X‐Ray Ionization of the Disks of Young Stellar Objects

Igea, J.; Glassgold, A. E.

doi:10.1086/307302

Cited by 289 publications

(371 citation statements)

References 45 publications

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“…For photon energy ε, integration is over the cross section σ k starting at the ionization edge ε k for the considered species k. The sum is over all possible species. Numerical evaluation of these expressions for a realistic disk profile were performed by Glassgold et al (1997); Igea & Glassgold (1999) improved these calculations for more realistic disk shapes and consideration of Compton scattering of energetic X-rays. The results can be summarized as follows (see Fig.…”

Section: X-ray and Cr Ionization And The Magnetorotational Instabilitymentioning

confidence: 99%

“…The source X-ray luminosity has been normalized to 1 erg s −1 . The shoulder at deep levels are due to Compton scattering (from Igea & Glassgold 1999). -Right: Electron fraction in a disk due to X-ray ionization, shown in the radius -N ⊥ (vertical column density) plane.…”

Section: Summer School "Protoplanetary Disks: Theory and Modeling Meementioning

confidence: 99%

“…"Critical surface" marks the height below which the ionization fraction is too low to induce the magnetorotational instability. The solid lines give disk mid-planes from different models (from Igea & Glassgold 1999; c AAS. Reproduced with permission).…”

Section: Summer School "Protoplanetary Disks: Theory and Modeling Meementioning

confidence: 99%

“…Various assumptions can be made to solve this equation for n(e). For a purely molecular gas, we may neglect terms with M and keep only the first and the third term, from which we find for the electron fraction x e = n e /n x e = ζ X nα 1/2 (63) where, in a realistic situation for protoplanetary disks, α ≈ 2 × 10 −6 T −1/2 cm 3 s −1 and n is the hydrogen number density (Glassgold et al 1997;Igea & Glassgold 1999). Calculations by Glassgold et al (1997) and Igea & Glassgold (1999) show (accounting for sedimentation of condensible heavy elements) that n(e) decreases rapidly toward the disk midplane; for a given vertical column density N ⊥ , n(e) decreases with distance r; together, the disk ionization structure is stratified in such a way that a given ionization fraction defines a wedge-shaped region around the inner disk mid-plane with its apex at the mid-plane at some outer radius (Fig.…”

Section: Summer School "Protoplanetary Disks: Theory and Modeling Meementioning

confidence: 99%

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Ionization and heating by X-rays and cosmic rays

Güdel

2015

EPJ Web of Conferences

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Abstract. High-energy radiation from the central T Tauri and protostars plays an important role in shaping protoplanetary disks and influences their evolution. Such radiation, in particular X-rays and extreme-ultraviolet (EUV) radiation, is predominantly generated in unstable stellar magnetic fields (e.g., the stellar corona), but also in accretion hot spots. Even jets may produce X-ray emission. Cosmic rays, i.e., high-energy particles either from the interstellar space or from the star itself, are of crucial importance. Both highenergy photons and particles ionize disk gas and lead to heating. Ionization and heating subsequently drive chemical networks, and the products of these processes are accessible through observations of molecular line emission. Furthermore, ionization supports the magnetorotational instability and therefore drives disk accretion, while heating of the disk surface layers induces photoevaporative flows. Both processes are crucial for the dispersal of protoplanetary disks and therefore critical for the time scales of planet formation. This chapter introduces the basic physics of ionization and heating starting from a quantum mechanical viewpoint, then discusses relevant processes in astrophysical gases and their applications to protoplanetary disks, and finally summarizes some properties of the most important high-energy sources for protoplanetary disks.

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Section: X-ray and Cr Ionization And The Magnetorotational Instabilitymentioning

confidence: 99%

Section: Summer School "Protoplanetary Disks: Theory and Modeling Meementioning

confidence: 99%

Section: Summer School "Protoplanetary Disks: Theory and Modeling Meementioning

confidence: 99%

Section: Summer School "Protoplanetary Disks: Theory and Modeling Meementioning

confidence: 99%

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Ionization and heating by X-rays and cosmic rays

Güdel

2015

EPJ Web of Conferences

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“…The main effect of X-rays on the chemistry is the ionization of the gas producing high-energy photoelectrons (ph-e − ), which further ionize and dissociate the species. To simulate this effect we have enhanced the cosmic ray ionization rate by a factor of 1000 over the standard interstellar value, we thus assume ζ = 1.2 × 10 −14 s −1 , which is reasonable for the inner regions of PPDs (Igea & Glassgold 1999).…”

Section: Chemical Modelmentioning

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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Chemistry of Protoplanetary Disks

Markwickan¹,

Charnley²

2004

Astrobiology: Future Perspectives

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X‐Ray Ionization of the Disks of Young Stellar Objects

Cited by 289 publications

References 45 publications

Ionization and heating by X-rays and cosmic rays

Ionization and heating by X-rays and cosmic rays

Formation of simple organic molecules in inner T Tauri disks

Chemistry of Protoplanetary Disks

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