A dual-frequency sub-arcsecond study of proto-planetary disks at mm wavelengths: first evidence for radial variations of the dust properties
TL;DR: In this article, the radial distribution of dust in disks around a sample of young stars from an observational point of view, and, when possible, in a model-independent way, by using parametric laws.
Abstract: Context. Proto-planetary disks are thought to provide the initial environment for planetary system formation. The dust and gas distribution and its evolution with time is one of the key elements in the process.Aims. We attempt to characterize the radial distribution of dust in disks around a sample of young stars from an observational point of view, and, when possible, in a model-independent way, by using parametric laws.Methods. We used the IRAM PdBI interferometer to provide very high angular resolution (down to 0.4′′ in some sources) observations of the continuum at 1.3 mm and 3 mm around a sample of T Tauri stars in the Taurus-Auriga region. The sample includes single and multiple systems, with a total of 23 individual disks. We used track-sharing observing mode to minimize the biases. We fitted these data with two kinds of models: a “truncated power law” model and a model presenting an exponential decay at the disk edge (“viscous” model).Results. Direct evidence for tidal truncation is found in the multiple systems. The temperature of the mm-emitting dust is constrained in a few systems. Unambiguous evidence for large grains is obtained by resolving out disks with very low values of the dust emissivity index β . In most disks that are sufficiently resolved at two different wavelengths, we find a radial dependence of β , which appears to increase from low values (as low as 0) at the center to about 1.7−2 at the disk edge. The same behavior could apply to all studied disks. It introduces further ambiguities in interpreting the brightness profile, because the regions with apparent β ≈ 0 can also be interpreted as being optically thick when their brightness temperature is high enough. Despite the added uncertainty on the dust absorption coefficient, the characteristic size of the disk appears to increase with a higher estimated star age. Conclusions. These results provide the first direct evidence of the radial dependence of the grain size in proto-planetary disks. Constraints of the surface density distributions and their evolution remain ambiguous because of a degeneracy with the β (r ) law.
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TL;DR: In this paper, the Atacama Large Millimeter/submillimeter Array (ALMA) observations from the 2014 Long Baseline Campaign in dust continuum and spectral line emission from the HL Tau region were presented.
Abstract: We present Atacama Large Millimeter/submillimeter Array (ALMA) observations from the 2014 Long Baseline Campaign in dust continuum and spectral line emission from the HL Tau region. The continuum images at wavelengths of 2.9, 1.3, and 0.87 mm have unprecedented angular resolutions of 0.″ 075 (10 AU) to 0.″ 025 (3.5 AU), revealing an astonishing level of detail in the circumstellar disk surrounding the young solar analog HL Tau, with a pattern of bright and dark rings observed at all wavelengths. By fitting ellipses to the most distinct rings, we measure precise values for the disk inclination (46\buildrel{\circ}\over{.} 72+/- 0\buildrel{\circ}\over{.} 05) and position angle (+138\buildrel{\circ}\over{.} 02+/- 0\buildrel{\circ}\over{.} 07). We obtain a high-fidelity image of the 1.0 mm spectral index (α), which ranges from α ∼ 2.0 in the optically thick central peak and two brightest rings, increasing to 2.3–3.0 in the dark rings. The dark rings are not devoid of emission, and we estimate a grain emissivity index of 0.8 for the innermost dark ring and lower for subsequent dark rings, consistent with some degree of grain growth and evolution. Additional clues that the rings arise from planet formation include an increase in their central offsets with radius and the presence of numerous orbital resonances. At a resolution of 35 AU, we resolve the molecular component of the disk in HCO+ (1-0) which exhibits a pattern over LSR velocities from 2–12 km s‑1 consistent with Keplerian motion around a ∼1.3 {M}ȯ star, although complicated by absorption at low blueshifted velocities. We also serendipitously detect and resolve the nearby protostars XZ Tau (A/B) and LkHα358 at 2.9 mm.
1,157 citations
TL;DR: In this paper, the Atacama Large Millimeter/submillimeter Array (ALMA) observations from the 2014 Long Baseline Campaign in dust continuum and spectral line emission from the HL Tau region were presented.
Abstract: We present Atacama Large Millimeter/submillimeter Array (ALMA) observations from the 2014 Long Baseline Campaign in dust continuum and spectral line emission from the HL Tau region. The continuum images at wavelengths of 2.9, 1.3, and 0.87 mm have unprecedented angular resolutions of 0. ′′ 075 (10 AU) to 0. ′′ 025 (3.5 AU), revealing an astonishing level of detail in the cir cumstellar disk surrounding the young solar analogue HL Tau, with a pattern of bright and dark rings observed at all wavelengths. By fitting ellipses to the most distinct rings, we measure precise values for the disk inclination (46.72 ◦ ± 0.05 ◦ ) and position angle (+138.02 ◦ ± 0.07 ◦ ). We obtain a high-fidelity image of the 1.0 mm spectral index (�), which ranges from � � 2.0 in the optically-thick central peak and two brightest ring s, increasing to 2.3-3.0 in the dark rings. The dark rings are not devoid of emission, and we estimate a grain emissivity index of 0.8 for the innermost dark ring and lower for subsequent dark rings, consistent with some degree of grain growth and evolution. Additional clues that the rings arise from planet formation incl ude an increase in their central offsets with radius and the presence of numerous orbital resonances. At a resolution of 35 AU, we resolve the molecular component of the disk in HCO + (1-0) which exhibits a pattern over LSR velocities from 2-12 km s -1 consistent with Keplerian motion around a �1.3M⊙ star, although complicated by absorption at low blue-shifted velocities. We also serendipitously detect and resolve the nearby protost ars XZ Tau (A/B) and LkH�358 at 2.9 mm. Subject headings: stars: individual (HL Tau, XZ Tau, LkH�358) — protoplanetary disks — stars: formation — submillimeter: planetary systems — techniques: interferometric
1,003 citations
Cites background or methods or result from "A dual-frequency sub-arcsecond stud..."
...…at these wavelengths (Andrews & Williams 2005); hence HL Tau has been a favored interferometric target over the last two decades (Sargent & Beckwith 1991; Mundy et al. 1996; Lay et al. 1997; Kitamura et al. 2002; Looney et al. 2000; Guilloteau et al. 2011; Stephens et al. 2014, to name a few)....
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...We do not find a gradual decrement of the spectral index with radius reported in other lower mass protoplanetary systems, albeit with reduced angular resolution (e.g. Guilloteau et al. 2011; Pérez et al. 2012)....
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...Modeling of previous millimeter data suggest an HL Tau disk mass ofMd ∼ 0.03− 0.14 M⊙ (Robitaille et al. 2007; Guilloteau et al. 2011; Kwon et al. 2011)....
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...For comparison, Guilloteau et al. (2011) foundTB = 25 K at 55 AU from ∼ 1′′ resolution PdBI data in good agreement with that predicted from the ALMATB analysis....
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...Considering recent interferometric observations, 2.7 mm flux densities range from 94.1±0.9 to 120±4 mJy and 1.3 mm flux densities range from 700±10 to 818±10.8 mJy (Kwon et al. 2011; Guilloteau et al. 2011)....
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Harvard University1, University of Chile2, Rice University3, Heidelberg University4, Pontifical Catholic University of Chile5, University of Nevada, Las Vegas6, Ludwig Maximilian University of Munich7, Tsinghua University8, University of Grenoble9, Wesleyan University10, California State University, Northridge11
TL;DR: The Disk Substructures at High Angular Resolution Project (DSHARP) as mentioned in this paper was the first large-scale project to find and characterize substructures in the spatial distributions of solid particles for a sample of 20 nearby protoplanetary disks, using very high resolution (similar to 0'' 035 or 5 au, FWHM) observations of their 240 GHz (1.25 mm) continuum emission.
Abstract: We introduce the Disk Substructures at High Angular Resolution Project (DSHARP), one of the initial Large Programs conducted with the Atacama Large Millimeter/submillimeter Array (ALMA). The primary goal of DSHARP is to find and characterize substructures in the spatial distributions of solid particles for a sample of 20 nearby protoplanetary disks, using very high resolution (similar to 0.'' 035, or 5 au, FWHM) observations of their 240 GHz (1.25 mm) continuum emission. These data provide a first homogeneous look at the small-scale features in disks that are directly relevant to the planet formation process, quantifying their prevalence, morphologies, spatial scales, spacings, symmetry, and amplitudes, for targets with a variety of disk and stellar host properties. We find that these substructures are ubiquitous in this sample of large, bright disks. They are most frequently manifested as concentric, narrow emission rings and depleted gaps, although large-scale spiral patterns and small arc-shaped azimuthal asymmetries are also present in some cases. These substructures are found at a wide range of disk radii (from a few astronomical units to more than 100 au), are usually compact (less than or similar to 10 au), and show a wide range of amplitudes (brightness contrasts). Here we discuss the motivation for the project, describe the survey design and the sample properties, detail the observations and data calibration, highlight some basic results, and provide a general overview of the key conclusions that are presented in more detail in a series of accompanying articles. The DSHARP data-including visibilities, images, calibration scripts, and more-are released for community use at https://almascience.org/alma-data/lp/DSHARP.
822 citations
Cites background from "A dual-frequency sub-arcsecond stud..."
...Resolved variations in the continuum spectrum shape have been interpreted as radial gradients in the particle size distributions (larger solids closer to the star; Isella et al. 2010; Guilloteau et al. 2011; Pérez et al. 2012, 2015; Menu et al. 2014; Tazzari et al. 2016; Tripathi et al. 2018)....
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TL;DR: In this article, the authors presented a substantial extension of the mm wave photometry catalog for circumstellar dust disks in the Taurus star-forming region, based on a new ''snapshot'' {lambda} = 1.3 mm survey with the Submillimeter Array.
Abstract: We present a substantial extension of the millimeter (mm) wave continuum photometry catalog for circumstellar dust disks in the Taurus star-forming region, based on a new ''snapshot'' {lambda} = 1.3 mm survey with the Submillimeter Array. Combining these new data with measurements in the literature, we construct a mm-wave luminosity distribution, f(L{sub mm}), for Class II disks that is statistically complete for stellar hosts with spectral types earlier than M8.5 and has a 3{sigma} depth of roughly 3 mJy. The resulting census eliminates a longstanding selection bias against disks with late-type hosts, and thereby demonstrates that there is a strong correlation between L{sub mm} and the host spectral type. By translating the locations of individual stars in the Hertzsprung-Russell diagram into masses and ages, and adopting a simple conversion between L{sub mm} and the disk mass, M{sub d} , we confirm that this correlation corresponds to a statistically robust relationship between the masses of dust disks and the stars that host them. A Bayesian regression technique is used to characterize these relationships in the presence of measurement errors, data censoring, and significant intrinsic scatter: the best-fit results indicate a typical 1.3 mm flux density of {approx}25 mJy for 1 M{submore » Sun} hosts and a power-law scaling L{sub mm}{proportional_to}M{sub *}{sup 1.5-2.0}. We suggest that a reasonable treatment of dust temperature in the conversion from L{sub mm} to M{sub d} favors an inherently linear M{sub d} {proportional_to}M{sub *} scaling, with a typical disk-to-star mass ratio of {approx}0.2%-0.6%. The measured rms dispersion around this regression curve is {+-}0.7 dex, suggesting that the combined effects of diverse evolutionary states, dust opacities, and temperatures in these disks imprint a full width at half-maximum range of a factor of {approx}40 on the inferred M{sub d} (or L{sub mm}) at any given host mass. We argue that this relationship between M{sub d} and M{sub *} likely represents the origin of the inferred correlation between giant planet frequency and host star mass in the exoplanet population, and provides some basic support for the core accretion model for planet formation. Moreover, we caution that the effects of incompleteness and selection bias must be considered in comparative studies of disk evolution, and illustrate that fact with statistical comparisons of f(L{sub mm}) between the Taurus catalog presented here and incomplete subsamples in the Ophiuchus, IC 348, and Upper Sco young clusters.« less
640 citations
TL;DR: In this paper, the presence of a large planet in a disk influences the growth and radial distribution of dust grains, and how observable properties are linked to the mass of the planet, and they combined two-dimensional hydrodynamical disk simulations of disk-planet interactions with state-of-the-art coagulation/fragmentation models to simulate the evolution of dust in a transition disk, which has a gap created by a massive planet.
Abstract: Context. Transition disks are believed to be the final stages of protoplanetary disks, during which a forming planetary system or photoevaporation processes open a gap in the inner disk, drastically changing the disk structure. From theoretical arguments it is expected that dust growth, fragmentation and radial drift are strongly influenced by gas disk structure, and pressure bumps in disks have been suggested as key features that may allow grains to converge and grow efficiently.Aims. We want to study how the presence of a large planet in a disk influences the growth and radial distribution of dust grains, and how observable properties are linked to the mass of the planet.Methods. We combined two-dimensional hydrodynamical disk simulations of disk-planet interactions with state-of-the-art coagulation/fragmentation models to simulate the evolution of dust in a disk, which has a gap created by a massive planet. We computed images at different wavelengths and illustrated our results using the example of the transition disk LkCa15.Results. The gap opened by a planet and the long-range interaction between the planet and the outer disk create a single large pressure bump outside the planetary orbit. Millimeter-sized particles form and accumulate at the pressure maximum and naturally produce ring-shaped sub-millimeter emission that is long-lived because radial drift no longer depletes the large grain population of the disk. For large planet masses around 9 M Jup , the pressure maximum and, therefore, the ring of millimeter particles is located at distances that can be more than twice the star-planet separation, creating a large spatial separation between the gas inner edge of the outer disk and the peak millimeter emission. Smaller grains do get closer to the gap and we predict how the surface brightness varies at different wavelengths.
444 citations
Cites background from "A dual-frequency sub-arcsecond stud..."
...The same physical process happens to the millimeter-size particles that are observed in the outer regions of the disk (e.g., Wilner et al. 2000; Ricci et al. 2010; Guilloteau et al. 2011)....
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2,538 citations
"A dual-frequency sub-arcsecond stud..." refers methods in this paper
...…model The shape of the surface density profile used in Model 2 corresponds to the self-similar solution of the viscous evolution of a A105, page 25 of 41 disk under the assumption that the viscosity is constant in time and a power law of radius (see Lynden-Bell & Pringle 1974; Pringle 1981)....
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...In the framework of self-similar viscous evolution (Lynden-Bell & Pringle 1974; Hartmann et al. 1998), it can be shown that Rt is the radius at which the net mass flux changes sign....
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TL;DR: In this paper, the authors proposed a method of redistributing angular momentum among the gas particles in order to let some of them fall into the potential well, then they are in a position to extract the potential energy so released.
Abstract: If we put a particle in a circular orbit around a central gravitating body, it will stay in that orbit. If we then extract energy and angular momentum from the particle we may allow it to spiral slowly inwards. The amount of energy that can be extracted by such a process is equal to the binding energy of the innermost accessible orbit. For orbits around sufficiently compact objects a reasonable fraction of the particle's rest mass energy can be extracted. For example, of order 10 percent of the rest mass can be obtained from orbits around a neutron star and up to around 40 percent for orbits around a black hole. Thus, the accretion process can be an effi cient converter of rest mass to radiation. The problem is to set up the process that can extract the energy and angular momentum. If we consider a blob of gas in a circular orbit then we have more flexibility. In particular, if we can find a method of redistributing angular momentum among the gas particles in order to let some of them fall into the potential well, then we are in a position to extract the potential energy so released. The accretion disc provides just such a method. The efficiency with which energy is released and the ubiquity of angular momentum explains why accretion discs are popular in models for some of the most luminous objects-X-ray stars and quasars. However, accretion disc theory predates the discovery of both these, and it is to these initial developments that we now tum our attention.
2,051 citations
"A dual-frequency sub-arcsecond stud..." refers methods in this paper
...…model The shape of the surface density profile used in Model 2 corresponds to the self-similar solution of the viscous evolution of a A105, page 25 of 41 disk under the assumption that the viscosity is constant in time and a power law of radius (see Lynden-Bell & Pringle 1974; Pringle 1981)....
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2,001 citations
"A dual-frequency sub-arcsecond stud..." refers background in this paper
...Indeed, only small dust grains are efficiently coupled to the gas, while the larger ones should drift quickly inward (e.g. Weidenschilling 1977)....
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2,001 citations
1,928 citations
"A dual-frequency sub-arcsecond stud..." refers methods in this paper
...In our sample, only the youngest objects have sufficiently high surface densities to be compatible with the MMSN....
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...Figure 12 also displays the profiles derived for the Solar Nebula, the MMSN (Hayashi 1981, gray line) and the solution proposed by Desch (2007), which accounts for the early planet migration as proposed by the Nice model (Tsiganis et al. 2005; Gomes et al. 2005) (yellow range)....
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