GLOBAL SIMULATIONS OF PROTOPLANETARY DISKS WITH OHMIC RESISTIVITY AND AMBIPOLAR DIFFUSION

By Oliver Gressel, N. J. Turner, R. Nelson, C. McNally. 2015

175 citations recorded by the source corpus.

Protoplanetary disks (PPDs) are believed to accrete onto their central T Tauri star because of magnetic stresses. Recently published shearing box simulations indicate that Ohmic resistivity, ambipolar diffusion (AD) and the Hall effect all play important roles in disk evolution. In the presence of a vertical magnetic field, the disk remains laminar between 1– 5 AU ?> , and a magnetocentrifugal disk wind forms that provides an important mechanism for removing angular momentum. Questions remain, however, about the establishment of a true physical wind solution in the shearing box simulations because of the symmetries inherent in the local approximation. We present global MHD simulations of PPDs that include Ohmic resistivity and AD, where the time-dependent gas-phase electron and ion fractions are computed under FUV and X-ray ionization with a simplified recombination chemistry. Our results show that the disk remains laminar, and that a physical wind solution arises naturally in global disk models. The wind is sufficiently efficient to explain the observed accretion rates. Furthermore, the ionization fraction at intermediate disk heights is large enough for magneto-rotational channel modes to grow and subsequently develop into belts of horizontal field. Depending on the ionization fraction, these can remain quasi-global, or break-up into discrete islands of coherent field polarity. The disk models we present here show a dramatic departure from our earlier models including Ohmic resistivity only. It will be important to examine how the Hall effect modifies the evolution, and to explore the influence this has on the observational appearance of such systems, and on planet formation and migration.

Subfields: Astronomy and Astrophysics

View Paper: https://www.semanticscholar.org/paper/e437d347e630a2f20eeb21245de29019bf2512b2

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In Astronomy and Astrophysics

Citations in the corpus

Accretion onto Pre-Main-Sequence Stars (2016, methodology): “Panel b adapted from Gressel et al. (2015) with permission.”
Global Simulations of the Inner Regions of Protoplanetary Disks with Comprehensive Disk Microphysics (2017, background): “This layer is likely unstable to the Kelvin– Helmholtz instability, as found in surface current layers in some of the Hall-free simulations from Gressel et al. (2015).”
Global simulations of protoplanetary disks with net magnetic flux: I. Non-ideal MHD case (2016, methodology): “We presume that Gressel et al. (2015) did not observe this phenomenon because of the lower magnetization and ionization fraction in their simulations.”
Formation of planetary systems by pebble accretion and migration (2018, methodology): “This supports the use of low values of α for the midplane turbulence, without increasing the surface density of the disc Σ as 1/α (Suzuki & Inutsuka 2009; Bai 2014, 2017; Lesur et al. 2014; Gressel et al. 2015).”
ALMA Survey of Lupus Protoplanetary Disks. II. Gas Disk Radii (2018, background): “Such disk winds, magnetically launched from several au radii, have been theorized in non-ideal MHD models (Gressel et al. 2015), including even one-sided flows (Bai 2017), and have been observed in recent ALMA observations (Bjerkeli et al. 2016; Hirota et al. 2017).”
ALMA SURVEY OF LUPUS PROTOPLANETARY DISKS. I. DUST AND GAS MASSES (2016, background): “This may be the root cause of the preferential loss of gas relative to dust via photoevaporation (Alexander et al. 2014), layered accretion (Gammie 1996), and/or disk winds (Gressel et al. 2015; Bai et al. 2016).”