Reduction of chemical networks

Semenov, D.; Wiebe, D. S.; Henning, Th.

doi:10.1051/0004-6361:20034128

Cited by 143 publications

(177 citation statements)

References 39 publications

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“…X-ray irradiation, which is not yet included in the DENT grid, can also contribute significantly to the gas heating and chemistry for low-mass objects (e.g. Glassgold et al 2004;Semenov et al 2004;Meijerink et al 2008;Hollenbach & Gorti 2009;Ercolano & Owen 2010) and higher fluxes can be expected for sources with typical T Tauri X-ray emission. The small number of sources observed by GASPS so far prevents us from distinguishing between UV and X-rays for the main heating process for low mass objects.…”

Section: Resultsmentioning

confidence: 99%

TheHerschelview of GAS in Protoplanetary Systems (GASPS)

Pinte

Woitke²,

Ménard³

et al. 2010

A&A

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The Herschel GASPS key program is a survey of the gas phase of protoplanetary discs, targeting 240 objects which cover a large range of ages, spectral types, and disc properties. To interpret this large quantity of data and initiate self-consistent analyses of the gas and dust properties of protoplanetary discs, we have combined the capabilities of the radiative transfer code MCFOST with the gas thermal balance and chemistry code ProDiMo to compute a grid of ≈300 000 disc models (DENT). We present a comparison of the first Herschel/GASPS line and continuum data with the predictions from the DENT grid of models. Our objective is to test some of the main trends already identified in the DENT grid, as well as to define better empirical diagnostics to estimate the total gas mass of protoplanetary discs. Photospheric UV radiation appears to be the dominant gas-heating mechanism for Herbig stars, whereas UV excess and/or X-rays emission dominates for T Tauri stars. The DENT grid reveals the complexity in the analysis of far-IR lines and the difficulty to invert these observations into physical quantities. The combination of Herschel line observations with continuum data and/or with rotational lines in the (sub-)millimetre regime, in particular CO lines, is required for a detailed characterisation of the physical and chemical properties of circumstellar discs.

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Section: Resultsmentioning

confidence: 99%

TheHerschelview of GAS in Protoplanetary Systems (GASPS)

Pinte

Woitke²,

Ménard³

et al. 2010

A&A

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“…We, nevertheless, find that only when adopting C/O ratios substantially lower than the solar value (0.54; Asplund et al 2005) do the abundances of C-bearing species decrease appreciably. The choice of the initial abundances is also an issue when modeling the chemistry in protoplanetary disks and several options have been used in the literature (see, e.g., Willacy et al 1998;Semenov et al 2004). If we assume an initial atomic composition, instead of a molecular one, we find that the chemical timescale is noticeably reduced (the step i has been already carried out) although the steady state abundance is essentially the same.…”

Section: Chemical Routes To C 2 H 2 Hcn and Chmentioning

confidence: 99%

Formation of simple organic molecules in inner T Tauri disks

Agúndez¹,

Cernicharo²,

Goicoechea³

2008

A&A

155

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Aims. We present time dependent chemical models for a dense and warm O-rich gas exposed to a strong, far ultraviolet (FUV) field aimed at exploring the formation of simple organic molecules in the inner regions of protoplanetary disks around T Tauri stars.Methods. An up-to-date chemical network is used to compute the evolution of molecular abundances. Reactions of H 2 with small organic radicals such as C 2 and C 2 H, which are not included in current astrochemical databases, overcome their moderate activation energies at warm temperatures and become very important for the gas phase synthesis of C-bearing molecules.Results. The photodissociation of CO and release of C triggers the formation of simple organic species such as C 2 H 2 , HCN, and CH 4 . In timescales between 1 and 10 4 years, depending on the density and FUV field, a steady state is reached in the model in which molecules are continuously photodissociated, but also formed, mainly through gas phase chemical reactions involving H 2 . Conclusions. The application of the model to the upper layers of inner protoplanetary disks predicts large gas phase abundances of C 2 H 2 and HCN. The implied vertical column densities are as large as several 10 16 cm −2 in the very inner disk (<1 AU), in good agreement with the recent infrared observations of warm C 2 H 2 and HCN in the inner regions of IRS 46 and GV Tau disks. We also compare our results with previous chemical models studying the photoprocessing in the outer disk regions, and find that the gas phase chemical composition in the upper layers of the inner terrestrial zone (a few AU) is predicted to be substantially different from that in the upper layers of the outer disk (>50 AU).

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“…For example, Igea & Glassgold (1999), Article published by EDP Sciences Glassgold et al (2004) or Ercolano et al (2008) computed detailed models for radial distances between 0.5−10 AU that indicate efficient ionization of circumstellar disks by X-rays and also heating of the gaseous surface layers to several thousands of Kelvin. Complicated chemical networks are a consequence (e.g., Semenov et al 2004;or Ilgner & Nelson 2006). Direct evidence for these processes is suggested from the presence of strong line radiation of [Ne ii] at 12.8 μm detected by spitzer in many T Tauri stars (e.g., Pascucci et al 2007;Herczeg et al 2007;or Lahuis et al 2007) which in some cases may be triggered by shocks (van Boekel et al 2009).…”

Section: Introductionmentioning

confidence: 99%

Dust amorphization in protoplanetary disks

Glauser

Güdel

Watson

et al. 2009

A&A

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Aims. High-energy irradiation of circumstellar material might impact the structure and the composition of a protoplanetary disk and hence the process of planet formation. In this paper, we present a study of the possible influence of stellar irradiation, indicated by X-ray emission, on the crystalline structure of circumstellar dust. Methods. The dust crystallinity is measured for 42 class II T Tauri stars in the Taurus star-forming region using a decomposition fit of the 10 μm silicate feature, measured with the spitzer IRS instrument. Since the sample includes objects with disks of various evolutionary stages, we further confine the target selection, using the age of the objects as a selection parameter. Results. We correlate the X-ray luminosity and the X-ray hardness of the central object with the crystalline mass fraction of the circumstellar dust and find a significant anti-correlation for 20 objects within an age range of approx. 1 to 4.5 Myr. We postulate that X-rays represent the stellar activity and consequently the energetic ions of the stellar winds which interact with the circumstellar disk. We show that the fluxes around 1 AU and ion energies of the present solar wind are sufficient to amorphize the upper layer of dust grains very efficiently, leading to an observable reduction of the crystalline mass fraction of the circumstellar, sub-micron sized dust. This effect could also erase other relations between crystallinity and disk/star parameters such as age or spectral type.

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Reduction of chemical networks

Cited by 143 publications

References 39 publications

TheHerschelview of GAS in Protoplanetary Systems (GASPS)

TheHerschelview of GAS in Protoplanetary Systems (GASPS)

Formation of simple organic molecules in inner T Tauri disks

Dust amorphization in protoplanetary disks

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