Volatile Depletion in the Tw Hydrae Disk Atmosphere

Du, Fujun; Bergin, Edwin A.; Hogerheijde, M. R.

doi:10.1088/2041-8205/807/2/l32

Cited by 104 publications

(164 citation statements)

References 47 publications

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“…Based on C 18 O emission and the HD gas mass, an elemental gas-phase carbon and oxygen deficiency of a factor of 10-100 was already inferred for this disk Bergin et al 2013;Favre et al 2013;Du et al 2015). Our models confirm these results.…”

Section: Tw Hya: Carbon and Oxygen Are Underabundantsupporting

confidence: 84%

“…It is possible that grain growth provides an additional efficiency boost to the volatile loss process, by trapping some of the ices formed on small, coupled grains in larger particles via coagulation before the small grains can be mixed back to the disk surface (Du et al 2015). The timescales of dust growth and vertical mixing are similar, within an order of magnitude, and their competition is not yet well observationally constrained.…”

Section: An Analytical Model Of Volatile Lockingmentioning

confidence: 99%

“…This is generally understood to result from the freeze-out of molecules in the midplane and from CO photodissociation in the disk atmosphere (Dutrey et al 1996(Dutrey et al , 1997(Dutrey et al , 2003van Zadelhoff et al 2001;Chapillon et al 2008Chapillon et al , 2010. Studies that account for these processes have suggested that the gas is genuinely underabundant in carbon in the disks around HD 100546 and TW Hya (Bruderer et al 2012;Bergin et al 2013;Favre et al 2013;Du et al 2015). We revisit the gas-phase carbon abundance in these disks, including new detections of far-infrared [C i] lines in the analysis, and present an analytical model for describing the volatile loss.…”

Section: Introductionmentioning

confidence: 99%

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Volatile-carbon locking and release in protoplanetary disks

Kama

Bruderer

Dishoeck

et al. 2016

A&A

203

312

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Aims. The composition of planetary solids and gases is largely rooted in the processing of volatile elements in protoplanetary disks. To shed light on the key processes, we carry out a comparative analysis of the gas-phase carbon abundance in two systems with a similar age and disk mass, but different central stars: HD 100546 and TW Hya. Methods. We combine our recent detections of C 0 in these disks with observations of other carbon reservoirs (CO, C + , C 2 H) and gas-mass and warm-gas tracers (HD, O 0 ), as well as spatially resolved ALMA observations and the spectral energy distribution. The disks are modelled with the DALI 2D physical-chemical code. Stellar abundances for HD 100546 are derived from archival spectra. Results. Upper limits on HD emission from HD 100546 place an upper limit on the total disk mass of ≤0.1 M . The gas-phase carbon abundance in the atmosphere of this warm Herbig disk is, at most, moderately depleted compared to the interstellar medium, with [C]/[H] gas = (0.1−1.5) × 10 −4 . HD 100546 itself is a λ Boötis star, with solar abundances of C and O but a strong depletion of rockforming elements. In the gas of the T Tauri disk TW Hya, both C and O are strongly underabundant, with [C]/[H] gas = (0.2−5.0)×10 −6 and C/O > 1. We discuss evidence that the gas-phase C and O abundances are high in the warm inner regions of both disks. Our analytical model, including vertical mixing and a grain size distribution, reproduces the observed [C]/[H] gas in the outer disk of TW Hya and allows to make predictions for other systems.

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Section: Tw Hya: Carbon and Oxygen Are Underabundantsupporting

confidence: 84%

Section: An Analytical Model Of Volatile Lockingmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Volatile-carbon locking and release in protoplanetary disks

Kama

Bruderer

Dishoeck

et al. 2016

A&A

203

312

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“…-the destruction of CO by He + and the subsequent conversion of atomic carbon to more complex carbon bearing molecules with higher freeze-out temperatures (Aikawa et al 1996;Bergin et al 2014;Helling et al 2014;Furuya & Aikawa 2014), -depletion of CO in layers above the CO ice line (up to T ≈ 30 K) due to conversion of CO to CO 2 on the surfaces of dust grains (Reboussin et al 2015), -CO isotopologue selective photodissociation, which affects CO isotopologue line emission and therefore the derived CO depletion factors, -carbon and/or oxygen depletion in the warm disk atmosphere due to settling and mixing of ice coated dust grains (Du et al 2015;Kama et al 2016b). …”

Section: Co Depletionmentioning

confidence: 99%

Stellar energetic particle ionization in protoplanetary disks around T Tauri stars

Rab

Güdel

Padovani

et al. 2017

A&A

102

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Context. Anomalies in the abundance measurements of short lived radionuclides in meteorites indicate that the protosolar nebulae was irradiated by a high amount of energetic particles (E 10 MeV). The particle flux of the contemporary Sun cannot explain these anomalies. However, similar to T Tauri stars the young Sun was more active and probably produced enough high energy particles to explain those anomalies. Aims. We want to study the interaction of stellar energetic particles with the gas component of the disk (i.e. ionization of molecular hydrogen) and identify possible observational tracers of this interaction. Methods. We use a 2D radiation thermo-chemical protoplanetary disk code to model a disk representative for T Tauri stars. We use a particle energy distribution derived from solar flare observations and an enhanced stellar particle flux proposed for T Tauri stars. For this particle spectrum we calculate the stellar particle ionization rate throughout the disk with an accurate particle transport model. We study the impact of stellar particles for models with varying X-ray and cosmic-ray ionization rates. Results. We find that stellar particle ionization has a significant impact on the abundances of the common disk ionization tracers HCO + and N 2 H + , especially in models with low cosmic-ray ionization rates (e.g. 10 −19 s −1 for molecular hydrogen). In contrast to cosmic rays and X-rays, stellar particles cannot reach the midplane of the disk. Therefore molecular ions residing in the disk surface layers are more affected by stellar particle ionization than molecular ions tracing the cold layers/midplane of the disk. Conclusions. Spatially resolved observations of molecular ions tracing different vertical layers of the disk allow to disentangle the contribution of stellar particle ionization from other competing ionization sources. Modeling such observations with a model like the one presented here allows to constrain the stellar particle flux in disks around T Tauri stars.

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“…However, studies that include these effects find that overall gas phase carbon must still be additionally depleted by a factor 10- 100. This leads to low CO emission even for massive disks (e.g., Bruderer et al 2012;Favre et al 2013;Du et al 2015;Kama et al 2016b;Bergin et al 2016).…”

Section: Introductionmentioning

confidence: 99%

Far-infrared HD emission as a measure of protoplanetary disk mass

Trapman

Miotello

Kama

et al. 2017

A&A

101

138

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Context. Protoplanetary disks around young stars are the sites of planet formation. While the dust mass can be estimated using standard methods, determining the gas mass -and thus the amount of material available to form giant planets -has proven to be very difficult. Hydrogen deuteride (HD) is a promising alternative to the commonly-used gas mass tracer, carbon monoxide. However, its potential has not yet been investigated with models incorporating both HD and CO isotopologue-specific chemistry, and its sensitivity to uncertainties in disk parameters has not yet been quantified. Aims. To examine the robustness of HD as tracer of the disk gas mass, specifically the effect of gas mass on the HD far infrared emission and its sensitivity to the vertical structure. Also, to provide requirements for future far-infrared missions such as SPICA. Methods. Deuterium chemistry reactions relevant for HD were implemented in the thermochemical code DALI and more than 160 disk models were run for a range of disk masses and vertical structures. Results. The HD J=1-0 line intensity depends directly on the gas mass through a sublinear power law relation with a slope of ∼0.8. Assuming no prior knowledge about the vertical structure of a disk and using only the HD 1-0 flux, gas masses can be estimated to within a factor of two for low mass disks (M disk ≤ 10 −3 M ). For more massive disks, this uncertainty increases to more than an order of magnitude. Adding the HD 2-1 line or independent information about the vertical structure can reduce this uncertainty to a factor of ∼ 3 for all disk masses. For TW Hya, using the radial and vertical structure from Kama et al. (2016b) the observations constrain the gas mass to 6 · 10 −3 M ≤ M disk ≤ 9 · 10 −3 M . Future observations require a 5σ sensitivity of 1.8 · 10 −20 W m −2 (2.5 · 10 −20 W m −2 ) and a spectral resolving power R ≥ 300 (1000) to detect HD 1-0 (HD 2-1) for all disk masses above 10 −5 M with a line-to-continuum ratio ≥ 0.01. Conclusions. These results show that HD can be used as an independent gas mass tracer with a relatively low uncertainty and should be considered as an important science goal for future far-infrared missions.

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Volatile Depletion in the Tw Hydrae Disk Atmosphere

Cited by 104 publications

References 47 publications

Volatile-carbon locking and release in protoplanetary disks

Volatile-carbon locking and release in protoplanetary disks

Stellar energetic particle ionization in protoplanetary disks around T Tauri stars

Far-infrared HD emission as a measure of protoplanetary disk mass

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