Turbulent linewidths as a diagnostic of self-gravity in protostellar discs

Forgan, Duncan; Armitage, Philip J.; Simon, Jacob B.

doi:10.1111/j.1365-2966.2012.21962.x

Cited by 17 publications

(23 citation statements)

References 52 publications

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“…In both cases, the dominant motion of the compact flattened structure during the embedded phase is infall rather than rotation. There are indeed sources where higher sensitivity and spatial resolution observations such as with Atacama Large Millimeter/submillimeter Array (ALMA) can detect features associated with disk instabilities (e.g., Cossins et al 2010;Forgan et al 2012;Douglas et al 2013). …”

Section: Disk Stabilitymentioning

confidence: 99%

Rotationally-supported disks around Class I sources in Taurus: disk formation constraints

Harsono

Jørgensen

Dishoeck

et al. 2014

A&A

128

169

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Context. Disks are observed around pre-main sequence stars, but how and when they form is still heavily debated. While disks around young stellar objects have been identified through thermal dust emission, spatially and spectrally resolved molecular line observations are needed to determine their nature. Only a handful of embedded rotationally supported disks have been identified to date. Aims. We identify and characterize rotationally supported disks near the end of the main accretion phase of low-mass protostars by comparing their gas and dust structures. Methods. Subarcsecond observations of dust and gas toward four Class I low-mass young stellar objects in Taurus are presented at significantly higher sensitivity than previous studies. The 13 CO and C 18 O J = 2-1 transitions at 220 GHz were observed with the Plateau de Bure Interferometer at a spatial resolution of ≤0.8 (56 AU radius at 140 pc) and analyzed using uv-space position velocity diagrams to determine the nature of their observed velocity gradient. Results. Rotationally supported disks (RSDs) are detected around 3 of the 4 Class I sources studied. The derived masses identify them as Stage I objects; i.e., their stellar mass is higher than their envelope and disk masses. The outer radii of the Keplerian disks toward our sample of Class I sources are ≤100 AU. The lack of on-source C 18 O emission for TMR1 puts an upper limit of 50 AU on its size. Flattened structures at radii >100 AU around these sources are dominated by infalling motion (υ ∝ r −1 ). A large-scale envelope model is required to estimate the basic parameters of the flattened structure from spatially resolved continuum data. Similarities and differences between the gas and dust disk are discussed. Combined with literature data, the sizes of the RSDs around Class I objects are best described with evolutionary models with an initial rotation of Ω = 10 −14 Hz and slow sound speeds. Based on the comparison of gas and dust disk masses, little CO is frozen out within 100 AU in these disks. Conclusions. Rotationally supported disks with radii up to 100 AU are present around Class I embedded objects. Larger surveys of both Class 0 and I objects are needed to determine whether most disks form late or early in the embedded phase.

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Section: Disk Stabilitymentioning

confidence: 99%

Rotationally-supported disks around Class I sources in Taurus: disk formation constraints

Harsono

Jørgensen

Dishoeck

et al. 2014

A&A

128

169

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“…We forego a full spectral line analysis and instead compute a line-of-sight (los) turbulent velocity in the disk plane, averaged over azimuth φ: (Simon et al 2011;Forgan et al 2012). Here we use δv y for the turbulent velocity in the azimuthal direction, not to be confused with the bulk velocity v y which includes the background shear velocity.…”

Section: Turbulent Velocities Versus Heightmentioning

confidence: 99%

“…M. Hughes et al 2014, in preparation). Similarly illuminating would be radial profiles of non-thermal linewidths (Forgan et al 2012); these are promised by, e.g., the Atacama Large Millimeter Array.…”

Section: Introductionmentioning

confidence: 99%

“…Recent studies explore a host of non-ideal magnetohydrodynamic effects that strongly affect the character of transport in poorly ionized disks (e.g., PerezBecker & Chiang 2011a, 2011bBai 2011;Wardle & Salmeron 2012;Bai & Stone 2013;Bai 2013;Simon et al 2013aSimon et al , 2013bKunz & Lesur 2013;Lesur et al 2014). Disk self-gravity is another option for sufficiently massive disks (e.g., Paczynski 1978;Gammie 2001;Forgan et al 2012). Torques could be exerted either by globally coherent spiral structure, or by local density waves that are continuously generated and dissipated in a state of "gravito-turbulence."…”

Section: Introductionmentioning

confidence: 99%

“…By determining what is distinctive about these vertical profiles, we hope to inform observations of non-thermal linewidths like those pioneered by Hughes et al (2011), and ultimately to characterize turbulence in disks, protoplanetary or otherwise. We utilize a grid-based code (Athena) to resolve stratified, self-gravitating, secularly cooling disks, achieving unprecedentedly high resolution and dynamic range in the vertical direction (see Forgan et al 2012). Radiative cooling is treated in the optically thin limit in which every grid cell cools independently of every other.…”

Section: Introductionmentioning

confidence: 99%

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Gravito-Turbulent Disks in Three Dimensions: Turbulent Velocities Versus Depth

Shi

Chiang

2014

ApJ

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Characterizing turbulence in protoplanetary disks is crucial for understanding how they accrete and spawn planets. Recent measurements of spectral line broadening promise to diagnose turbulence, with different lines probing different depths. We use three-dimensional local hydrodynamic simulations of cooling, self-gravitating disks to resolve how motions driven by "gravito-turbulence" vary with height. We find that gravito-turbulence is practically as vigorous at altitude as at depth. Even though gas at altitude is much too rarefied to be itself self-gravitating, it is strongly forced by self-gravitating overdensities at the midplane. The long-range nature of gravity means that turbulent velocities are nearly uniform vertically, increasing by just a factor of two from midplane to surface, even as the density ranges over nearly three orders of magnitude. The insensitivity of gravito-turbulence to height contrasts with the behavior of disks afflicted by the magnetorotational instability (MRI); in the latter case, noncircular velocities increase by at least a factor of 15 from midplane to surface, with various non-ideal effects only magnifying this factor. The distinct vertical profiles of gravito-turbulence versus MRI turbulence may be used in conjunction with measurements of non-thermal linewidths at various depths to identify the source of transport in protoplanetary disks.

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Radiation thermo-chemical models of protoplanetary disks

Thi

Lesur

Woitke

et al. 2019

A&A

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Context. Disks around pre-main-sequence stars evolve over time by turbulent viscous spreading. The main contender to explain the strength of the turbulence is the magnetorotational instability model, whose efficiency depends on the disk ionization fraction. Aims. Our aim is to compute self-consistently the chemistry including polycyclic aromatic hydrocarbon (PAH) charge chemistry, the grain charging, and an estimate of an effective value of the turbulence α parameter in order to find observational signatures of disk turbulence. Methods. We introduced PAH and grain charging physics and their interplay with other gas-phase reactions in the physico-chemical code PRODIMO. Non-ideal magnetohydrodynamics effects such as ohmic and ambipolar diffusion are parametrized to derive an effective value for the turbulent parameter αeff. We explored the effects of turbulence heating and line broadening on CO isotopologue submillimeter lines. Results. The spatial distribution of αeff depends on various unconstrained disk parameters such as the magnetic parameter βmag or the cosmic ray density distribution inside the protoplanetary disk s. The inner disk midplane shows the presence of the so-called dead zone where the turbulence is almost inexistent. The disk is heated mostly by thermal accommodation on dust grains in the dead zone, by viscous heating outside the dead zone up to a few hundred astronomical units, and by chemical heating in the outer disk. The CO rotational lines probe the warm molecular disk layers where the turbulence is at its maximum. However, the effect of turbulence on the CO line profiles is minimal and difficult to distinguish from the thermal broadening. Conclusions. Viscous heating of the gas in the disk midplane outside the dead zone is efficient. The determination of α from CO rotational line observations alone is challenging.

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Turbulent linewidths as a diagnostic of self-gravity in protostellar discs

Cited by 17 publications

References 52 publications

Rotationally-supported disks around Class I sources in Taurus: disk formation constraints

Rotationally-supported disks around Class I sources in Taurus: disk formation constraints

Gravito-Turbulent Disks in Three Dimensions: Turbulent Velocities Versus Depth

Radiation thermo-chemical models of protoplanetary disks

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