Transport processes and chemical evolution  
in steady accretion disk flows

Ilgner, M.; Henning, Th.; Markwick, A. J.; Millar, T. J.

doi:10.1051/0004-6361:20034061

Cited by 75 publications

(82 citation statements)

References 36 publications

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“…shows that the cooling timescale in the disk is smaller than typical evolution timescales by orders of magnitude, and also smaller than typical mixing timescales (e.g. Ilgner et al 2004), justifying our assumption of thermal balance. In particular, the gas is thermally tightly coupled to the dust via thermal accommodation in the midplane regions where the cooling timescale scales as τ cool ≈ 1/ρ.…”

Section: Timescalessupporting

confidence: 73%

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Radiation thermo-chemical models of protoplanetary disks

Woitke

Kamp²,

Thi

2009

A&A

400

667

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Context. Emission lines from protoplanetary disks originate mainly in the irradiated surface layers, where the gas is generally warmer than the dust. Therefore, interpreting emission lines requires detailed thermo-chemical models, which are essential to converting line observations into understanding disk physics. Aims. We aim at hydrostatic disk models that are valid from 0.1 AU to 1000 AU to interpret gas emission lines from UV to sub-mm. In particular, our interest lies in interpreting far IR gas emission lines, such as will be observed by the Herschel observatory, related to the Gasps open time key program. This paper introduces a new disk code called ProDiMo. Methods. We combine frequency-dependent 2D dust continuum radiative transfer, kinetic gas-phase and UV photo-chemistry, ice formation, and detailed non-LTE heating & cooling with the consistent calculation of the hydrostatic disk structure. We include Fe ii and CO ro-vibrational line heating/cooling relevant to the high-density gas close to the star, and apply a modified escapeprobability treatment. The models are characterised by a high degree of consistency between the various physical, chemical, and radiative processes, where the mutual feedbacks are solved iteratively. Results. In application to a T Tauri disk extending from 0.5 AU to 500 AU, the models show that the dense, shielded and cold midplane (z/r < ∼ 0.1, T g ≈ T d ) is surrounded by a layer of hot (T g ≈ 5000 K) and thin (n H ≈ 10 7 to 10 8 cm −3 ) atomic gas that extends radially to about 10 AU and vertically up to z/r ≈ 0.5. This layer is predominantly heated by the stellar UV (e.g. PAH-heating) and cools via Fe ii semi-forbidden and Oi 630 nm optical line emission. The dust grains in this "halo" scatter the starlight back onto the disk, which affects the photochemistry. The more distant regions are characterised by a cooler flaring structure. Beyond r > ∼ 100 AU, T g decouples from T d even in the midplane and reaches values of about T g ≈ 2T d . Conclusions. Our models show that the gas energy balance is the key to understanding the vertical disk structure. Models calculated with the assumption T g = T d show a much flatter disk structure. The conditions in the close regions (<10 AU) with densities n H ≈ 10 8 to 10 15 cm −3 resemble those of cool stellar atmospheres and, thus, the heating and cooling is more like in stellar atmospheres. The application of heating and cooling rates known from PDR and interstellar cloud research alone can be misleading here, so more work needs to be invested to identify the leading heating and cooling processes.

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Section: Timescalessupporting

confidence: 73%

“…We find in particular two layers of hot and cold water molecules. Mixing by hydrodynamical motions is likely to smooth out such structures (Ilgner et al 2004;Semenov et al 2006;Tscharnuter & Gail 2007).…”

Section: Discussionmentioning

confidence: 99%

Radiation thermo-chemical models of protoplanetary disks

Woitke

Kamp²,

Thi

2009

A&A

400

667

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“…Protoplanetary disks are turbulent environments and the effects of vertical turbulent mixing on disk chemical structure has been investigated by multiple groups (see, e.g., Ilgner et al 2004;Willacy et al 2006;Semenov et al 2006;Aikawa 2007;Heinzeller et al 2011;Semenov & Wiebe 2011). Semenov & Wiebe (2011) conducted a comprehensive investigation of disk chemical structure with and without turbulent mixing and identified a plethora of species which are sensitive to mixing.…”

Section: Comparison With Other Modelsmentioning

confidence: 99%

Complex organic molecules in protoplanetary disks

Walsh

Millar

Nomura

et al. 2014

A&A

223

356

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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 H 2 CO observed towards T Tauri star-disk systems. There is poor agreement with HC 3 N lines observed towards LkCa 15 and GO Tau and we discuss possible explanations for these discrepancies. The synthesised line intensities for CH 3 OH are consistent with upper limits determined towards all sources. Our models suggest CH 3 OH 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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“…Finally, models of gas-phase chemistry including surface chemistry on grains are sensitive to the level of turbulent mixing (e.g. Ilgner et al 2004;Ilgner & Nelson 2006;Semenov & Wiebe 2011) which may partially explain the presence of cold CO in disks (Dartois et al 2003;Semenov et al 2006;Aikawa 2007;Hersant et al 2009).…”

Section: Introductionmentioning

confidence: 99%

Chemistry in disks

Guilloteau

Dutrey

Wakelam

et al. 2012

A&A

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Context. Turbulence is thought to be a key driver of the evolution of protoplanetary disks, regulating the mass accretion process, the transport of angular momentum, and the growth of dust particles. Aims. We intend to determine the magnitude of the turbulent motions in the outer parts (>100 AU) of the disk surrounding DM Tau. Methods. Turbulent motions can be constrained by measuring the nonthermal broadening of line emission from heavy molecules. We used the IRAM Plateau de Bure interferometer to study emission from the CS molecule in the disk of DM Tau. High spatial (1.4 × 1. ) and spectral resolution (0.126 km s −1 ) CS J = 3-2 images provide constraints on the molecule distribution and velocity structure of the disk. A low sensitivity CS J = 5-4 image was used in conjunction to evaluate the excitation conditions. We analyzed the data in terms of two parametric disk models, and compared the results with detailed time-dependent chemical simulations.Results. The CS data confirm the relatively low temperature suggested by observations of other simple molecules. The intrinsic linewidth derived from the CS J = 3-2 data is much larger than expected from pure thermal broadening. The magnitude of the derived nonthermal component depends only weakly on assumptions about the location of the CS molecules with respect to the disk plane. Our results indicate turbulence with a Mach number around 0.4-0.5 in the molecular layer. Geometrical constraints suggest that this layer is located near one scale height, in reasonable agreement with chemical model predictions.

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Transport processes and chemical evolution in steady accretion disk flows

Cited by 75 publications

References 36 publications

Radiation thermo-chemical models of protoplanetary disks

Radiation thermo-chemical models of protoplanetary disks

Complex organic molecules in protoplanetary disks

Chemistry in disks

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