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 Title: Inside-out planet formation. V. structure of the inner disk as implied by the MRI Authors: Mohanty, SJankovic, MRTan, JCOwen, JE Item Type: Journal Article Abstract: The large population of Earth to super-Earth sized planets found very close to their host stars has motivated consideration of $in$ $situ$ formation models. In particular, Inside-Out Planet Formation is a scenario in which planets coalesce sequentially in the disk, at the local gas pressure maximum near the inner boundary of the dead zone. The pressure maximum arises from a decline in viscosity, going from the active innermost disk (where thermal ionization of alkalis yields high viscosities via the magneto-rotational instability (MRI)) to the adjacent dead zone (where the MRI is quenched). Previous studies of the pressure maximum, based on $\alpha$-disk models, have assumed ad hoc values for the viscosity parameter $\alpha$ in the active zone, ignoring the detailed physics of the MRI. Here we explicitly couple the MRI criteria to the $\alpha$-disk equations, to find steady-state (constant accretion rate) solutions for the disk structure. We consider the effects of both Ohmic and ambipolar resistivities, and find solutions for a range of disk accretion rates ($\dot{M}$ = $10^{-10}$ - $10^{-8}$ ${\rm M}_{\odot}$/yr), stellar masses ($M_{\ast}$ = 0.1 - 1 ${\rm M}_{\odot}$), and fiducial values of the $non$-MRI $\alpha$-viscosity in the dead zone ($\alpha_{\rm {DZ}} = 10^{-5}$ - $10^{-3}$). We find that: (1) A midplane pressure maximum forms radially $outside$ the inner boundary of the dead zone; (2) Hall resistivity dominates near the midplane in the inner disk, which may explain why close-in planets do $not$ form in $\sim$50% of systems; (3) X-ray ionization can be competitive with thermal ionization in the inner disk, because of the low surface density there in steady-state; and (4) our inner disk solutions are viscously unstable to surface density perturbations. Issue Date: 13-Jul-2018 Date of Acceptance: 5-Apr-2018 URI: http://hdl.handle.net/10044/1/55670 DOI: 10.3847/1538-4357/aabcd0 ISSN: 0004-637X Publisher: American Astronomical Society Start Page: 1 End Page: 27 Journal / Book Title: Astrophysical Journal Volume: 861 Issue: 2 Replaces: 10044/1/60199http://hdl.handle.net/10044/1/60199 Copyright Statement: © 2017 The Authors Sponsor/Funder: The Royal SocietyScience and Technology Facilities CouncilScience and Technology Facilities Council (STFC) Funder's Grant Number: UF150412ST-N000838ST/N000838/1 Keywords: Science & TechnologyPhysical SciencesAstronomy & Astrophysicsplanets and satellites: formationprotoplanetary disksMAGNETOROTATIONAL INSTABILITYACCRETION DISKSNONLINEAR EVOLUTIONPROTOSTELLAR DISKSSATURATION LEVELGIANT PLANETTURBULENCEDUSTIONIZATIONMIGRATIONastro-ph.SRastro-ph.SRastro-ph.SRastro-ph.SR0201 Astronomical and Space Sciences0202 Atomic, Molecular, Nuclear, Particle and Plasma Physics0306 Physical Chemistry (incl. Structural)Astronomy & Astrophysics Notes: 34 pages, 28 figures, 3 appendices. Accepted by the Astrophysical Journal Publication Status: Published Open Access location: https://arxiv.org/abs/1712.07049 Online Publication Date: 2018-07-13 Appears in Collections: PhysicsAstrophysicsFaculty of Natural Sciences