scholarly journals Midplane temperature and outer edge of the protoplanetary disk around HD 163296

2020 ◽  
Vol 633 ◽  
pp. A137 ◽  
Author(s):  
C. P. Dullemond ◽  
A. Isella ◽  
S. M. Andrews ◽  
I. Skobleva ◽  
N. Dzyurkevich
Keyword(s):  
Direct Measurement ◽  
Direct Evidence ◽  
Protoplanetary Disks ◽  
Outer Edge ◽  
Dust Grains ◽  
Gas Temperature ◽  
Molecular Line ◽  
Model Assumption ◽  
Complex Models ◽  
Freeze Out

Knowledge of the midplane temperature of protoplanetary disks is one of the key ingredients in theories of dust growth and planet formation. However, direct measurement of this quantity is complicated, and often depends on the fitting of complex models to data. In this paper we demonstrate a method to directly measure the midplane gas temperature from an optically thick molecular line if the disk is moderately inclined. The only model assumption that enters is that the line is very optically thick, specifically in the midplane region where we wish to measure the temperature. Freeze-out of the molecule onto dust grains could thwart this. However, in regions that are expected to be warm enough to avoid freeze-out, this method should work. We apply the method to the CO 2–1 line channel maps of the disk around HD 163296. We find that the midplane temperature between 100 and 400 au drops only mildly from 25 K down to 18 K. While we see no direct evidence of the midplane being optically thin due to strong CO depletion by freeze-out, we cannot rule it out either. The fact that the inferred temperatures are close to the expected CO freeze-out temperature could be an indication of this. Incidently, for the disk around HD 163296 we also find dynamic evidence for a rather abrupt outer edge of the disk, suggestive of outside-in photoevaporation or truncation by an unseen companion.

scholarly journals Constraining protoplanetary disk accretion and young planets using ALMA kinematic observations

2021 ◽  
Author(s):  
Ian Rabago ◽  
Zhaohuan Zhu
Keyword(s):  
Velocity Structure ◽  
Protoplanetary Disks ◽  
Disk Surface ◽  
Outer Edge ◽  
Disk Accretion ◽  
Gas Velocity ◽  
Molecular Line ◽  
Stress Profiles ◽  
The Relationship ◽  
Disk Height

Abstract Recent ALMA molecular line observations have revealed 3-D gas velocity structure in protoplanetary disks, shedding light on mechanisms of disk accretion and structure formation. 1) By carrying out viscous simulations, we confirm that the disk’s velocity structure differs dramatically using vertical stress profiles from different accretion mechanisms. Thus, kinematic observations tracing flows at different disk heights can potentially distinguish different accretion mechanisms. On the other hand, the disk surface density evolution is mostly determined by the vertically integrated stress. The sharp disk outer edge constrained by recent kinematic observations can be caused by a radially varying α in the disk. 2) We also study kinematic signatures of a young planet by carrying out 3-D planet-disk simulations. The relationship between the planet mass and the ‘kink’ velocity is derived, showing a linear relationship with little dependence on disk viscosity, but some dependence on disk height when the planet is massive (e.g. 10MJ). We predict the ‘kink’ velocities for the potential planets in DSHARP disks. At the gap edge, the azimuthally-averaged velocities at different disk heights deviate from the Keplerian velocity at similar amplitudes, and its relationship with the planet mass is consistent with that in 2-D simulations. After removing the planet, the azimuthally-averaged velocity barely changes within the viscous timescale, and thus the azimuthally-averaged velocity structure at the gap edge is due to the gap itself and not directly caused to the planet. Combining both axisymmetric kinematic observations and the residual ‘kink’ velocity is needed to probe young planets in protoplanetary disks.

scholarly journals Rapid elimination of small dust grains in molecular clouds

2020 ◽  
Vol 641 ◽  
pp. A39 ◽  
Author(s):  
Kedron Silsbee ◽  
Alexei V. Ivlev ◽  
Olli Sipilä ◽  
Paola Caselli ◽  
Bo Zhao
Keyword(s):  
Size Distribution ◽  
Cosmic Ray ◽  
Ionization Rate ◽  
Microwave Emission ◽  
Dust Grains ◽  
Gas Temperature ◽  
Neutral Gas ◽  
Cloud Cores ◽  
The Impact ◽  
Small Dust

We argue that impact velocities between dust grains with sizes of less than ∼0.1 μm in molecular cloud cores are dominated by drift arising from ambipolar diffusion. This effect is due to the size dependence of the dust coupling to the magnetic field and the neutral gas. Assuming perfect sticking in collisions up to ≈50 m s−1, we show that this effect causes rapid depletion of small grains, consistent with starlight extinction and IR and microwave emission measurements, both in the core center (n ∼ 106 cm−3) and envelope (n ∼ 104 cm−3). The upper end of the size distribution does not change significantly if only velocities arising from this effect are considered. We consider the impact of an evolved grain-size distribution on the gas temperature, and argue that if the depletion of small dust grains occurs as expected from our model, then the cosmic ray ionization rate must be well below 10−16 s−1 at a number density of 105 cm−3.

scholarly journals Thermal evolution of protoplanetary disks: from β-cooling to decoupled gas and dust temperatures

2020 ◽  
Vol 638 ◽  
pp. A102 ◽  
Author(s):  
Eduard I. Vorobyov ◽  
Ryoki Matsukoba ◽  
Kazuyuki Omukai ◽  
Manuel Guedel
Keyword(s):  
Thermal Evolution ◽  
Thermal Structure ◽  
Protoplanetary Disks ◽  
Gas Temperature ◽  
Numerical Hydrodynamics ◽  
Variable Nature ◽  
Dynamical Time ◽  
Envelope Material ◽  
Disk Evolution ◽  
Dust Evolution

Aims. We explore the long-term evolution of young protoplanetary disks with different approaches to computing the thermal structure determined by various cooling and heating processes in the disk and its surroundings. Methods. Numerical hydrodynamics simulations in the thin-disk limit were complemented with three thermal evolution schemes: a simplified β-cooling approach with and without irradiation, where the rate of disk cooling is proportional to the local dynamical time; a fiducial model with equal dust and gas temperatures calculated taking viscous heating, irradiation, and radiative cooling into account; and a more sophisticated approach allowing decoupled dust and gas temperatures. Results. We found that the gas temperature may significantly exceed that of dust in the outer regions of young disks thanks to additional compressional heating caused by the infalling envelope material in the early stages of disk evolution and slow collisional exchange of energy between gas and dust in low-density disk regions. However, the outer envelope shows an inverse trend, with the gas temperatures dropping below that of dust. The global disk evolution is only weakly sensitive to temperature decoupling. Nevertheless, separate dust and gas temperatures may affect the chemical composition, dust evolution, and disk mass estimates. Constant-β models without stellar and background irradiation fail to reproduce the disk evolution with more sophisticated thermal schemes because of the intrinsically variable nature of the β-parameter. Constant-β models with irradiation more closely match the dynamical and thermal evolution, but the agreement is still incomplete. Conclusions. Models allowing separate dust and gas temperatures are needed when emphasis is placed on the chemical or dust evolution in protoplanetary disks, particularly in subsolar metallicity environments.

scholarly journals Molecules with ALMA at Planet-forming Scales (MAPS). II. CLEAN Strategies for Synthesizing Images of Molecular Line Emission in Protoplanetary Disks

2021 ◽  
Vol 257 (1) ◽  
pp. 2 ◽  
Author(s):  
Ian Czekala ◽  
Ryan A. Loomis ◽  
Richard Teague ◽  
Alice S. Booth ◽  
Jane Huang ◽  
...  
Keyword(s):  
Line Emission ◽  
Protoplanetary Disks ◽  
Molecular Line

scholarly journals Gas vs dust radial extent in disks: the importance of their thermal interplay

2017 ◽  
Vol 13 (S332) ◽  
pp. 129-136
Author(s):  
Stefano Facchini
Keyword(s):  
Thermal Structure ◽  
Sharp Decrease ◽  
Outer Edge ◽  
Outer Radius ◽  
Gas Temperature ◽  
Secular Evolution ◽  
Radial Extent ◽  
Grain Size Distributions ◽  
The Difference ◽  
Dust Grain

AbstractA key parameter governing the secular evolution of protoplanetary disks is their outer radius. In this paper, the feedback of realistic dust grain size distributions onto the gas emission is investigated. Models predict that the difference of dust and gas extents as traced by CO is primarily caused by differences in the optical depth of lines vs continuum. The main effect of radial drift is the sharp decrease in the intensity profile at the outer edge. The gas radial extent can easily range within a factor of 2 for models with different turbulence. A combination of grain growth and vertical settling leads to thermal de-coupling between gas and dust at intermediate scale-heights. A proper treatment of the gas thermal structure within dust gaps will be fundamental to disentangle surface density gaps from gas temperature gaps.

scholarly journals The Gas Temperature in the Surface Layers of Protoplanetary Disks

2004 ◽  
Vol 615 (2) ◽  
pp. 991-999 ◽  
Author(s):  
I. Kamp ◽  
C. P. Dullemond
Keyword(s):  
Protoplanetary Disks ◽  
Gas Temperature ◽  
Surface Layers
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