The ionization fraction in α models of protoplanetary discs

By Sébastien Fromang, C. Terquem, Steven Balbus. 2001

220 citations recorded by the source corpus.

We calculate the ionization fraction of protostellar a discs, taking into account vertical temperature structure and the possible presence of trace metal atoms. Both thermal and X-ray ionization are considered. Previous investigations of layered discs used radial power-law models with isothermal vertical structure. But a models are used to model accretion, and the present work is a step towards a self-consistent treatment. The extent of the magnetically uncoupled ('dead') zone depends sensitively on a, on the assumed accretion rate and on the critical magnetic Reynolds number, below which magnetohydrodynamic (MHD) turbulence cannot be self-sustained. Its extent is extremely model-dependent. It is also shown that a tiny fraction of the cosmic abundance of metal atoms can dramatically affect the ionization balance. Gravitational instabilities are an unpromising source of transport, except in the early stages of disc formation.

Subfields: Astronomy and Astrophysics

View Paper: https://www.semanticscholar.org/paper/43ea2d174c8d8000f8681a7800687fe32627bad0

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Citations in the corpus

The Stellar Mass Spectrum from Non-Isothermal Gravoturbulent Fragmentation (2004, background): “This may lead to the formation of a binary or higher-order multiple (Bodenheimer et al. 2000; Fromang et al. 2002).”
Astrophysical magnetic fields and nonlinear dynamo theory (2004, unknown): “The ionization fraction at the ionization–recombination equilibrium is approximately given by xe=( / nn), where is the ionization 5 rate and = 3 × 10−6T −1/2 cm3 s−1 is the dissociative recombination rate [145,146].”
On the ionisation fraction in protoplanetary disks. I. Comparing different reaction networks (2005, methodology): “Fromang et al. (2002) considered the ionisation fraction in conventional α–disk models, and focussed on the role of heavy metals in a simple reaction network.”
Enhanced Angular Momentum Transport in Accretion Disks (2003, background): “It seems likely that there will be evolutionary phases when only the most distant (low density) and innermost (hot) gas will be magnetized, but it is also possible that an active X-ray source and agglomerated dust grains may render much of the disk magnetically well-coupled (Fromang et al. 2002).”
The Sun in Time: Activity and Environment (2007, background): “ and Glassgold 1999). These are the likely sites of planet formation (Glassgold et al., 1997). Modiﬁcations of these calculations by introducing trace heavy metals and diﬀusion have been discussed by Fromang et al. (2002) and Ilgner and Nelson (2006). Disk irradiation and photoionization by stellar ”
The physics of star formation (2003, background): “Even if a larger region around the central star could be kept sufficiently ionized by self-sustaining MHD turbulence, most of the mass in a protostellar disk would still be in a dead zone (Fromang et al 2002).”
EXCLUSION OF COSMIC RAYS IN PROTOPLANETARY DISKS: STELLAR AND MAGNETIC EFFECTS (2013, background): “We find that this assumption is acceptable as the bulk mass of the disk beyond R = 0.5 AU is well below the temperature threshold for thermal ionization (T >1000 K; Fromang et al. 2002).”
Gravoturbulent Formation of Planetesimals (2005, background): “Magnetorotational turbulence (MRI) on the other hand is expected to occur in all discs where the ionization fraction is sufficiently high (Gammie 1996; Fromang et al. 2002; Semenov et al. 2004).”
Thanatology in protoplanetary discs - The combined influence of Ohmic, Hall, and ambipolar diffusion on dead zones (2014, background): “S R ] 2 4 Fe b 20 14 2000; Fromang et al. 2002; Ilgner & Nelson 2006a,b) and threedimensional numerical simulations (Fleming et al. 2000; Fleming & Stone 2003; Turner et al. 2007; Ilgner & Nelson 2008).”
Global simulations of protoplanetary disks with net magnetic flux: I. Non-ideal MHD case (2016, background): “The total ionization rate is balanced by dissociative recombination, without dust grains nor metals (Fromang et al. 2002).”
Heating Protoplanetary Disk Atmospheres (2004, background): “This can occur if the surface layers are the only regions of the disk sufficiently ionized to participate in the MRI at small radii (Gammie 1996; G97; Fromang et al. 2002).”
Migration and the Formation of Systems of Hot Super-Earths and Neptunes (2006, background): “The studies done in the present paper assume that the cores can migrate down to the disk inner edge, in regions where the gas is ionized and magnetic turbulence can develop (Fromang et al. 2002).”
RESOLVED IMAGES OF LARGE CAVITIES IN PROTOPLANETARY TRANSITION DISKS (2011, background): “In a dense disk, the midplane can be so shielded from ionizing radiation that the MRI will not operate (Gammie 1996; Sano et al. 2000; Fromang et al. 2002): without that source of disruptive turbulence, particle growth can proceed more efficiently inside the dead zone.”
Dust settling in local simulations of turbulent protoplanetary disks (2006, background): “The extent of this dead zone is very uncertain, since it depends on the ionising source and on the chemistry (Sano et al. 2000; Fromang et al. 2002; Ilgner & Nelson 2006), but its existence is likely.”
Dead Zone Accretion Flows in Protostellar Disks (2008, background): “The region consists of a laminar resistive interior sandwiched between two conducting surface layers where magnetorotational turbulence causes an accretion flow (Gammie 1996; Sano et al. 2000; Fromang et al. 2002; Ilgner & Nelson 2006).”
Turbulent Mixing and the Dead Zone in Protostellar Disks (2006, background): “…surface density, the abundance of the dust that hastens recombination (Wardle & Ng 1999; Sano et al. 2000), the presence of long-lived metal ions (Fromang et al. 2002), and the rate at which the turbulence mixes the charged species into the interior ( Inutsuka & Sano 2005; Ilgner & Nelson 2006b).”