p in non-precessing Disks (and in precessing Disks in certain limits). We obtain the analytical form of the distribution of the relative velocities of planetesimals, which is a key input for understanding their collisional evolution. Disk gravity strongly influences relative velocities and tends to push the sizes of planetesimals colliding with comparable objects at the highest speed to small values, ~1 km. We also find that planetesimals in eccentric Protoplanetary Disks apsidally aligned with the binary orbit collide at lower relative velocities than in misaligned Disks. Our results highlight the decisive role that disk gravity plays in planetesimal dynamics in binaries.
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planet formation in stellar binaries i planetesimal dynamics in massive Protoplanetary Disks
arXiv: Earth and Planetary Astrophysics, 2014Co-Authors: Roman R. Rafikov, Kedron SilsbeeAbstract:About $20\%$ of exoplanets discovered by radial velocity surveys reside in stellar binaries. To clarify their origin one has to understand the dynamics of planetesimals in Protoplanetary Disks within binaries. The standard description, accounting for only gas drag and gravity of the companion star has been challenged recently, as the gravity of the Protoplanetary disk was shown to play a crucial role in planetesimal dynamics. An added complication is the tendency of Protoplanetary Disks in binaries to become eccentric, giving rise to additional excitation of planetesimal eccentricity. Here, for the first time, we analytically explore secular dynamics of planetesimals in binaries such as $\alpha$ Cen and $\gamma$ Cep under the combined action of (1) gravity of the eccentric Protoplanetary disk, (2) perturbations due to the (coplanar) eccentric companion, and (3) gas drag. We derive explicit solutions for the behavior of planetesimal eccentricity ${\bf e}_p$ in non-precessing Disks (and in precessing Disks in certain limits). We obtain the analytical form of the distribution of relative velocities of planetesimals, which is a key input for understanding their collisional evolution. Disk gravity strongly influences relative velocities and tends to push sizes of planetesimals colliding with comparable objects at the highest speed to small values, $\sim 1$ km. We also find that planetesimals in eccentric Protoplanetary Disks apsidally aligned with the binary orbit collide at lower relative velocities than in mis-aligned Disks. Our results highlight a decisive role that disk gravity plays in planetesimal dynamics in binaries.
L Testi - One of the best experts on this subject based on the ideXlab platform.
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constraints from dust mass and mass accretion rate measurements on angular momentum transport in Protoplanetary Disks
arXiv: Solar and Stellar Astrophysics, 2017Co-Authors: Gijs D Mulders, Ilaria Pascucci, C F Manara, L Testi, Gregory J Herczeg, Thomas Henning, Subhanjoy Mohanty, Giuseppe LodatoAbstract:We investigate the relation between disk mass and mass accretion rate to constrain the mechanism of angular momentum transport in Protoplanetary Disks. Dust mass and mass accretion rate in Chamaeleon I are correlated with a slope close to linear, similar to the one recently identified in Lupus. We investigate the effect of stellar mass and find that the intrinsic scatter around the best-fit Mdust-Mstar and Macc-Mstar relations is uncorrelated. Disks with a constant alpha viscosity can fit the observed relations between dust mass, mass accretion rate, and stellar mass, but over-predict the strength of the correlation between disk mass and mass accretion rate when using standard initial conditions. We find two possible solutions. 1) The observed scatter in Mdust and Macc is not primoridal, but arises from additional physical processes or uncertainties in estimating the disk gas mass. Most likely grain growth and radial drift affect the observable dust mass, while variability on large time scales affects the mass accretion rates. 2) The observed scatter is primordial, but Disks have not evolved substantially at the age of Lupus and Chamaeleon I due to a low viscosity or a large initial disk radius. More accurate estimates of the disk mass and gas disk sizes in a large sample of Protoplanetary Disks, either through direct observations of the gas or spatially resolved multi-wavelength observations of the dust with ALMA, are needed to discriminate between both scenarios or to constrain alternative angular momentum transport mechanisms such as MHD disk winds.
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physical properties of dusty Protoplanetary Disks in lupus evidence for viscous evolution
arXiv: Earth and Planetary Astrophysics, 2017Co-Authors: L Testi, Megan Ansdell, G Guidi, M Tazzari, A Natta, J M CarpenterAbstract:The formation of planets strongly depends on the total amount as well as on the spatial distribution of solids in Protoplanetary Disks. Thanks to the improvements in resolution and sensitivity provided by ALMA, measurements of the surface density of mm-sized grains are now possible on large samples of Disks. Such measurements provide statistical constraints that can be used to inform our understanding of the initial conditions of planet formation. We analyze spatially resolved observations of 36 Protoplanetary Disks in the Lupus star forming complex from our ALMA survey at 890 micron, aiming to determine physical properties such as the dust surface density, the disk mass and size and to provide a constraint on the temperature profile. We fit the observations directly in the uv-plane using a two-layer disk model that computes the 890 micron emission by solving the energy balance at each disk radius. For 22 out of 36 Protoplanetary Disks we derive robust estimates of their physical properties. The sample covers stellar masses between ~0.1 and ~2 Solar masses, and we find no trend between the average disk temperatures and the stellar parameters. We find, instead, a correlation between the integrated sub-mm flux (a proxy for the disk mass) and the exponential cut-off radii (a proxy of the disk size) of the Lupus Disks. Comparing these results with observations at similar angular resolution of Taurus-Auriga/Ophiuchus Disks found in literature and scaling them to the same distance, we observe that the Lupus Disks are generally fainter and larger at a high level of statistical significance. Considering the 1-2 Myr age difference between these regions, it is possible to tentatively explain the offset in the disk mass/disk size relation with viscous spreading, however with the current measurements other mechanisms cannot be ruled out.
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an alma survey of co isotopologue emission from Protoplanetary Disks in chamaeleon i
arXiv: Solar and Stellar Astrophysics, 2017Co-Authors: Feng Long, Ilaria Pascucci, L Testi, Gregory J Herczeg, Thomas Henning, Subhanjoy Mohanty, E Drabekmaunder, Daniel Apai, Nathan Hendler, C F ManaraAbstract:The mass of a Protoplanetary disk limits the formation and future growth of any planet. Masses of Protoplanetary Disks are usually calculated from measurements of the dust continuum emission by assuming an interstellar gas-to-dust ratio. To investigate the utility of CO as an alternate probe of disk mass, we use ALMA to survey $^{13}$CO and C$^{18}$O J = $3-2$ line emission from a sample of 93 Protoplanetary Disks around stars and brown dwarfs with masses from 0.03 -- 2 M$_{\odot}$ in the nearby Chamaeleon I star-forming region. We detect $^{13}$CO emission from 17 sources and C$^{18}$O from only one source. Gas masses for Disks are then estimated by comparing the CO line luminosities to results from published disk models that include CO freeze-out and isotope-selective photodissociation. Under the assumption of a typical ISM CO-to-H$_2$ ratios of $10^{-4}$, the resulting gas masses are implausibly low, with an average gas mass of $\sim$ 0.05 M$_{Jup}$ as inferred from the average flux of stacked $^{13}$CO lines. The low gas masses and gas-to-dust ratios for Cha I Disks are both consistent with similar results from Disks in the Lupus star-forming region. The faint CO line emission may instead be explained if Disks have much higher gas masses, but freeze-out of CO or complex C-bearing molecules is underestimated in disk models. The conversion of CO flux to CO gas mass also suffers from uncertainties in disk structures, which could affect gas temperatures. CO emission lines will only be a good tracer of the disk mass when models for C and CO depletion are confirmed to be accurate.
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dust grain growth in ρ ophiuchi Protoplanetary Disks
Astronomy and Astrophysics, 2010Co-Authors: L Ricci, L Testi, A Natta, Kate BrooksAbstract:We present new ATCA observations at 3.3 mm of 27 young stellar objects in the ρ-Oph young cluster. 25 of these sources have been detected. We analyze the sub-millimeter and millimeter SED for a subsample of 17 isolated class II Protoplanetary Disks and derive constraints on the grain growth and total dust mass in the disk outer regions. All the Disks in our sample show a mm slope of the SED which is significantly shallower than the one observed for the ISM at these long wavelengths. This indicates that 1) class II Disks in Ophiuchus host grains grown to mm/cm-sizes in their outer regions; 2) formation of mm/cm-sized pebbles is a fast process and 3) a mechanism halting or slowing down the inward radial drift of solid particles is required to explain the data. These findings are consistent with previous results in other star forming regions. We compare the dust properties of this sample with those of a uniformly selected sample in Taurus-Auriga and find no statistical evidence of any difference in terms of grain growth between the two regions. Finally, in our sample the mm slope of the SED is not found to correlate with indicators of grain growth to micron sizes in the surface layers of the inner disk.
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dust grain growth in rho ophiuchi Protoplanetary Disks
arXiv: Solar and Stellar Astrophysics, 2010Co-Authors: L Ricci, L Testi, A Natta, Kate J BrooksAbstract:We present new ATCA observations at 3.3 mm of 27 young stellar objects in the rho-Oph young cluster. 25 of these sources have been detected. We analyze the sub-millimeter and millimeter SED for a subsample of 17 isolated class II Protoplanetary Disks and derive constraints on the grain growth and total dust mass in the disk outer regions. All the Disks in our sample show a mm slope of the SED which is significantly shallower than the one observed for the ISM at these long wavelengths. This indicates that 1) class II Disks in Ophiuchus host grains grown to mm/cm-sizes in their outer regions, 2) formation of mm/cm-sized pebbles is a fast process and 3) a mechanism halting or slowing down the inward radial drift of solid particles is required to explain the data. These findings are consistent with previous results in other star forming regions. We compare the dust properties of this sample with those of a uniformly selected sample in Taurus-Auriga and find no statistical evidence of any difference in terms of grain growth between the two regions. Finally, in our sample the mm slope of the SED is not found to correlate with indicators of grain growth to micron sizes in the surface layers of the inner disk.
