MRI-active inner regions of protoplanetary discs – II. Dependence on dust, disc, and stellar parameters
File(s)
Accepted version
Author(s)
Jankovic, Marija R
Mohanty, Subhanjoy
Owen, James E
Tan, Jonathan C
Type
Journal Article
Abstract
Close-in super-Earths are the most abundant exoplanets known. It has been hypothesized that they form in the inner regions of protoplanetary discs, out of the dust that may accumulate at the boundary between the inner region susceptible to the magneto-rotational instability (MRI) and an MRI-dead zone further out. In Paper I, we presented a model for the viscous inner disc which includes heating due to both irradiation and MRI-driven accretion; thermal and non-thermal ionization; dust opacities; and dust effects on ionization. Here, we examine how the inner disc structure varies with stellar, disc, and dust parameters. For high accretion rates and small dust grains, we find that: (1) the main sources of ionization are thermal ionization and thermionic and ion emission; (2) the disc features a hot, high-viscosity inner region, and a local gas pressure maximum at the outer edge of this region (in line with previous studies); and (3) an increase in the dust-to-gas ratio pushes the pressure maximum outwards. Consequently, dust can accumulate in such inner discs without suppressing the MRI, with the amount of accumulation depending on the viscosity in the MRI-dead regions. Conversely, for low accretion rates and large dust grains, there appears to be an additional steady-state solution in which: (1) stellar X-rays become the main source of ionization; (2) MRI-viscosity is high throughout the disc; and (3) the pressure maximum ceases to exist. Hence, if planets form in the inner disc, larger accretion rates (and thus younger discs) are favoured.
Date Issued
2021-12-15
Date Acceptance
2021-11-15
Citation
Monthly Notices of the Royal Astronomical Society, 2021, 509 (4), pp.5974-5991
ISSN
0035-8711
Publisher
Oxford University Press (OUP)
Start Page
5974
End Page
5991
Journal / Book Title
Monthly Notices of the Royal Astronomical Society
Volume
509
Issue
4
Copyright Statement
© 2021 The Author(s) Published by Oxford University Press on behalf of Royal Astronomical Society
This article is published and distributed under the terms of the Oxford University Press, Standard Journals Publication Model (https://academic.oup.com/journals/pages/open_access/funder_policies/chorus/standard_publication_model)
This article is published and distributed under the terms of the Oxford University Press, Standard Journals Publication Model (https://academic.oup.com/journals/pages/open_access/funder_policies/chorus/standard_publication_model)
Sponsor
The Royal Society
Commission of the European Communities
The Royal Society
Identifier
https://academic.oup.com/mnras/article/509/4/5974/6438446
Grant Number
UF150412
853022
RGF\EA\201038
Subjects
0201 Astronomical and Space Sciences
Astronomy & Astrophysics
Publication Status
Published
Date Publish Online
2021-11-24