GW Ori: circumtriple rings and planets

TL;DR

This study investigates the origin of dust rings in the GW Ori triple star system, suggesting that undetected planets likely cause the disc breaking and ring misalignments, rather than the stellar torque.

Contribution

It provides the first evidence that planets, not stellar torque, are responsible for disc breaking in a circumtriple system, based on simulations and observations.

Findings

Disc does not break due to stellar torque in GW Ori.

Presence of massive planets likely causes disc breaking.

Disc rings are misaligned and precess due to planetary influence.

Abstract

GW Ori is a hierarchical triple star system with a misaligned circumtriple protoplanetary disc. Recent ALMA observations have identified three dust rings with a prominent gap at $100\, \rm au$ and misalignments between each of the rings. A break in the gas disc may be driven either by the torque from the triple star system or a planet that is massive enough to carve a gap in the disc. Once the disc is broken, the rings nodally precess on different timescales and become misaligned. We investigate the origins of the dust rings by means of $N$-body integrations and 3-dimensional hydrodynamic simulations. We find that for observationally-motivated parameters of protoplanetary discs, the disc does not break due to the torque from the star system. We suggest that the presence of a massive planet (or planets) in the disc separates the inner and outer disc. We conclude that the disc breaking in GW Ori is likely caused by undetected planets -- the first planet(s) in a circumtriple orbit.