Signatures of broken protoplanetary discs in scattered light and in sub-millimetre observations

TL;DR

This study uses 3D simulations and radiative transfer modeling to identify observational signatures of warped or broken protoplanetary discs caused by stellar companions, highlighting azimuthal asymmetries and kinematic features.

Contribution

It demonstrates how precessing inner discs produce observable asymmetries and signatures in scattered light and sub-millimetre lines, applicable to various disc configurations.

Findings

Azimuthal asymmetries in scattered light depend on misalignment angle.

Asymmetric surface brightness maps of CO lines reveal disc structure.

Kinematic data can distinguish between radial inflow and misaligned inner discs.

Abstract

Spatially resolved observations of protoplanetary discs are revealing that their inner regions can be warped or broken from the outer disc. A few mechanisms are known to lead to such 3D structures; among them, the interaction with a stellar companion. We perform a 3D SPH simulation of a circumbinary disc misaligned by $60^\circ$ with respect to the binary orbital plane. The inner disc breaks from the outer regions, precessing as a rigid body, and leading to a complex evolution. As the inner disc precesses, the misalignment angle between the inner and outer discs varies by more than $100^\circ$. Different snapshots of the evolution are post-processed with a radiative transfer code, in order to produce observational diagnostics of the process. Even though the simulation was produced for the specific case of a circumbinary disc, most of the observational predictions hold for any disc hosting a precessing inner rim. Synthetic scattered light observations show strong azimuthal asymmetries, where the pattern depends strongly on the misalignment angle between inner and outer disc. The asymmetric illumination of the outer disc leads to azimuthal variations of the temperature structure, in particular in the upper layers, where the cooling time is short. These variations are reflected in asymmetric surface brightness maps of optically thick lines, as CO $J$=3-2. The kinematical information obtained from the gas lines is unique in determining the disc structure. The combination of scattered light images and (sub-)mm lines can distinguish between radial inflow and misaligned inner disc scenarios.