Local semi-analytic models of magnetic flux transport in protoplanetary discs

Leung, Philip K. C.; Ogilvie, Gordon I.

doi:10.1093/mnras/stz1620

Cited by 15 publications

(7 citation statements)

References 51 publications

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“…Thus, we now turn to studying the evolution of the flux itself. We remark that including the Hall effect (albeit with a simplified ionization prescription) has been found to have a significant effect on the radial transport of the vertical magnetic field (Bai & Stone 2017;Leung & Ogilvie 2019). This redistribution of flux was attributed to a global manifestation of the HSI, and a similar result has been found in Hall-MHD simulations of cloud collapse by Tsukamoto et al (2017).…”

Section: Evolution Of the Magnetic Fluxsupporting

confidence: 73%

Global Hydromagnetic Simulations of Protoplanetary Disks with Stellar Irradiation and Simplified Thermochemistry

Gressel,

Ramsey,

Brinch

et al. 2020

Preprint

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Outflows driven by large-scale magnetic fields likely play an important role in the evolution and dispersal of protoplanetary disks, and in setting the conditions for planet formation. We extend our 2-D axisymmetric non-ideal MHD model of these outflows by incorporating radiative transfer and simplified thermochemistry, with the twin aims of exploring how heating influences wind launching, and illustrating how such models can be tested through observations of diagnostic spectral lines. Our model disks launch magnetocentrifugal outflows primarily through magnetic tension forces, so the mass-loss rate increases only moderately when thermochemical effects are switched on. For typical field strengths, thermochemical and irradiation heating are more important than magnetic dissipation. We furthermore find that the entrained vertical magnetic flux diffuses out of the disk on secular timescales as a result of non-ideal MHD. Through post-processing line radiative transfer, we demonstrate that spectral line intensities and moment-1 maps of atomic oxygen, the HCN molecule, and other species show potentially observable differences between a model with a magnetically driven outflow and one with a weaker, photoevaporative outflow. In particular, the line shapes and velocity asymmetries in the moment-1 maps could enable the identification of outflows emanating from the disk surface.

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Section: Evolution Of the Magnetic Fluxsupporting

confidence: 73%

Global Hydromagnetic Simulations of Protoplanetary Disks with Stellar Irradiation and Simplified Thermochemistry

Gressel,

Ramsey,

Brinch

et al. 2020

Preprint

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“…Moreover, I find that the transport rate varies significantly with the strength of Ohmic diffusion and to a lesser extent with ambipolar diffusion. Overall, this dependence might explain why simulations and models tend to disagree on the magnetic transport rate (Bai & Stone 2017;Leung & Ogilvie 2019;Gressel et al 2020).…”

Section: Discussionmentioning

confidence: 99%

Systematic description of wind-driven protoplanetary discs

Lesur

2021

A&A

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Aims. Planet-forming discs are believed to be very weakly turbulent in the regions outside of 1 AU. For this reason, it is now believed that magnetised winds could be the dominant mechanism driving accretion in these systems. However, currently, no self-consistent approach can describe discs that are subject to a magnetised wind in a way similar to the α disc model. In this article, I explore the parameter space of wind-driven protoplanetary discs in a systematic manner and present scaling laws that can be used in reduced models in a similar way to α disc models. Methods. I computed a series of self-similar wind solutions, assuming that the disc is dominated by ambipolar and Ohmic diffusion. These solution were obtained by searching for stationary solutions in the finite-volume code PLUTO using a relaxation method and continuation. Results. Self-similar solutions are obtained for values of plasma β ranging from 102 to 108 for several Ohmic and ambipolar diffusion strengths. Mass accretion rates of about 10−8 M⊙ yr−1 are obtained for the poloidal field strength β = O(104) or equivalently, 1 mG at 10 AU. In addition, the ejection efficiency is always close to 1, implying that wind mass-loss rate can be higher than the inner mass accretion rate when the wind-emitting region is large. The resulting magnetic lever arms are typically lower than 2, possibly reaching 1.5 in the weakest field cases. Remarkably, the mean transport properties (accretion rate and mass-loss rate) mostly depend on the field strength and much less on the disc diffusivities or surface density. The disc internal structure is nevertheless strongly affected by Ohmic resistivity, strongly resistive discs being subject to accretion at the surface while ambipolar only models lead to mid-plane accretion. Finally, I provide a complete set of scaling laws and semi-analytical wind solutions, which can be used to fit and interpret observations. Conclusions. Magnetised winds are unavoidable in protoplanetary discs as soon as they are embedded in an ambient poloidal magnetic field. Very detailed disc microphysics are not always needed to describe them, and simplified models such as self-similar solutions can capture most of the physics seen in full 3D simulations. The remaining difficulty to set up a complete theory of wind-driven accretion lies in the transport of the large-scale field, which remains poorly constrained and is not well understood.

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“…This situation is very different from conventional theoretical models of flux transport, where the disk is typically assumed to be infinitely extended radially to permit radially-self-similar-type solutions. Under such assumptions, recent works start to incorporate more detailed disk vertical structure, as well as the role of disk winds (Leung & Ogilvie 2019;Lesur 2021). We anticipate that such approaches may still be applicable well within the truncation radius r c , but new theories are needed for regions beyond disk truncation to determine the global rate of flux transport.…”

Section: Global Transport Of Magnetic Fluxesmentioning

confidence: 99%

“…Early works of magnetic flux transport generally belong to the advection-diffusion framework (Lubow et al 1994), where inward advection of magnetic flux due to viscously-driven accretion competes with outward diffusion from disk (turbulent) resistivity, with later semianalytical studies that incorporate disk vertical structure (Rothstein & Lovelace 2008;Guilet & Ogilvie 2012, and radial resistivity profile (Okuzumi et al 2014;, though these works largely ignored the wind-driven accretion process and additional non-ideal MHD effects (other than resistivity). More recently, magnetic flux transport is studied from more realistic global disk simulations (Bai & Stone 2017), semianalytical local calculations (Leung & Ogilvie 2019), and self-similar numerical solutions (Lesur 2021), which generally find outward flux transport whose rates increases with disk magnetization, in addition to other dependencies. It remains to study, however, how the results are affected by the presence of disk outer truncation, which will likely yield different field geometries with important consequences to global flux transport.…”

Section: Introductionmentioning

confidence: 99%

Global Non-ideal Magnetohydrodynamic Simulations of Protoplanetary Disks with Outer Truncation

Yang,

Bai

2021

Preprint

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It has recently been established that the evolution of protoplanetary disks is primarily driven by magnetized disk winds, requiring large-scale magnetic flux threading the disks. The size of such disks is expected to shrink in time, as opposed to the conventional scenario of viscous expansion. We present the first global 2D non-ideal magnetohydrodynamic (MHD) simulations of protoplanetary disks that are truncated in the outer radius, aiming to understand the interaction of the disk with the interstellar environment, as well as global evolution of the disk and magnetic flux. We find that as the system relaxes, poloidal magnetic field threading the disk beyond the truncation radius collapses towards the midplane, leading to rapid reconnection. This process removes a substantial amount of magnetic flux from the system, and forms closed poloidal magnetic flux loops encircling the outer disk in quasisteady-state. These magnetic flux loops can drive expansion beyond truncation radius, corresponding to substantial mass loss through magnetized disk outflow beyond truncation radius analogous to a combination of viscous spreading and external photoevaporation. The magnetic flux loops gradually shrink over time whose rates depend on level of disk magnetization and external environments, which eventually governs the long-term disk evolution.

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Local semi-analytic models of magnetic flux transport in protoplanetary discs

Cited by 15 publications

References 51 publications

Global Hydromagnetic Simulations of Protoplanetary Disks with Stellar Irradiation and Simplified Thermochemistry

Global Hydromagnetic Simulations of Protoplanetary Disks with Stellar Irradiation and Simplified Thermochemistry

Systematic description of wind-driven protoplanetary discs

Global Non-ideal Magnetohydrodynamic Simulations of Protoplanetary Disks with Outer Truncation

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