We perform magnetohydrodynamic simulations of protoplanetary disc gaps opened by planets
of various masses, with the aim of calculating the strength of the vertical magnetic field
threading such gaps. We introduce a gravitational potential at the centre of a shearing box to
compute the tidal interaction between the planets and the disc gas, which is turbulent due to
the magnetorotational instability. Two types of simulations are executed: 1) In type ‘Z’, the
initial magnetic field has only a uniform, vertical component, and ten planet masses between
0.66 and 6.64 thermal masses are used; 2) In type ‘YZ’, the initial magnetic field has both
toroidal and vertical components, and five planet masses covering the same mass range are
used. Our results show that, for low planet masses, higher values of the vertical magnetic field
occur inside the gaps than outside, in agreement with the previous work. However, for massive
planets, we find that the radial profiles of the field show dips near the gap centre. The interior
of the Hill sphere of the most massive planet in the Z runs contains more low-plasma β values
(i.e. high magnetic pressure) compared to lower-mass planets. Values of β at a distance of one
Hill radius from each planet show a moderate decrease with planet mass. These results are
relevant for the magnetic structure of circumplanetary discs and their possible outflows, and
may be refined to aid future observational efforts to infer planet masses from high-resolution
polarimetric observations of discs with gaps.
protoplanetary disks
magnetohydrodynamics
disk gap