Rossby wave instability in weakly ionized protoplanetary disks. I. azimuthal or vertical B-fields

TL;DR

This paper investigates how magnetic fields and non-ideal MHD effects influence Rossby wave instability in weakly ionized protoplanetary disks, revealing that magnetism can both enhance and suppress RWI growth depending on conditions.

Contribution

It provides the first linear analysis of RWI in magnetized, weakly ionized disks including non-ideal MHD effects, extending previous hydrodynamic studies.

Findings

Magnetic fields can either enhance or suppress RWI growth.

Non-ideal MHD effects tend to recover hydrodynamic RWI growth rates.

Vertical wavenumbers generally reduce RWI growth rates.

Abstract

Rossby wave instability (RWI) is considered the underlying mechanism to crescent-shaped azimuthal asymmetries, discovered in (sub-)millimeter dust continuum of many protoplanetary disks. Previous works on linear theory were conducted in the hydrodynamic limit. Nevertheless, protoplanetary disks are likely magnetized and weakly ionized. We examine the influence of magnetic fields and non-ideal magnetohydrodynamic (MHD) effects - namely, Ohmic resistivity, Hall drift, and ambipolar diffusion - on the RWI unstable modes. We perform radially global linear analyses, employing constant azimuthal ($B_\phi$) or vertical ($B_z$) background magnetic fields. It is found that, in the ideal MHD regime, magnetism can either enhance or diminish RWI growth. Strong non-ideal MHD effects cause RWI growth rates to recover hydrodynamic results. The sign of Hall Els\"{a}sser number subtly complicates the results, and vertical wavenumbers generically diminish growth rates.