Thinkshop 2020

Many planets orbit within an AU of their stars, raising questions about their origins. Particularly puzzling are the planets found near the silicate sublimation front. We investigate conditions near the front in the protostellar disk around a young intermediate-mass star, using the first global 3-D radiation non-ideal MHD simulations in this context.

The results show magnetorotational turbulence around the sublimation front at 0.5 AU. Beyond 0.8 AU is the dead zone, cooler than 1000 K and with turbulence orders of magnitude weaker. A local pressure maximum just inside the dead zone concentrates solid particles, allowing for efficient growth. Over many orbits, a vortex develops at the dead zone's inner edge, increasing the disk's thickness locally by around 10%.

We synthetically observe the results using Monte Carlo transfer calculations, finding the sublimation front is bright in the near-infrared. The models with vertical magnetic flux develop extended, magnetically-supported atmospheres that reprocess extra starlight, raising the near-infrared flux 20%. The vortex throws a non-axisymmetric shadow on the outer disk.

Radiation-MHD models of the kind we demonstrate open a new window for investigating protoplanetary disks' central regions. They are ideally suited for exploring young planets' formation environment, interactions with the disk, and orbital migration, in order to understand the origins of the close-in exoplanets.